A double-layer porous ceramic plate and its preparation method and application

Abstract

The present invention discloses a double-layer porous ceramic plate and a preparation method and application thereof. The double-layer porous ceramic plate comprises an interception layer and a support layer, the interception layer has through holes, the interception layer has a thickness of 25-200 μm, the support layer has a cavity structure, the through holes of the interception layer are connected to the cavity structure of the support layer, and the through porosity of the double-layer porous ceramic plate is greater than 50%. When the double-layer porous ceramic plate of the present invention is used to filter sewage containing solid particles, it is not easy to be blocked, and the filtering performance can be restored by backwashing technology. It has the characteristics of high performance and low cost and is suitable for industrial applications.

Description

Technical Field

[0001] The present application relates to the field of ceramic filter materials, and in particular, to a double-layer porous ceramic plate and a preparation method and application thereof. Background Art

[0002] In the production process of industrial enterprises, especially in the chemical, metallurgical, steel and other industries, industrial wastewater containing solid particles such as suspended matter and colloidal particles is often generated. With the gradual improvement of environmental protection supervision requirements, production enterprises usually need to treat industrial wastewater to meet the discharge standards before they can be discharged. Filtering solid particles in industrial wastewater is an important part of wastewater treatment. In the metal processing process, emulsions are usually used for lubrication and cooling. Usually, emulsions are recycled, and the metal or non-metallic solid particles generated during the processing will be mixed into the emulsion. In order to ensure the cleanliness of the emulsion, the solid particles mixed into the emulsion need to be filtered.

[0003] The principle of filtration is to use the tiny holes on the filter material. When sewage containing solid particles passes through the filter material, the solid particles in the sewage with a particle size larger than the hole size of the filter material are retained on the surface of the filter medium, thereby achieving the effect of sewage purification. Ceramic filter materials have the characteristics of corrosion resistance, high temperature resistance, and high mechanical strength, and can be used to filter industrial sewage or separate solids and liquids.

[0004] Traditional ceramic plates are mainly prepared by a layer-by-layer stacking process using a powder-particle stacking pressing process. Generally, it is composed of a support layer, a transition layer, and a separation layer. The function of the support layer is to increase the mechanical strength of the membrane. The aperture of the through hole of the transition layer is smaller than that of the through hole of the support layer. The pore size distribution of the entire membrane gradually decreases from the support layer to the membrane layer, forming an asymmetric structural distribution. Due to the pressing process used in the above-mentioned production method, the through hole aperture of the traditional ceramic plate is small, which is easy to form irregular and unconnected channels, and the through porosity is usually 30-40%. Although the through hole aperture of the plate-type ceramic plate gradually increases from the separation layer to the support layer, the aperture of the through hole does not increase much, the overall aperture is very small, and the through porosity is low, which easily causes the membrane pores to be blocked, thereby affecting normal use. It has high requirements for the quality of the influent water and is not suitable for filtering solid particles in industrial wastewater.

[0005] The Chinese patent document with publication number CN117181010A discloses an inorganic double-layer ceramic plate and its preparation method and application. The method is to mix sludge powder, pore-forming agent and solvent evenly, crush them after drying, press them into ceramic sheets and then sinter them at high temperature to obtain a ceramic plate support. Then, the sludge powder, binder and organic solvent are mixed evenly to obtain a membrane solution, and the membrane solution is applied to the ceramic plate support, and the inorganic double-layer ceramic plate is obtained after high-temperature sintering. However, the support of this method is obtained by sintering after compression molding, and the internal pores of the support are small, generally less than 5μm. Therefore, the inorganic double-layer ceramic plate in the patent document cannot be applied to industrial sewage filtration. In addition, in this method, the membrane solution is applied to the sintered ceramic plate support, and then secondary sintering is performed, so that the connection between the separation layer of the ceramic plate and the support is less reliable.

[0006] At present, filter paper and filter cloth are usually used to filter emulsions containing solid particles. However, filter paper and filter cloth can only be used once, have a short service life and high cost. In addition, since filter paper and filter cloth are made by spray melting, the pore size will expand and enlarge as the pressure increases during use, resulting in reduced filtering effect. In addition, filter paper and filter cloth will also absorb a certain amount of oil, which will reduce the content of oil used for lubrication in the emulsion.

[0007] Since ceramic materials are reusable, the filtration cost can be significantly reduced. Therefore, there is an urgent need for a ceramic filter material suitable for filtering industrial wastewater containing solid particles. Summary of the invention

[0008] One purpose of the present application is to provide a double-layer porous ceramic plate and a preparation method thereof, so as to solve the problem that traditional ceramic membranes are not suitable for treating industrial wastewater containing solid particles and the existing technology has high treatment costs.

[0009] In order to achieve the above-mentioned purpose, the first aspect of the present invention provides a double-layer porous ceramic plate, which includes an intercepting layer and a supporting layer, the intercepting layer has through holes, wherein the intercepting layer has a thickness of 25-200μm, the supporting layer has a cavity structure, the through holes of the intercepting layer are connected to the cavity structure of the supporting layer, and the through porosity of the double-layer porous ceramic plate is greater than 50%.

