Formula and process for preparing gradient pore water storage ceramic by sintering fly ash and magnesium silicate sludge

Abstract

The invention relates to the technical field of solid waste resource utilization and porous ceramic material preparation, and discloses a formula and process for preparing gradient pore water storage ceramic through sintering of fly ash and magnesium silicate sludge, raw materials comprise fly ash, magnesium silicate mineralization powder, silicon carbide and a variable valence metal regulating agent. The process comprises ball milling activation, forming and dynamic decoupling gradient sintering. The chemical switching effect of the variable valence metal regulating agent is utilized, surface layer hole sealing is preferentially catalyzed in the low-temperature oxidation stage, and a compact oxidation barrier layer is constructed; and passivating the catalyst by using an internal anoxic environment, delaying an internal foaming reaction to a high-temperature matrix softening region, and forming pores and precipitating a cordierite crystal phase in situ by using a solid-phase oxidation-reduction reaction. According to the invention, a continuous gradient structure with compact protection outside and porous water storage inside is spontaneously constructed under a homogeneous batching system, the problem that the porosity and strength of the traditional foamed ceramic are mutually restricted is solved, and high-value utilization of multi-source solid waste is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of solid waste resource utilization and porous ceramic material preparation, in particular to a formula and process for sintering fly ash and magnesium silicate sludge to prepare gradient-pore water storage ceramics. BACKGROUND

[0002] Preparation of water storage ceramics from industrial solid wastes such as fly ash is an important approach to sponge city construction, but existing technologies still have deficiencies in balancing high porosity and mechanical strength. Although the physical layering process attempts to solve this contradiction by building a composite structure, due to the difficulty in completely matching the thermal expansion coefficients and shrinkage rates between different layers, stress concentration is easily generated at the macroscopic interface during sintering, leading to interlayer cracking or peeling of the product, seriously affecting the integrity and durability of the material.

[0003] At the same time, conventional fly ash-based ceramics usually have quartz, feldspar or mullite as the main crystal phase, with a relatively high thermal expansion coefficient. Under the action of repeated dry-wet cycles and day-night temperature differences in outdoor environments, due to the lack of low-expansion mineral phases for buffering, thermal stress damage is easily generated inside the material, resulting in poor thermal shock resistance and difficulty in meeting long-term service requirements.

[0004] In addition, the existing sintering process cannot precisely control the timing matching of surface sealing and internal foaming. If the surface densification lags behind, a large amount of internal gas will escape, causing the structure to collapse; for thick-walled products, the external atmosphere cannot effectively penetrate to the core area, and simply relying on external environmental control cannot ensure the uniform progress of internal foaming reactions, often resulting in internal structural defects due to insufficient internal oxygen source or pressure imbalance. SUMMARY

[0005] To overcome the deficiencies of the prior art, the present application provides a formula and process for sintering fly ash and magnesium silicate sludge to prepare gradient-pore water storage ceramics, which solves the problems of interface cracking caused by physical layering process, poor thermal shock resistance due to lack of low-expansion mineral phases, and difficulty in synchronously controlling the timing of surface sealing and internal foaming, resulting in internal structural defects.

[0006] To solve the above problems, the present application provides the following technical solutions:

[0007] In a first aspect, the present application provides a fly ash and magnesium silicate sludge sintered gradient-pore water storage ceramic, which adopts the following technical solutions:

[0008] Fly ash and magnesium silicate sludge sintered gradient-pore water storage ceramic, which is made from raw materials containing the following dry basis mass percentages:

[0009] Fly ash substrate powder: 55.0wt%-75.0wt%;

[0010] Magnesium silicate mineralized powder: 15.0wt%-30.0wt%;

[0011] Silicon carbide foaming powder: 3.0wt%-10.0wt%;

[0012] Variable valence metal regulator: 1.0wt%-6.0wt%;

[0013] The raw materials are additionally added with an organic binder, and the amount of the organic binder is 2.0wt%-5.0wt% of the total mass of the four raw materials.

[0014] By adopting the technical scheme, the present application realizes the space-time separation of reaction kinetics in a homogeneous material system by using the difference in the thermal chemical characteristics of each component, and the specific principle is as follows:

[0015] Variable valence metal catalytic oxidation characteristics: the variable valence metal oxides such as copper oxide or manganese dioxide in the formula have the effect of reducing the oxidation activation energy of silicon carbide at a low-temperature oxidation atmosphere. In the initial stage of sintering and heating, the surface layer of the variable valence metal maintains a high oxidation state, promotes the preferential reaction of the surface layer of silicon carbide and the magnesium silicate mineralized powder, and the generated low eutectic point liquid phase rapidly fills the intergranular gap.