[0010] Preferably, the intercepting layer has a thickness of 40-101 μm.

[0011] Furthermore, the through porosity of the double-layer porous ceramic plate is 52%-80%.

[0012] Furthermore, the proportion of through holes in the intercepting layer having a pore size larger than the preset filtering pore size to the number of through holes having a pore size larger than 5 μm is less than 20%.

[0013] In some embodiments, the thickness of the support layer is greater than 8 mm.

[0014] Furthermore, the thickness of the support layer is 8-32 mm.

[0015] Further, the cavity structure of the support layer is formed using a foaming process.

[0016] Furthermore, the double-layer porous ceramic plate is prepared by using quartz powder.

[0017] In a second aspect of the present invention, a method for preparing a double-layer porous ceramic plate is provided, comprising the following steps: S1, mixing a first ceramic powder, water, an adhesive and a foam stabilizer, to form a first mixed slurry; S2, adding a foaming agent to the first mixed slurry, mixing and stirring to form a foam slurry; S3, injecting the foam slurry into a mold having at least one surface covered with oil paper, and taking out a ceramic rough embryo after natural drying, wherein the contact surface between the ceramic rough embryo and the oil paper forms an interception layer; S4, using a second ceramic The dry powder of the ceramic powder fills the pores of the intercepting layer of the ceramic rough embryo to form a ceramic embryo; S5, the ceramic embryo is roasted, the temperature is increased to 900-1300°C at a heating rate of 4-10°C / min, and the temperature is kept for 1-5 hours to obtain a double-layer porous ceramic plate; wherein the raw materials of the foam slurry are as follows according to mass percentage: the first ceramic powder is 38-60%, water is 32-60%, the adhesive is 0.5-3%, the foam stabilizer is 0.5-3%, and the foaming agent is 1-2%.

[0018] In some preferred embodiments, the raw materials of the foam slurry are as follows in terms of mass percentage: 48-52% of first ceramic powder, 42-50% of water, 0.5-2% of adhesive, 0.5-2% of foam stabilizer, and 1-2% of foaming agent.

[0019] In some embodiments, the mesh size of the first ceramic powder is 150-550 mesh. In some embodiments, the first ceramic powder and the second ceramic powder are any one or more of quartz, diatomaceous earth, mullite, kaolin, sepiolite, and dolomite.

[0020] Preferably, the first ceramic powder and the second ceramic powder are both quartz.

[0021] In some embodiments, the adhesive is any one or more of sodium carboxymethyl cellulose, hydroxyethyl cellulose, xanthan gum, and gelatin.

[0022] In some embodiments, the foaming agent is any one or more of sodium dodecyl sulfate, lauroyl diethanolamine, sodium dodecylaminopropionate, triethanolamine lauryl sulfate, and carbonates.

[0023] In some embodiments, the foam stabilizer is any one or more of polyvinyl alcohol, modified starch, and silicone polyether emulsion.

[0024] The third aspect of the present invention provides a double-layer porous ceramic plate prepared by the above-mentioned preparation method.

[0025] The fourth aspect of the present invention also provides an application of the double-layer porous ceramic plate of the present invention in filtering sewage containing solid particles.

[0026] The method for preparing a double-layer porous ceramic plate of the present invention is based on the foamed ceramic process. Oil paper is used on the surface of a mold to make a blank, and dry powder is further used to fill the pores on the surface of the ceramic blank, thereby preparing a double-layer porous ceramic plate including an intercepting layer and a supporting layer.

[0027] The double-layer porous ceramic plate prepared by the method of the present invention has the following characteristics: it includes an intercepting layer and a supporting layer, the thickness of the intercepting layer is extremely thin, which is equivalent to the particle size of the ceramic powder particles, and the number of through holes in the intercepting layer whose pore size is larger than the preset filter pore size is extremely small; the supporting layer has a cavity structure including a large number of gaps.

[0028] When the double-layer porous ceramic plate of the present invention is used to filter sewage containing solid particles, clogging is not likely to occur. In addition, the double-layer porous ceramic plate can be backwashed after being used for a period of time by using backwashing technology to remove solid particles attached to the through holes of the interception layer and restore the filtration flux. Therefore, it can be used repeatedly, thereby reducing the cost of sewage filtration and improving the efficiency of sewage filtration.

[0029] In addition, by further selecting quartz ceramic powder as the basic material, the double-layer porous ceramic plate prepared has the characteristics of stable physical properties and not prone to expansion, making the present invention suitable for large-scale industrial application.

[0030] The above is an overview of the present application, which may be simplified, summarized, and have omitted details. Therefore, those skilled in the art should appreciate that this part is only illustrative and is not intended to limit the scope of the present application in any way. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The above and other features of the present application will be more fully understood through the following description and the attached claims in conjunction with the accompanying drawings. It is understood that these drawings only depict several embodiments of the present application and should not be considered as limiting the scope of the present application. By using the accompanying drawings, the present application will be more clearly and detailed.