[0016] In-situ formation of an oxidation barrier layer: the above-mentioned surface layer reaction product constructs a dense glass phase barrier layer in-situ on the surface of the ceramic body. The barrier layer blocks the diffusion channel of external oxygen to the interior of the body, and forces the establishment of a microenvironment with low oxygen partial pressure in the interior of the body.

[0017] Internal reaction kinetics inhibition: in the internal oxygen-poor environment, the variable valence metal oxides are reduced to low-valence states with lower catalytic activity (such as Cu 2+ Cu + or Cu), thereby inhibiting the oxidation rate of the internal silicon carbide. The difference in reaction activity delays the internal foaming reaction to the high-temperature stage when the matrix is completely softened.

[0018] High-temperature solid-phase pore formation and matrix strengthening: when the temperature reaches above the softening point of the matrix, the internal silicon carbide and the iron oxide in the fly ash undergo a solid-phase oxidation-reduction reaction to produce gas, which expands to form a closed pore structure under the physical restraint of the dense surface layer; at the same time, the magnesium silicate component reacts with the alumino-silicate to precipitate cordierite crystal phase, thereby enhancing the mechanical properties of the porous framework through crystal phase strengthening.

[0019] Preferably, the fly ash matrix powder is F-type or C-type fly ash.

[0020] By adopting the technical scheme, the F-class or C-class fly ash provides an aluminosilicate glass network framework. Preferably, the sum of the mass of the silicon dioxide and the aluminum oxide in the fly ash is not less than 70%, and the fly ash contains 3.0 wt%-8.0 wt% of the iron oxide. The iron oxide, as a key solid-phase oxidant in the internal high-temperature stage, reacts with the silicon carbide (Fe2O3+SiC→FeO+SiO2+CO2 / CO), to ensure that sufficient gas is generated internally after the external oxygen source is cut off. At the same time, the median particle size D50 of the fly ash is controlled to be 10 μm-45 μm, to balance the reaction activity and the green body bulk density.

[0021] Preferably, the magnesium silicate mineralized powder is an industrial sludge rich in magnesium silicate, which is dried to constant weight at 105°C-150°C, crushed, and sieved.

[0022] By adopting the technical scheme, the magnesium oxide (content ≥ 15%) in the raw material reacts with the aluminum and silicon components in the fly ash to generate cordierite (2MgO·2Al2O3·5SiO2) at high temperature. The low thermal expansion property of the cordierite can offset the internal stress generated by the porous structure when the temperature changes, improving the volume stability of the material, and realizing the resource utilization of the industrial sludge.

[0023] Preferably, the silicon carbide foaming micro-powder is an industrial-grade silicon carbide powder or a photovoltaic cutting waste mortar recycling powder; and the organic binder is a polyvinyl alcohol aqueous solution or a sodium carboxymethyl cellulose aqueous solution with a concentration of 5 wt%-10 wt%.

[0024] By adopting the technical scheme, the median particle size D50 of the silicon carbide is preferably 5 μm-25 μm, which matches the catalytic kinetics of the variable-valence metal regulator: avoiding the surface reaction from being too fast and not being sealed due to too small particle size, or the internal foaming from being uneven due to too large particle size. The organic binder provides strength at the low-temperature stage, and forms micro-pore channels after decomposition to assist the reaction mass transfer.

[0025] Preferably, the variable-valence metal regulator is selected from one or more of copper oxide, cuprous oxide, and manganese dioxide; or, the variable-valence metal regulator is prepared by calcining copper-containing electroplating sludge incineration slag at 400°C-450°C for 1.5h-2h, and then ball milling the cooled slag at a ball-to-material mass ratio of 3:1 and a rotation speed of 300 r / min-350 r / min for 4h-6h; or, the variable-valence metal regulator is prepared by drying waste zinc-manganese batteries recycling powder at 115°C-125°C for 3h-5h, and then grinding for 25min-35min.

[0026] By adopting the technical scheme, pure oxides or industrial waste residues rich in copper / manganese can be used. After calcination and impurity removal and mechanical ball milling and activation, the metals in the waste residues are converted into stable oxides or solid solutions. In the sintering process, these metal ions not only play a catalytic regulation role, but also are finally solid-solved in the glass phase or crystal lattice, realizing the solidification and storage of heavy metals. Mechanical activation increases the specific surface area of the regulating agent, ensures uniform dispersion of the regulating agent in the raw materials, and ensures consistency of the micro-area reaction kinetics.

[0027] In a second aspect, the application provides a preparation process for sintering fly ash and magnesium silicate sludge to prepare gradient-pore water storage ceramics, which adopts the following technical scheme:

[0028] The preparation process for sintering fly ash and magnesium silicate sludge to prepare gradient-pore water storage ceramics comprises the following steps:

[0029] S1: Ball-mill mix fly ash matrix powder, magnesium silicate mineralized powder, silicon carbide foaming powder, and variable-valence metal regulating agent to obtain a homogeneous mixture;

[0030] S2: Mix and granulate the homogeneous mixture with an organic binder, and press-form to obtain a ceramic green body;

[0031] S3: Place the ceramic green body in an oxidizing atmosphere for dynamic decoupling gradient sintering, which comprises a surface catalytic sealing stage, an internal catalyst passivation stage, and a high-temperature matrix foaming and mineralization stage in sequence;

[0032] S4: Cool the sintered product to obtain the gradient-pore water storage ceramics.

[0033] By adopting the above technical scheme, the chemical reaction rate is regulated by using a segmented heat treatment process to construct a self-generated gradient structure in the homogeneous body:

[0034] Surface catalytic sealing stage: In an oxidizing atmosphere, the surface layer of the body contacts oxygen. The high-valence variable-valence metal regulating agent (such as CuO) reduces the oxidation reaction energy barrier of the surface layer of silicon carbide, promoting its preferential oxidation at a temperature lower than the internal foaming temperature. The generated silicon dioxide forms a eutectic liquid phase with the matrix components, fills the surface layer pores, and constructs a dense glass phase oxidation barrier layer.

[0035] Internal catalyst passivation stage: With the formation of the barrier layer, the internal oxygen is depleted. In the oxygen-poor environment, the internal variable-valence metal regulating agent is reduced to a low-valence state (such as Cu2O or Cu) with lower catalytic activity. This process inhibits the low-temperature oxidation consumption of internal silicon carbide, keeps the internal foaming reaction kinetically inert during the temperature rise process, and realizes the decoupling of surface sealing and internal foaming.

[0036] High-temperature matrix foaming and mineralization stage: As the temperature rises to the melting and softening range of the matrix, thermal excitation causes the internal reaction to overcome the energy barrier. Silicon carbide and iron oxide undergo a solid-phase redox reaction, releasing gas, which forces the softened matrix to expand under the constraint of the dense surface layer, forming a honeycomb-like closed pore. At the same time, the magnesium silicate component undergoes a mineralization reaction, precipitating cordierite crystal phase.

[0037] Preferably, in step S3, the specific process parameters for kinetic decoupling gradient sintering are as follows: For the surface catalytic sealing stage: the temperature is increased to 900℃-950℃ at a rate of 3℃ / min-8℃ / min, and held for 30min-60min; For the internal catalyst passivation stage: the temperature is continuously increased from 950℃ to 1100℃ at a rate of 3℃ / min-5℃ / min; For the high-temperature matrix foaming and mineralization stage: the temperature is increased to 1150℃-1250℃ at a rate of 2℃ / min-3℃ / min, and held for 60min-120min.

[0038] By adopting the above technical solution, the parameters of each stage correspond to the thermodynamic window of the material reaction: 900℃-950℃ is the starting temperature zone for surface oxidation of variable valence metal catalyst, and heat preservation promotes the densification of the sealing layer; 950℃-1100℃ uses continuous heating to quickly cross the reduction temperature zone of the internal catalyst and prevent internal pre-oxidation; 1150℃-1250℃ is the temperature zone where the matrix viscosity is suitable for foaming and cordierite crystallization, and heat preservation ensures pore development and crystal phase precipitation.

[0039] Preferably, in step S1, the ball-to-material mass ratio of the ball milling mixture is (2-3):1, the rotation speed is 250 r / min-350 r / min, the time is 4 h-8 h, and the specific surface area of ​​the homogeneous mixture is controlled to be 400 m². 2 / kg-600m 2 / kg.

[0040] By employing the above technical solution, mechanical ball milling disrupts the surface lattice of raw material particles, increasing the number of reactive sites. The specific surface area is controlled at 400 m². 2 / kg-600m 2 / kg, ensuring that the variable valence metal modifier is uniformly coated on silicon carbide particles at the microscale is a prerequisite for achieving overall kinetic control, while avoiding molding difficulties caused by excessively fine powder.

[0041] Preferably, in step S2, the pressing pressure is 20MPa-40MPa, and the holding time is 10s-30s.

[0042] By employing the above technical solution, the forming pressure ensures that the green body has suitable particle contact. Close particle contact facilitates liquid-phase mass transfer and sintering neck formation, promoting the rapid construction of a tightly sealed pore layer on the surface. The pressure parameters are set to balance the sealing requirements with the venting requirements of the organic binder.

[0043] Preferably, in step S4, the cooling includes a rapid cooling stage and a natural cooling stage, specifically: rapidly cooling from high temperature to 800°C at a rate of 5°C / min-10°C / min, and then naturally cooling to room temperature with the furnace.

[0044] By employing the above technical solution, the rapid cooling process is used to fix the porous framework formed at high temperatures. Rapid cooling to below the glass transition temperature (800℃) prevents pore collapse or backflow caused by reduced liquid phase viscosity and inhibits the precipitation of high-expansion-coefficient crystalline phases (such as anorthite), ensuring the dimensional accuracy and mechanical properties of the product.