[0032] Figure 1 A schematic diagram showing a plurality of first ceramic powder particles 10 forming pores through two-dimensional arrangement;

[0033] Figure 2A photograph taken when observing the surface of the intercepting layer of a ceramic rough blank prepared in step S3 using a magnifying glass is shown;

[0034] Figure 3 The application step S4 is shown, using the second ceramic powder 20 to Figure 1 Schematic diagram of the ceramic rough interception layer after pore filling;

[0035] Figure 4 A photograph taken when observing the surface of the intercepting layer of a ceramic blank prepared in step S4 using a magnifying glass is shown;

[0036] Figure 5 A SEM photograph of a cross section perpendicular to the intercepting layer of the double-layer porous ceramic plate prepared in Example C3 is shown;

[0037] Figure 6 The SEM photograph of the interception layer surface of the double-layer porous ceramic plate prepared in Example C3 is shown;

[0038] Figure 7 This is a particle size distribution diagram of solid particles in sewage before filtering the emulsion sewage containing solid particles produced by the grinding machine using the double-layer porous ceramic plate prepared in Example C3;

[0039] Figure 8 The filtration flux diagram of the double-layer porous ceramic plate prepared in Example C3 for filtering the emulsion wastewater containing solid particles produced by the grinding machine;

[0040] Fig. 9 The photos of the sewage before and after filtration when the double-layer porous ceramic plate prepared in Example C3 is used to filter the emulsified sewage containing solid particles produced by the grinding machine;

[0041] Fig.10 A comparison chart of pure water flux tests performed using double-layer porous ceramic plates prepared in Example B3 and Example C3 is shown. DETAILED DESCRIPTION

[0042] The technical solution of the present application is described in detail below in conjunction with the accompanying drawings. Without departing from the spirit or scope of the subject matter of the present application, other implementations may be adopted, and modifications, combinations, equivalent substitutions or other changes may be made, all of which clearly constitute part of the content of the present application and are included in the protection scope of the present application.

[0043] The preparation method of the double-layer porous ceramic plate of the present application includes steps S1-S5, wherein steps S1 and S2 are used to prepare foam slurry, and the raw materials of the foam slurry include a first ceramic powder, an adhesive, a foam stabilizer and a foaming agent, and the various raw materials and water are in the following mass percentages: 38-60% of the first ceramic powder, 32-60% of water, 0.5-3% of the adhesive, 0.5-3% of the foam stabilizer, and 1-2% of the foaming agent; preferably, the first ceramic powder is 48-52%, the water is 42-50%, the adhesive is 0.5-2%, the foam stabilizer is 0.5-2%, and the foaming agent is 1-2%. Steps S1-S5 are specifically as follows:

[0044] S1. Stir and mix the first ceramic powder, water, adhesive and foam stabilizer to form a first mixed slurry.

[0045] The first ceramic powder can be any one or more of quartz, diatomite, mullite, kaolin, sepiolite, and dolomite. In some embodiments, ceramic powders with a silicon dioxide content of more than 70% are preferred, such as diatomite powders with a silicon dioxide content of 82% and quartz powders with a silicon dioxide content of 95%. The mesh size of the first ceramic powder can be selected between 150 and 550 meshes.

[0046] The adhesive is any one or more of sodium carboxymethyl cellulose, hydroxyethyl cellulose, xanthan gum and gelatin, and is used to provide viscosity to the slurry.

[0047] The foam stabilizer can be any one or more of polyvinyl alcohol, modified starch, silicone resin polyether emulsion, and adding the foam stabilizer in advance can make the bubbles in the foam slurry of step S2 more durable and stable.

[0048] The stirring and mixing time may be 10 minutes or longer, and preferably 10 to 25 minutes.

[0049] S2. Add a foaming agent into the first mixed slurry and stir to form a foam slurry.

[0050] The foaming agent is any one or more of sodium dodecyl sulfate (K12), lauroyl diethanolamine, sodium dodecylaminopropionate, triethanolamine lauryl sulfate, and carbonates. After adding the foaming agent, air can be incorporated into the slurry during stirring to form a foam slurry.

[0051] The stirring and mixing time may be 5 minutes or longer, preferably 5 to 10 minutes.

[0052] S3. Inject the foam slurry into a mold covered with oil paper, and take out the ceramic rough embryo after natural drying.

[0053] The shape of the mold can be determined according to the shape of the ceramic rough blank required. The oil paper is a processed paper made by coating tung oil or other drying oil on a flexible surface. The oil paper is covered on the surface of the mold, for example, by pasting the oil paper on at least one surface of the bottom and / or side of the mold, and the surface coated with the drying oil faces outward.

[0054] In the prior art, release paper is usually used on the mold surface to separate the mold and the ceramic rough embryo. Although ordinary release paper can separate the ceramic rough embryo from the mold, it is easy to adhere to the ceramic powder particles.