[0045] This invention provides a formula and process for preparing gradient pore water storage ceramics by sintering fly ash in conjunction with magnesium silicate sludge. It has the following beneficial effects:

[0046] 1. This invention constructs a kinetic decoupling mechanism using a variable-valence metal regulator, leveraging its catalytic activity differences under varying oxygen partial pressures to achieve spatiotemporal separation of low-temperature surface sealing and high-temperature internal foaming in a single homogeneous system. This approach successfully prepares gradient-structured ceramics that combine surface protection and internal water storage functions, effectively resolving the contradiction between porosity and mechanical strength in traditional foamed ceramics.

[0047] 2. This invention utilizes magnesium-rich industrial sludge and fly ash to generate cordierite crystalline phases with low expansion coefficients in situ, constructing a microscopic reinforcing framework. This mineral phase structure improves the material's thermal shock resistance and volume stability, while simultaneously realizing the resource utilization and high-value-added utilization of bulk industrial solid waste.

[0048] 3. This invention utilizes the inherent iron oxide in fly ash as a solid-phase oxygen source for internal foaming. After the dense surface layer cuts off external oxygen, it drives an internal solid-phase redox reaction to release gas. This mechanism eliminates dependence on the external sintering atmosphere, ensuring the formation of a uniform and interconnected honeycomb-like closed-cell structure in a closed, oxygen-deficient environment, thus preventing structural collapse. Detailed Implementation

[0049] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to comparative examples and test cases. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0050] Preparation Examples 1-6:

[0051] Preparation Example 1: Magnesium-rich tailings mud from the aforementioned copper mine tailings pond was placed in a forced-air drying oven at a drying temperature of 105°C and dried to constant weight (moisture content ≤2%). The dried mud blocks were fed into a jaw crusher for coarse crushing, then pulverized by a pulverizer and passed through a 100-mesh sieve. The undersize powder was collected to obtain magnesium silicate mineralized powder A.

[0052] Preparation Example 2: Take the magnesium-rich tailings mud from the aforementioned copper mine tailings pond, place it in a rotary kiln, set the drying temperature to 128℃, and dry it to constant weight (moisture content ≤2%); send the dried mud blocks into a jaw crusher for coarse crushing, then crush them through a pulverizer and pass them through a 100-mesh sieve, collect the powder under the sieve, and obtain magnesium silicate mineralized powder B.

[0053] Preparation Example 3: Take the magnesium-rich tailings mud from the aforementioned copper mine tailings pond, place it in a belt dryer, set the drying temperature to 150℃, and dry it to constant weight (moisture content ≤2%); send the dried mud blocks into a jaw crusher for coarse crushing, then crush them through a pulverizer and pass them through a 100-mesh sieve, collect the powder under the sieve, and obtain magnesium silicate mineralized powder C.

[0054] Preparation Example 4: The aforementioned copper-containing electroplating sludge incineration residue was placed in a muffle furnace and calcined at 400°C for 2 hours to remove residual organic matter; after cooling, it was placed in a planetary ball mill, using zirconia balls as the medium, with a ball-to-material mass ratio of 3:1, a rotation speed of 300 r / min, and ball milling for 4 hours; after discharge, the median particle size D50 was measured by a laser particle size analyzer and found to be 4.5 μm, thus obtaining the variable valence metal regulator D.

[0055] Preparation Example 5: The aforementioned copper-containing electroplating sludge incineration residue was placed in a muffle furnace and calcined at 450°C for 1.5 hours; after cooling, it was placed in a planetary ball mill, using zirconia balls as the medium, with a ball-to-material mass ratio of 3:1, a rotation speed of 350 r / min, and ball milling for 6 hours; after discharge, the material was detected by a laser particle size analyzer, and the median particle size D50 was 3.2 μm, thus obtaining the variable valence metal regulator E.

[0056] Preparation Example 6: Commercially available waste zinc-manganese battery recycled powder (of which the manganese dioxide content was tested to be 41.0%) was placed in an oven and dried at 120°C for 4 hours to remove adsorbed water; then it was placed in a vibration mill and ground for 30 minutes; after discharge, the median particle size D50 was measured by a laser particle size analyzer and was 3.8 μm, thus obtaining variable valence metal regulator F.

[0057] Examples 1-3:

[0058] Example 1: This example provides a gradient pore water storage ceramic prepared by sintering fly ash and magnesium silicate sludge. The preparation process includes the following steps:

[0059] Based on the total dry weight percentage, weigh 75.0% of fly ash matrix powder, 21.0% of magnesium silicate mineralization powder A provided in Preparation Example 1, 3.0% of silicon carbide foamed micro powder, and 1.0% of commercially available analytical grade copper oxide powder (as a variable valence metal modifier); in addition, weigh an additional 2.0% of organic binder equivalent to the total mass of the above inorganic dry materials.