[0055] In this step, by using oil paper on the surface of the mold, on the one hand, the ceramic slurry can be prevented from sticking to the surface of the mold, and after the slurry is dried, the ceramic rough blank can be easily removed from the mold. On the other hand, the inventors of the present application found that after the foamed slurry is injected into the mold with the surface covered with oil paper, the ceramic powder particles close to the oil paper are arranged in a two-dimensional manner to form an extremely thin surface layer with a thickness of about 1-2 times the particle size of the ceramic powder. For example, if the first ceramic powder is 150-550 mesh, an interception layer with a thickness of about 25-200μm can be formed. At the same time, since the ceramic powder has an irregular shape, there are pores between the ceramic powder particles close to the oil paper. In addition, due to the presence of bubbles in the foam slurry, the bubbles close to the oil paper cause a large number of pores to appear on the surface, and some pores are even visible to the naked eye. Figure 1 A schematic diagram of pores formed by two-dimensional arrangement of a plurality of first ceramic powder particles 10 is shown. For the sake of convenience, these pores can be divided into small-sized pores 11 and large-sized pores 12. There is no clear dividing line between the pore sizes of the small-sized pores 11 and the large-sized pores 12, and they can be divided according to the needs of filtration. For example, if it is desired to intercept solid particles with a pore size greater than 50 μm, the pores with a pore size less than 50 μm can be called small-sized pores, and the pores with a pore size greater than 50 μm can be called large-sized pores.

[0056] The small-sized pores 11 are suitable for intercepting solid particles larger than the pore diameters of these pores, so the present invention refers to the extremely thin surface layer formed by the ceramic powder near the oil paper as an interception layer, and the pores formed between the ceramic powder particles on the interception layer as through holes passing through the interception layer. The prior art uses ordinary release paper, which is easy to adhere to the ceramic powder particles, and cannot form a two-dimensional arrangement of ceramic powder particles on the contact surface of the ceramic slurry and the release paper.

[0057] The rest of the ceramic rough blank except the interception layer is called the support layer. Unlike the interception layer, the ceramic powder particles in the support layer are connected in a three-dimensional stacking manner. Due to the effect of the foaming agent, a large number of cavity structures are formed inside the support layer. The thickness of the support layer can be controlled by setting the depth of the mold.

[0058] The through holes of the intercepting layer are interconnected with the cavities of the supporting layer to form through holes that penetrate the intercepting layer and the supporting layer.

[0059] In order to fully dry the ceramic blank, in some embodiments, the natural drying time is more than 48 hours.

[0060] Figure 2 A photograph taken when observing the surface of the intercepting layer of a ceramic rough blank prepared in step S3 using a magnifying glass is shown. From the picture, multiple large-sized pores visible to the naked eye can be seen, and some of the large-sized pores are marked with dotted circles in the picture.

[0061] S4, using the second ceramic powder dry powder to fill the pores of the intercepting layer of the ceramic rough blank to form a ceramic blank.

[0062] The second ceramic powder can be selected from any one or more of quartz, diatomaceous earth, mullite, kaolin, sepiolite, and dolomite; the second ceramic powder can be the same as the first ceramic powder or different from the first ceramic powder.

[0063] Step S4 can make the pores of the ceramic rough interception layer whose pore size is larger than the particle size of the second ceramic powder further filled with the second ceramic powder, thereby reducing the proportion of large-diameter through-holes. Therefore, the particle size of the second ceramic powder can be selected according to the needs of filtration. For example, if it is desired that the interception layer can intercept solid particles with a particle size greater than 50 μm, a second ceramic powder with a particle size slightly smaller than 50 μm can be used, such as a second ceramic powder that can pass through a 300-mesh sieve but cannot pass through a 350-mesh sieve; if the particle size of the second ceramic powder is much smaller than 50 μm, the pores of the interception layer may be overfilled, seriously reducing its flux. Figure 3 The application step S4 is shown, using the second ceramic powder 20 to Figure 1 The schematic diagram of the ceramic rough intercepting layer after pore filling is shown, and the effect of the second ceramic powder filling the large-sized pores 12 is shown in the figure.

[0064] Step S4 can be implemented in the following manner. First, the dry powder of the second ceramic powder is coated on the intercepting layer of the ceramic rough blank, and then the surface of the intercepting layer is cleaned with a brush. The purpose of cleaning is to remove the second ceramic powder particles that fall outside the pores of the intercepting layer, while retaining the second ceramic powder particles that fall into the pores of the intercepting layer. Generally speaking, the more the second ceramic powder dry powder is coated, the more uniform the cleaning is, and the second ceramic powder particles can fully cover the through holes with pore sizes larger than their particle sizes, thereby reducing the proportion of large-sized through holes that do not meet the filtering requirements. Through proper coating, the proportion of through holes with pore sizes larger than the particle size of the second ceramic powder particles in the intercepting layer can be made lower than a preset value, such as lower than 20%, 10%, 5%, and so on. In the case of sufficient coating, the proportion can even be lower than 1%.

[0065] Figure 4 A photograph taken when observing the surface of the intercepting layer of a ceramic blank prepared in step S4 using a magnifying glass is shown. From the figure, it can be seen that after the pore filling step, most of the large-sized pores are filled with the second ceramic powder particles.