[0060] The four weighed powders were placed into a ball mill, the ball-to-powder mass ratio was set to 2:1, the rotation speed was 250 r / min, and ball milling activation was performed for 4 hours to obtain a specific surface area of ​​420 m². 2 / kg of homogeneous mixture.

[0061] The homogeneous mixture and organic binder are mixed and granulated in a granulator, and the moisture content of the granulated powder is controlled at 6.5%. The mixture is then sealed and aged for 12 hours. Subsequently, it is pressed under a pressure of 40 MPa and held for 30 seconds to obtain a ceramic green body.

[0062] Kinetic decoupled gradient sintering: The ceramic green body is placed in a roller kiln with an oxidizing atmosphere; firstly, the temperature is raised to 900℃ at a rate of 5℃ / min and held for 60min (stage A), using copper oxide to catalyze the formation of an oxide barrier layer on the surface silicon carbide; then, the temperature is continuously raised to 1000℃ at a rate of 3℃ / min (stage B), during which the internal copper oxide is reduced, inhibiting internal foaming; finally, the temperature is raised to 1150℃ (Tmax) at a rate of 2℃ / min and held for 120min (stage C), causing a solid-phase redox reaction to occur inside, generating pores and forming cordierite crystal phase.

[0063] After sintering, the temperature is rapidly cooled to 800°C at a rate of 5°C / min, and then naturally cooled to room temperature in the furnace to obtain gradient pore water storage ceramic.

[0064] Example 2: This example provides a gradient pore water storage ceramic prepared by sintering fly ash and magnesium silicate sludge. The preparation process includes the following steps:

[0065] Based on the total dry weight percentage, 65.0% of fly ash matrix powder, 26.0% of magnesium silicate mineralization powder B provided in Preparation Example 2, 6.0% of silicon carbide foamed micro powder, and 3.0% of variable valence metal regulator D (copper-based waste residue source) provided in Preparation Example 4 were weighed; in addition, an organic binder equivalent to 3.0% of the total mass of the above inorganic dry materials was weighed.

[0066] The four weighed powders were placed into a ball mill, the ball-to-powder mass ratio was set to 2.5:1, the rotation speed was 300 r / min, and ball milling activation was carried out for 6 hours to obtain a specific surface area of ​​510 m². 2 / kg of homogeneous mixture.

[0067] The homogeneous mixture and organic binder are mixed and granulated in a granulator, and the moisture content of the granulated powder is controlled at 7.0%. The mixture is then sealed and aged for 18 hours. Subsequently, it is pressed under a pressure of 30 MPa and held for 20 seconds to obtain a ceramic green body.

[0068] The ceramic green body is placed in a shuttle kiln under an oxidizing atmosphere. First, the temperature is raised to 925℃ at a rate of 6℃ / min and held for 45min (stage A) to establish a dense surface shell. Then, the temperature is continuously raised to 1050℃ at a rate of 4℃ / min (stage B) to passivate the internal catalyst using a reducing atmosphere. Finally, the temperature is raised to 1200℃ (Tmax) at a rate of 2.5℃ / min and held for 90min (stage C) to complete the internal pore formation and matrix mineralization.

[0069] After sintering, the temperature is rapidly cooled to 800°C at a rate of 8°C / min, and then naturally cooled to room temperature in the furnace to obtain gradient pore water storage ceramic.

[0070] Example 3: This example provides a method for preparing gradient pore water storage ceramics by sintering fly ash in conjunction with magnesium silicate sludge. The preparation process includes the following steps:

[0071] Based on the total dry weight percentage, 55.0% of fly ash matrix powder, 29.0% of magnesium silicate mineralization powder C provided in Preparation Example 3, 10.0% of silicon carbide foamed micro powder, and 6.0% of variable valence metal regulator E (copper-based waste residue source) provided in Preparation Example 5 were weighed; in addition, an organic binder equivalent to 5.0% of the total mass of the above inorganic dry materials was weighed.

[0072] The four weighed powders were placed in a ball mill, the ball-to-powder mass ratio was set to 3:1, the rotation speed was 350 r / min, and ball milling activation was performed for 8 hours to obtain a specific surface area of ​​580 m². 2 kg of homogeneous mixture.

[0073] The homogeneous mixture and organic binder are mixed and granulated in a granulator, and the moisture content of the granulated powder is controlled at 8.0%. The mixture is then sealed and aged for 24 hours. Subsequently, it is pressed under a pressure of 20 MPa and held for 10 seconds to obtain a ceramic green body.

[0074] The ceramic green body is placed in a kiln with an oxidizing atmosphere; first, the temperature is raised to 950℃ at a rate of 8℃ / min and held for 30min (stage A) to quickly form a thicker oxide barrier layer; then, the temperature is continuously raised to 1100℃ at a rate of 5℃ / min (stage B); finally, the temperature is raised to 1250℃ (Tmax) at a rate of 3℃ / min and held for 60min (stage C) to achieve high porosity foaming at high temperature.

[0075] After sintering, the temperature is rapidly cooled to 800°C at a rate of 10°C / min, and then naturally cooled to room temperature in the furnace to obtain gradient pore water storage ceramic.

[0076] Example 4: This example provides a gradient pore water storage ceramic prepared by sintering fly ash and magnesium silicate sludge. The preparation process includes the following steps:

[0077] Based on the total dry weight percentage, 65.0% of fly ash matrix powder, 26.0% of magnesium silicate mineralization powder B provided in Preparation Example 2, 6.0% of silicon carbide foamed micro powder, and 3.0% of variable valence metal regulator F (manganese-based waste residue source) provided in Preparation Example 6 were weighed out; in addition, an organic binder equivalent to 3.0% of the total mass of the above inorganic dry materials was weighed out. (Note: In this example, except that the variable valence metal regulator D is replaced with the variable valence metal regulator F, all other formulation ratios are completely consistent with those in Example 2).

[0078] The process parameters for ball milling activation were the same as in Example 2 (ball-to-material mass ratio 2.5:1, rotation speed 300 r / min, time 6 h).

[0079] The granulation process parameters were kept the same as in Example 2 (moisture content 7.0%, pressure 30 MPa).

[0080] The kinetic decoupling gradient sintering process parameters were kept consistent with those of Example 2 (Stage A was held at 925℃ for 45 min; Stage B was continuously heated; Stage C was held at 1200℃ for 90 min).

[0081] The cooling and shaping process parameters are consistent with those in Example 2.

[0082] Comparative Examples 1-5:

[0083] Comparative Example 1: Compared with Example 2, the difference is that the variable valence metal regulator D is not added, and its 3.0 wt% mass share is made up by fly ash matrix powder (the amount of fly ash matrix powder is adjusted to 68.0 wt%). The other raw material components and preparation process parameters are the same.

[0084] Comparative Example 2: Compared with Example 2, the difference is that 3.0 wt% of the variable valence metal modifier D was replaced with an equal mass of zinc oxide powder, while the other raw material components and preparation process parameters were the same.

[0085] Comparative Example 3: Compared with Example 2, the difference is that the step of holding at 925℃ for 45 minutes in the sintering process is omitted. After the ceramic green body is placed in the kiln, it is directly heated from room temperature to 1200℃ at an average heating rate of 4℃ / min. The other raw material components and pretreatment processes are the same.

[0086] Comparative Example 4: Compared to Example 2, the difference lies in the use of a layered fabric pressing molding process. The raw materials are divided into two parts: the first part is a top layer material without silicon carbide foaming micropowder (fly ash / magnesium silicate / regulator / binder mixed according to the proportions of Example 2), and the second part is a bottom layer material containing silicon carbide foaming micropowder (mixed according to the full formula of Example 2). During pressing, the top layer material is first laid into the bottom of the mold (accounting for 20% of the total mass), and then the bottom layer material (accounting for 80% of the total mass) is laid in, and the molding is carried out in one step at 30 MPa. The sintering process parameters are the same as those of Example 2.

[0087] Comparative Example 5: Compared with Example 2, the difference is that 6.0 wt% of silicon carbide foamed micro powder was replaced with an equal mass of activated carbon powder (particle size D50 of 15 μm), while the other raw material components and preparation process parameters were the same.

[0088] Test Example 1-2:

[0089] Test Example 1: Conventional Physical and Mechanical Performance Tests

[0090] Experimental description:

[0091] This test characterizes the physical properties and mechanical strength of the ceramic samples prepared in Examples 1 to 4 and Comparative Examples 1 to 5. The testing process strictly follows the national standard method for ceramic tiles, and the specific steps are as follows:

[0092] Determination of water absorption, apparent porosity and bulk density:

[0093] The test was conducted using the vacuum method, in accordance with standard GB / T 3810.3-2016, Test Methods for Ceramic Tiles.

[0094] The sintered sample was cut into 50mm×50mm blocks, dried in an oven at 110℃ until constant weight, and the dry weight (M1) was measured.

[0095] Place the test block in a vacuum device, evacuate to a residual pressure of less than 2.0 kPa and maintain for 15 min, then inject distilled water to submerge the test block, restore normal pressure and let it stand for 30 min.

[0096] The suspended mass (M2) of the test block in water was measured using a hydrostatic balance.

[0097] Remove the test block, wipe off the water adhering to the surface with a damp cloth, and weigh the saturated mass (M3).