[0066] S5. calcining the ceramic blank, raising the temperature to 900-1300° C. at a heating rate of 4-10° C. / min, and keeping the temperature for 1-5 hours to obtain a double-layer porous ceramic plate.

[0067] Through this step, the ceramic powder particles are melted and bonded together to form a ceramic material with good mechanical strength.

[0068] The double-layer porous ceramic plate prepared by the above method has a double-layer structure including an intercepting layer and a supporting layer, and can be used for filtering industrial wastewater containing solid particles. The surface of the intercepting layer has through holes with small apertures, and the interior of the supporting layer has a cavity structure produced by a foaming process. The through holes of the surface layer are interconnected with the cavities of the inner layer to form through holes that penetrate the surface layer and the supporting layer. Since the thickness of the intercepting layer is very thin, the small-aperture through holes of the intercepting layer quickly transition to the large-aperture cavities of the supporting layer. In addition, since the ceramic powder of the surface layer and the ceramic powder of the supporting layer are sintered together by high-temperature melting, a firm structure is formed.

[0069] In the present disclosure, the foaming process refers to a process step of adding a foaming agent to a ceramic slurry during the preparation of a ceramic material to form a cavity structure in the ceramic material.

[0070] It should be noted that in the present disclosure, the mesh number of ceramic powder refers to the mesh size of the sieve that the ceramic powder can pass through. In the present disclosure, the corresponding relationship between the mesh number of the sieve and the sieve aperture is shown in the following table:

[0071] Mesh Pore ​​size (μm) Mesh Pore ​​size (μm) 150 106 300 48 160 96 325 47 170 90 350 45 180 80 400 38 200 75 450 31 230 62 500 25 240 61 550 24 250 58 600 23 270 53

[0072] Figure 5 and Figure 6 The SEM photograph of the cross section perpendicular to the interception layer and the SEM photograph of the surface of the interception layer of the double-layer porous ceramic plate prepared in Example C3 of the third group of examples of the present disclosure below are respectively shown.

[0073] Figure 5 The interception layer 1 and the support layer 2 are shown as examples. The interception layer 1 has a very thin thickness h, and a large number of cavity structures can be seen in the support layer 2. Figure 6 As shown, the surface of the intercepting layer has many small-sized pores.

[0074] When the double-layer porous ceramic plate is used for sewage treatment containing solid particles, the sewage flows through the interception layer, and the solid particles in the sewage whose particle size exceeds the aperture of the through hole of the interception layer are intercepted, and the solid particles whose particle size is smaller than the aperture of the through hole of the interception layer can enter the support layer through the interception layer. At this time, due to the extremely thin thickness of the interception layer, the aperture suddenly becomes larger after the through hole of the interception layer transitions to the support layer, so that the small-sized solid particles that are not intercepted can pass through the support layer smoothly, and are not prone to clogging. The intercepted solid particles can be treated by precipitation and other methods.

[0075] As the filtration time increases, some through holes in the interception layer may be blocked by large-sized solid particles, resulting in a decrease in the sewage filtration flux. At this time, the structural characteristics of the double-layer porous ceramic plate disclosed in the present invention, that the support layer has a large-sized cavity, while the aperture of the through holes of the interception layer is very small, can be utilized, and the solid particles attached to the through holes of the interception layer can be washed away using backwashing technology, thereby restoring the filtration capacity of the double-layer porous ceramic plate. The specific process of backwashing is as follows: Use a liquid pump or an air pump to apply hydraulic pressure or air pressure from the support layer to the interception layer, so that the solid particles attached to the through holes of the interception layer fall off due to the pressure difference.

[0076] The double-layer porous ceramic plate, preparation method and application effect of the present application are further described below in conjunction with the embodiments.

[0077] In the present disclosure, the pore size distribution of the through holes of the interception layer is statistically analyzed by cross-sectional direct observation, that is, by taking SEM photos of the interception layer of the double-layer porous ceramic plate, the number of through holes of different sizes with a pore size greater than 5 μm per unit area is counted. Since the through holes are irregular in shape, the pore size of the through holes is defined as the average of the diameter of the inscribed circle and the diameter of the circumscribed circle of the through holes.

[0078] In order to clearly illustrate the structure of the double-layer porous ceramic plate disclosed in the present invention, it is necessary to further measure the thickness of the interception layer. The thickness of the interception layer can be intuitively understood as the closest distance from the outer surface of the interception layer to the cavity of the support layer. However, due to the randomness of the foaming process, the shape of the bubble structure of the support layer is irregular. Therefore, the distance from different areas of the outer surface of the interception layer to the nearest support layer cavity may be different. Therefore, in the present invention, the thickness of the interception layer of the structure of the double-layer porous ceramic plate can be expressed by an interval. The thickness of the interception layer can be obtained by measuring the SEM photograph of the cross-section of the double-layer porous ceramic plate perpendicular to the interception layer. The specific measurement process is: select a number of measurement points on the outer surface of the interception layer, and for each selected measurement point, along the direction perpendicular to the outer surface of the interception layer toward the support layer, the distance to the aperture of the through hole of the interception layer reaches the preset filter aperture, which is the thickness of the interception layer in the area where the measurement point is located. A certain statistic of the interception layer thickness measured at multiple measurement points can be used as a measure of the interception layer thickness of the double-layer porous ceramic plate. For example, the statistic can be the average value, or median value, of the interception layer thickness measured at multiple measurement points, or the average value or median value after removing the maximum and minimum values. Those skilled in the art will appreciate that the locations of the selected measurement points should be as dispersed as possible, and the number of measurement points should be as large as possible, in order to obtain a more reliable interception layer thickness range. In the present disclosure, the average value after removing the maximum and minimum values ​​is used as a measure of the interception layer thickness of the double-layer porous ceramic plate. In the present disclosure, the preset filter aperture can be set as needed. For example, if it is desired that the interception layer can intercept solid particles with a particle size greater than 50 μm, the preset filter aperture is 50 μm.