[0098] The bulk density, apparent porosity, and water absorption rate were calculated using Archimedes' principle.

[0099] Compressive strength determination:

[0100] Tests were performed using a hydraulic universal testing machine. The reference standard was GB / T 3810.4-2016, Test Methods for Ceramic Tiles (since this product is a block-type water-retaining ceramic, the loading method in the flexural strength standard was adjusted to compressive strength test).

[0101] The sample was processed into a cubic block of 50mm×50mm×50mm.

[0102] Ensure the pressure surface is flat, apply load at a loading rate of 0.5 MPa / s until the specimen fails, and record the maximum failure load F.

[0103] The compressive strength is calculated using the formula P = F / S (where S is the area under pressure).

[0104] Test results:

[0105] The specific test data for each group of samples are shown in the table below:

[0106] Table 1. Summary of physical and mechanical properties of each example and comparative sample

[0107]

[0108]

[0109] Results Analysis and Conclusions:

[0110] The apparent porosity and compressive strength data of Examples 1 to 4 show that a balance between high porosity and high strength can be achieved in a single homogeneous feedstock system by using a variable valence metal regulator in conjunction with a segmented sintering process. The data for Examples 2 and 4 are similar, confirming that both copper-based and manganese-based regulators can achieve kinetic decoupling. Comparative Examples 1 (without regulator) and 3 (direct sintering) have low apparent porosity (21.5% and 23.8%, respectively), indicating a lack of catalytic sealing or failure to maintain a specific temperature range, leading to significant gas escape and ineffective pore formation. Comparative Example 2 (constant valence zinc oxide) has a certain apparent porosity, but low closed porosity and a strength of only 6.8 MPa, indicating that overlapping surface sealing and internal foaming leads to structural defects. The compressive strength (8.4 MPa) of Comparative Example 4 (physical layering) is lower than that of Example 2 (16.8 MPa) with the same composition, indicating that the integrally formed gradient structure has superior mechanical load-bearing capacity compared to the physically layered structure.

[0111] Test Example 2: Gradient Structure Characteristics and Compactness Verification Test

[0112] Experimental description:

[0113] This test aims to verify whether the sintered product has formed the expected continuous gradient structure and to assess the integrity of its structure. The test employs a combination of red ink penetration and cross-sectional macroscopic observation. The specific operational steps are as follows:

[0114] Sample preparation and cutting:

[0115] Three samples were randomly selected from each of the sintered products of Examples 1 to 4 and Comparative Examples 1 to 5. Using a precision cutter equipped with a diamond saw blade, the samples were cut in half along a direction perpendicular to the pressure surface to obtain a longitudinal section exposing the central region. After cutting, the cross-section was cleaned with an ultrasonic cleaner to remove cutting dust and then dried in an oven at 105°C for 30 minutes.

[0116] Red ink penetration experiment:

[0117] Place the dried sample, cross-section facing down, into a shallow dish containing standard red ink, ensuring the immersion depth is half the height of the cross-section, and maintain immersion time for 10 minutes. Alternatively, use the direct application method: apply red ink evenly to the entire cross-section with a brush and let it stand for 5 minutes.

[0118] Rinsing and observation:

[0119] Remove the sample and quickly rinse the cross-section surface with running water to remove any unabsorbed surface dye. Then, blot the surface dry with absorbent paper. Observe the staining of the cross-section under natural light using the naked eye and a 5x magnifying glass. Focus on recording the unstained thickness (i.e., the thickness of the dense layer) of the surface layer (from the outer edge inward), the staining depth and pore distribution in the internal area, and the presence of transverse or longitudinal structural cracks.

[0120] Test results:

[0121] The cross-sectional structural characteristics and permeability test results of samples from each group are recorded in the table below:

[0122] Table 2. Cross-sectional structural characteristics of samples from each group and observation records of red ink penetration.

[0123]

[0124]

[0125] Results Analysis and Conclusions:

[0126] Cross-sectional observations show that Examples 1 to 4 all formed a gradient structure with a dense, non-absorbent outer layer and a porous, ink-absorbent inner layer, with no physical interface between the surface and the interior, exhibiting a continuous transition. Comparative Examples 1 and 3, lacking an effective catalytic sealing mechanism or process control, failed to form a dense surface layer, resulting in overall or partial penetration of red ink. Comparative Example 4 showed ink deposition lines and microcracks at the interface, confirming interfacial stress defects in the physical layering process. The irregular pore morphology of Comparative Examples 2 and 5 indicates that constant-valence oxides or activated carbon cannot match the kinetic window of matrix softening and sealing. Experiments confirm that the self-gradient structure constructed using chemical kinetic differences in this invention has better structural integrity and density.