[0079] In the present disclosure, the through-porosity refers to the ratio of the sum of the volumes of the through-pores that are interconnected between the inside and outside of a ceramic material to the volume of the ceramic material, which can be measured in the following ways: (1) immersing the ceramic material to be tested in a liquid and measuring the increase in the liquid volume ΔV; (2) calculating its volume Vo based on the external dimensions of the ceramic material to be tested. Then the through-porosity η of the ceramic material to be tested is (Vo-ΔV) / Vo. Those skilled in the art will understand that, in the case where the pore size distribution of the through-pores of the intercepting layer is the same, generally speaking, the higher the through-porosity, the larger the volume occupied by the cavities of the supporting layer, and the less likely it is to be clogged. The double-layer porous ceramic plate disclosed in the present disclosure is prepared by a foaming process, and its through-porosity is generally greater than 50%, which is specifically related to parameters such as the amount of the foaming agent used and the stirring time. Different through-porosities can be obtained by changing the relevant parameters. The method disclosed in the present disclosure can prepare a double-layer porous ceramic plate with a through-porosity of 50%-80%.

[0080] In order to make the double-layer porous ceramic plate have a certain mechanical strength, the thickness of the support layer is set to be greater than 8 mm. Preferably, the thickness of the support layer is set to be in the range of 8-32 mm.

[0081] The present disclosure is further described below by examples. For ease of understanding, the examples of preparing double-layer porous ceramic plates using the method disclosed in the present disclosure are divided into three groups. Each example uses steps S1-S4, except that the parameters of the materials are different. The specific steps of each example are as follows: S1, stir and mix the above-mentioned diatomaceous earth powder, water, yellow collagen and polyvinyl alcohol, stir at a rate of 3000 rpm, stir for 20 minutes, and form a first mixed slurry; S2, add the above-mentioned K12 to the first mixed slurry and stir and mix, stir at a rate of 3000 rpm, stir for 8 minutes, and form a foam slurry; S3, inject the foam slurry into a rectangular mold with oil paper on the bottom, and take out the ceramic rough embryo after natural drying for 48 hours; S4, fill the pores of the ceramic rough embryo with the second ceramic powder dry powder to form a ceramic embryo; S5, roast the ceramic embryo, heat it to 1100°C at a heating rate of 4-10°C / min, and keep it warm for 4 hours to obtain a double-layer porous ceramic plate.

[0082] In the embodiment of the present disclosure, the preset interception aperture is 50 μm, so the second ceramic powder uses quartz powder with a particle size slightly smaller than 50 μm. Those skilled in the art can select the second ceramic powder with a suitable particle size according to the different preset interception apertures.

[0083] The first group of embodiments includes embodiments A1-A7. In this group, the main difference between the embodiments is the mass percentage of diatomaceous earth powder and the mass percentage of water. The corresponding process parameters and the parameters of the obtained double-layer porous ceramic plate are shown in Table 1.

[0084] In Example A1, the raw materials and water of the foam slurry are as follows in terms of mass percentage: 35% of the first ceramic powder, 60.5% of water, 0.5% of xanthan gum, 2% of polyvinyl alcohol, and 2% of K12. The mesh number of the first ceramic powder is 450 meshes. The first ceramic powder is diatomaceous earth with a silicon dioxide content of 82%.

[0085] The difference between Examples A2-A4 and Example A1 is that the mass percentages of the first ceramic powder and water are different, and other process parameters are the same. The specific parameters are shown in Table 1.

[0086] Table 1: First Group of Examples

[0087]

[0088] In this group of embodiments and subsequent embodiments, the proportion of through holes with pore sizes greater than 50 μm in the interception layer refers to the proportion of through holes with pore sizes greater than 50 μm in the interception layer to the number of through holes with pore sizes greater than 5 μm. Mechanical strength refers to the minimum pressure value that causes a double-layer porous ceramic plate with a thickness of 32 mm to rupture when a pressure perpendicular to the surface of the interception layer is applied to the double-layer porous ceramic plate. The thickness of the interception layer is obtained by taking an SEM photograph of a cross-section of the double-layer porous ceramic plate perpendicular to the interception layer, selecting 10 measurement points with an interval of 1 mm along the direction of the interception layer, measuring the thickness of the interception layer at the measurement point, and removing the maximum and minimum values ​​to obtain the average value of the thickness of the interception layer at the remaining 8 measurement points.