Claims

1. A gradient pore water-storage ceramic prepared by sintering fly ash and magnesium silicate sludge, characterized in that, Made from raw materials comprising the following dry basis weight percentages: Fly ash matrix powder: 55.0wt%-75.0wt%; Magnesium silicate mineralized powder: 15.0wt%-30.0wt%; Silicon carbide foamed micro powder: 3.0wt%-10.0wt%; Variable valence metal modifier: 1.0wt%-6.0wt%; The organic binder is used in an amount of 2.0 wt% to 5.0 wt% of the total mass of the fly ash matrix powder, the magnesium silicate mineralization powder, the silicon carbide foamed micro powder, and the variable valence metal regulator.

2. The gradient pore water storage ceramic prepared by sintering fly ash and magnesium silicate sludge according to claim 1, characterized in that, The fly ash matrix powder is either type F or type C fly ash.

3. The gradient pore water storage ceramic prepared by sintering fly ash and magnesium silicate sludge according to claim 1, characterized in that, The magnesium silicate mineralized powder is a powder obtained by drying industrial sludge rich in magnesium silicates at 105℃-150℃ to constant weight, crushing and sieving.

4. The gradient pore water-storage ceramic prepared by sintering fly ash and magnesium silicate sludge according to claim 1, characterized in that, The silicon carbide foamed micro powder is industrial-grade silicon carbide powder or recycled photovoltaic cutting waste slurry powder, and the organic binder is a 5wt%-10wt% aqueous solution of polyvinyl alcohol or sodium carboxymethyl cellulose.

5. The gradient pore water-storage ceramic prepared by sintering fly ash and magnesium silicate sludge according to claim 1, characterized in that, The variable valence metal regulator is selected from one or more of copper oxide, cuprous oxide, and manganese dioxide. Alternatively, the variable valence metal regulator can be obtained by calcining copper-containing electroplating sludge incinerator residue at 400℃-450℃ for 1.5h-2h, cooling it, and then ball milling it at a ball-to-material mass ratio of 3:1 and a rotation speed of 250r / min-350r / min for 4h-6h. Alternatively, the variable valence metal regulator can be obtained by drying waste zinc-manganese battery recycled powder at 115℃-125℃ for 3h-5h, followed by grinding for 25min-35min.

6. A preparation process for gradient porous water-storing ceramics prepared by sintering fly ash and magnesium silicate sludge, characterized in that, The method for preparing gradient pore water-storing ceramics by sintering fly ash and magnesium silicate sludge as described in any one of claims 1 to 5 comprises the following steps: S1: The fly ash matrix powder, magnesium silicate mineralization powder, silicon carbide foamed micro powder and variable valence metal regulator are ball-milled and mixed to obtain a homogeneous mixture; S2: The homogeneous mixture is mixed with an organic binder, granulated, and pressed to obtain a ceramic green body; S3: The ceramic green body is placed in an oxidizing atmosphere for kinetic decoupling gradient sintering, the sintering including a surface catalytic sealing stage, an internal catalyst passivation stage and a high-temperature matrix foaming and mineralization stage performed sequentially. S4: Cool the sintered product to obtain the gradient pore water storage ceramic.

7. The preparation process for gradient porous water-storing ceramics by sintering fly ash and magnesium silicate sludge according to claim 6, characterized in that, In step S1, the ball-to-material mass ratio of the ball mill mixture is (2-3):1, the rotation speed is 250 r / min-350 r / min, the time is 4 h-8 h, and the specific surface area of ​​the homogeneous mixture is controlled to be 400 m². 2 / kg-600m 2 / kg.

8. The preparation process for gradient porous water-storing ceramics by sintering fly ash and magnesium silicate sludge according to claim 6, characterized in that, In step S2, the pressing pressure is 20MPa-40MPa, and the pressing holding time is 10s-30s.

9. The preparation process for gradient porous water-storing ceramics by sintering fly ash and magnesium silicate sludge according to claim 6, characterized in that, In step S3, the specific process parameters for kinetic decoupling gradient sintering are as follows: During the surface catalytic sealing stage, the temperature is increased to 900℃-950℃ at a rate of 3℃ / min-8℃ / min and held for 30min-60min. During the internal catalyst passivation stage, the temperature is increased to 1000℃-1100℃ at a rate of 3℃ / min-5℃ / min. During the high-temperature matrix foaming and mineralization stage, the temperature is increased to 1150℃-1250℃ at a rate of 2℃ / min-3℃ / min and held for 60min-120min.

10. The preparation process for gradient porous water-storing ceramics by sintering fly ash and magnesium silicate sludge according to claim 6, characterized in that, In step S4, cooling includes a rapid cooling stage and a natural cooling stage, and the cooling process specifically involves: The temperature was rapidly cooled from high temperature to 750℃-850℃ at a rate of 5℃ / min-10℃ / min, and then naturally cooled to room temperature with the furnace.

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