[0089] The results of the first group of examples show that the through porosity increases as the mass percentage of the first ceramic powder decreases. However, when the mass percentage of the first ceramic powder is lower than 38%, the through porosity does not increase much, but the mechanical strength of the ceramic plate decreases significantly. When the mass percentage of the first ceramic powder is higher than 60%, the through porosity decreases significantly. When the mesh size of the first ceramic powder is the same, the thickness of the interception layer is basically the same.

[0090] The second group of embodiments includes embodiments B1-B4. Based on embodiment A4, the mesh size of the first ceramic powder is changed, and the other parameters are the same as those of embodiment A4. Among them, the raw materials and water of the foam slurry of embodiment A4 are as follows in terms of mass percentage: the first ceramic powder is 52% (silicon dioxide content is 82%), water is 43.5%, xanthocollagen is 0.5%, polyvinyl alcohol is 2%, K12 is 2%, and the mesh size of the first ceramic powder is 450 meshes. The corresponding process parameters of the second group of embodiments and the parameters of the obtained double-layer porous ceramic plate are shown in Table 2. For the convenience of comparison, the results of embodiment A4 in Table 1 are added to Table 2.

[0091] Table 2 Second Group of Examples

[0092]

[0093] By comparing the parameters and technical effects of the second group of embodiments, it can be seen that the thickness of the interception layer is related to the mesh number of the first ceramic powder or the particle size of the ceramic powder. The smaller the particle size of the ceramic powder, the smaller the thickness of the interception layer. The through-porosity has a certain correlation with the mesh number of the first ceramic powder. As the mesh number of the first ceramic powder increases, that is, the particle size of the ceramic powder decreases, the through-porosity increases. However, after the mesh number of the first ceramic powder exceeds 450 meshes, the through-porosity no longer increases.

[0094] The third group of embodiments includes embodiments C1-C3. The first ceramic powder of this group of embodiments is quartz with a silicon dioxide content of 95%. The main difference between the embodiments is the different mesh sizes of the first ceramic powder. The raw materials and water of the foam slurry of embodiments C1-C3 are as follows: 52% of the first ceramic powder, 43.5% of water, 0.5% of xanthocollagen, 2% of polyvinyl alcohol, and 2% of K12 in terms of mass percentage. The corresponding process parameters of the third group of embodiments and the parameters of the obtained double-layer porous ceramic plate are shown in Table 3.

[0095] Table 3 The third group of examples

[0096]

[0097] By comparing the parameters and technical effects of the third group of examples, it can be seen that the first ceramic powder is quartz, and the variation trend of its through porosity and interception layer thickness is the same as that of diatomite. The mechanical strength of the double-layer porous ceramic plate prepared by using the first ceramic powder with different mesh sizes does not change much.

[0098] In order to reduce the risk of damage, the mechanical strength should preferably be above 1.5Mpa. Under the premise that the mechanical strength can meet the requirements, generally speaking, the higher the through-porosity, the less likely it is to be blocked and the higher the filtration flux. The smaller the proportion of through holes in the interception layer whose pore size is larger than the preset filter pore size, the more difficult it is for solid particles exceeding the preset particle size to pass through the interception layer. Therefore, the proportion of through holes in the interception layer whose pore size is larger than the preset filter pore size is preferably less than 1%. In addition, if the particle size of the first ceramic powder is too large, the bubbles formed may be irregular and not uniform, resulting in problems of inconsistent local mechanical strength; if the particle size is too small, the grinding requirements are high and the cost is also high, but the improvement of the through-porosity is not large; therefore, the mesh number of the first ceramic powder is preferably 300-500 mesh, and more preferably about 400 mesh.

[0099] Figure 7-Figure 9 The schematic diagram shows the use of the double-layer porous ceramic plate prepared in Example C3 to filter the emulsified wastewater containing solid particles produced by the grinding machine. Figure 7 This is the particle size distribution diagram of solid particles in the sewage before filtration, where the concentration of solid particles in the wastewater before filtration is 338 mg / L. Figure 8 The backwashing time is 30 minutes after the experiment starts. In specific applications, the backwashing time can be selected according to actual needs. Figure 8 When the filtration flux drops to about 60% of the initial filtration flux, a backwash is performed. Figure 8 It can be seen that when using the double-layer porous ceramic plate for filtration, the filtration flux decreases over time, but after backwashing, the filtration flux is restored. Fig. 9 The left picture shows the sewage before filtration. Fig. 9 The picture on the right is a photo of the sewage after filtration. It can be seen intuitively from the picture that before filtration, the sewage was turbid because it contained more solid particles. After filtration, the sewage became clear.

[0100] The inventors of the present disclosure further discovered through experiments that although the double-layer porous ceramic plates prepared using different ceramic powders have similarities in material structure, due to the differences in the properties of different materials, the double-layer porous ceramic plates prepared using ceramic powders of different materials have differences in service life. Fig.10 The pure water flux test of the double-layer porous ceramic plates prepared using Example B3 and Example C3 is shown, and the pure water flux obtained under the same test conditions changes with time. From the figure, it can be seen that the pure water flux of the double-layer porous ceramic plate prepared by diatomaceous earth drops rapidly after being used for more than 16 hours; while the pure water flux of the double-layer porous ceramic plate prepared by quartz remains stable even after being used for more than 72 hours. It was observed that after being soaked in water for a long time, the double-layer porous ceramic plate prepared by diatomaceous earth expanded, resulting in blockage of the through holes, thereby causing a decrease in water flux, while the double-layer porous ceramic plate prepared by quartz did not expand, so that a stable flux could be maintained for a long time.

[0101] The disclosed method for preparing a double-layer porous ceramic plate is based on the foaming ceramic process. By using oil paper on the surface of the mold to prepare the blank, an extremely thin surface layer with pores, i.e., an interception layer, is formed on the surface of the prepared ceramic blank. Due to the foaming process, a supporting layer with a cavity structure having a large number of voids is formed inside the ceramic blank, so that the small-diameter pores of the interception layer can quickly transition to large-diameter cavities. The double-layer porous ceramic plate prepared by this method is not prone to clogging when used to filter sewage containing solid particles.

[0102] On the basis of the prepared ceramic rough blank, dry powder is further used to fill the pores of the interception layer of the ceramic rough blank, so that without increasing the thickness of the interception layer, the number of pores in the interception layer of the ceramic rough blank with a pore size larger than the preset filter pore size is greatly reduced, the number of large-sized solid particles passing through the interception layer is reduced, and the filtration effect is improved.

[0103] In addition, since the double-layer porous ceramic plate disclosed in the present invention has an extremely thin interception layer, and the through-holes of the interception layer have a small aperture, and the supporting layer has a large-sized cavity structure, the solid particles attached to the through-holes of the interception layer can be removed by backwashing the double-layer porous ceramic plate after being used for a period of time, and the filtration flux can be restored. Therefore, the double-layer porous ceramic plate disclosed in the present invention can be used repeatedly, thereby reducing the cost of sewage filtration and improving the efficiency of sewage filtration.

[0104] In addition, the present disclosure further selects quartz ceramic powder as the basic material to obtain a double-layer porous ceramic plate with stable physical properties and long-term use, making the present invention suitable for large-scale industrial applications.

[0105] A person skilled in the art can understand and implement other changes to the disclosed embodiments by reading the specification, the disclosed content, the drawings and the attached claims, and they all fall within the scope of protection of the claims of the present disclosure without departing from the essence of the claims of the present disclosure.

Claims

1. A method for preparing a double-layer porous ceramic plate, characterized in that: The method comprises the following steps: S1, stirring and mixing the first ceramic powder, water, adhesive and foam stabilizer to form a first mixed slurry; S2, adding a foaming agent to the first mixed slurry and stirring to form a foam slurry; S3, injecting the foam slurry into at least one mold covered with oil paper, and taking out the ceramic rough embryo after natural drying, wherein the contact surface between the ceramic rough embryo and the oil paper forms an interception layer; S4, filling the pores of the intercepting layer of the ceramic rough blank with a second ceramic powder dry powder to form a ceramic blank; S5, calcining the ceramic blank, heating the temperature to 900-1300° C. at a heating rate of 4-10° C. / min, and keeping the temperature for 1-5 hours to obtain the double-layer porous ceramic plate; The raw materials of the foam slurry are as follows in terms of mass percentage: 38-60% of the first ceramic powder, 32-60% of the water, 0.5-3% of the adhesive, 0.5-3% of the foam stabilizer, and 1-2% of the foaming agent.

2. The preparation method according to claim 1, characterized in that: The raw materials of the foam slurry are as follows in terms of mass percentage: the first ceramic powder is 48-52%, the water is 42-50%, the adhesive is 0.5-2%, the foam stabilizer is 0.5-2%, and the foaming agent is 1-2%.

3. The preparation method according to claim 1, wherein the mesh size of the first ceramic powder is 150-550 mesh.

4. The preparation method according to claim 1, characterized in that: The first ceramic powder and the second ceramic powder are any one or more of quartz, diatomaceous earth, mullite, kaolin, sepiolite, and dolomite.

5. The preparation method according to claim 4, characterized in that: The first ceramic powder and the second ceramic powder are both quartz.

6. The preparation method according to claim 1, characterized in that: The adhesive is any one or more of sodium carboxymethyl cellulose, hydroxyethyl cellulose, xanthan gum and gelatin.

7. The preparation method according to claim 1, characterized in that: The foaming agent is any one or more of sodium dodecyl sulfate, lauroyl diethanolamine, sodium dodecylaminopropionate, triethanolamine lauryl sulfate, and carbonates.

8. The preparation method according to claim 1, characterized in that: The foam stabilizer is any one or more of polyvinyl alcohol, modified starch, silicone resin polyether emulsion.

9. A double-layer porous ceramic plate prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the double-layer porous ceramic plate prepared by the preparation method according to any one of claims 1 to 8 in filtering sewage containing solid particles.

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