Recycling treatment process for fly ash after chelating landfill

Abstract

The invention relates to the technical field of solid waste treatment processes, in particular to a recycling treatment process for chelated and buried fly ash. The process comprises the following steps: carrying out particle size control crushing on the embedded chelated fly ash; the method comprises the following steps: sequentially removing heavy metals with different valence states by adopting a three-stage pH-adjusting water washing system, and assisting with organic acid, a water-soluble silicon source, a calcium complex and a phosphate auxiliary agent to strengthen heavy metal stabilization and glass precursor structure construction; after dehydration, a conditioner, a fluxing filler and a pore-forming component are introduced to form a mixture; the porosity of the block is controlled through double-section pressure cold press molding; and carrying out segmented heating heat treatment and high-temperature melting and curing to obtain a final product with a compact structure and a uniform glass phase. The process can obviously reduce the leaching concentration of heavy metals and improve the density and the compression strength.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of solid waste treatment processes, in particular to a chelated post-landfill fly ash re-resource disposal process. BACKGROUND

[0002] Incineration fly ash is a fine particulate solid waste generated during municipal solid waste incineration treatment, usually enriched with heavy metal ions of multiple valence states and high content of soluble salts, which has potential harm to the ecological environment. In the prior art, in order to reduce the migration ability of heavy metals in fly ash, chemical chelation is often used for pretreatment, and complex structures are formed by adding chelating agents with heavy metal ions to stabilize their forms. This method can effectively reduce the leaching concentration of heavy metals in the short term and is widely used in fly ash pretreatment.

[0003] However, the chelated fly ash is limited by the initial process conditions and the stability of the chelating agent, and its long-term environmental behavior shows certain uncertainty. Especially after landfill or long-term stacking, the chelated heavy metals in the fly ash may gradually dissociate under the action of microorganisms or environmental pH fluctuations, thereby re-released into the environment, forming a secondary pollution risk. In addition, chelated fly ash usually shows loose particles, uneven particle size, and high water content in terms of physical structure, and is difficult to directly enter the melting or glassification process. Traditional solidification, melting or water washing methods often have high residual rate of heavy metals and insufficient leaching risk control ability when treating such chelated fly ash, and it is difficult to form a resource product with dense structure and high chemical stability.

[0004] Therefore, the prior art has the following technical problems in treating chelated fly ash: first, the long-term storage of chelated fly ash has the risk of re-releasing heavy metals, and the environmental stability is poor; second, the existing reprocessing means has insufficient adaptability in terms of structure densification control, heavy metal removal efficiency and glass network formation, and it is difficult to achieve stable and efficient resource utilization. SUMMARY

[0005] In view of the deficiencies in the prior art, the purpose of the present application is to provide a chelated post-landfill fly ash re-resource disposal process.

[0006] A chelated post-landfill fly ash re-resource disposal process, comprising the following steps: S1: crushing the chelated fly ash after landfill, and controlling the particle size of the fly ash particles obtained after crushing to be in the range of 5-20 mm.

[0007] S2: sequentially performing multi-stage water washing treatment on the crushed fly ash particles, the multi-stage water washing treatment comprising the following stages: S2.1: under the condition that the pH is 5.5-6.0, the fly ash is subjected to first water washing.

[0008] S2.2: The fly ash is washed with water for the second time under the condition that the pH is 7.0-7.5.

[0009] S2.3: The fly ash is washed with water for the third time under the condition that the pH is 9.0-10.0.

[0010] S3: The fly ash after water washing is subjected to dewatering treatment, so that the water content is controlled to be 15%-25%.

[0011] S4: The fly ash after dewatering, the residue in the filtrate generated in the water washing in the S2 step and auxiliary components are mixed to prepare a mixture; the auxiliary components include a silicon-aluminum conditioner, foam glass microbeads, starch and a polycarboxylic acid water reducer.

[0012] S5: The mixture is subjected to cold pressing to obtain a pressed block body with a porosity of 10%-25%.

[0013] S6: The pressed block body is subjected to heat treatment at 400-600°C to obtain a pre-sintered block body.

[0014] S7: The pre-sintered block body is subjected to melting treatment at 1200-1350°C, and after water quenching cooling, a stable glass body and / or mineral structure product is obtained.

[0015] Further, the mixture composed of 100 parts of the fly ash after dewatering in S3 and fly ash original fly ash subjected to three-stage countercurrent water washing, 5-15 parts of residue in the filtrate generated in the water washing in the S2 step, 10-25 parts of a silicon-aluminum conditioner, 1-3 parts of foam glass microbeads, 1-3 parts of starch and 0.2-0.5 parts of a polycarboxylic acid water reducer.

[0016] The fly ash original fly ash subjected to three-stage countercurrent water washing: the fly ash collected in a waste incineration flue gas system is subjected to A1: first water washing under the condition that the pH is 5.5-6.0.

[0017] A2: second water washing of the fly ash under the condition that the pH is 7.0-7.5.

[0018] A3: third water washing of the fly ash under the condition that the pH is 9.0-10.0.

[0019] A4: dewatering treatment so that the water content is controlled to be 20%-25%.

[0020] Further, the pH adjustment in the S2.1 step is performed by using an organic acid; the pH adjustment in the S2.2 step is performed by using an acid-base buffer system; and the pH adjustment in the S2.3 step is performed by using one or more of sodium hydroxide, sodium carbonate or sodium bicarbonate.

[0021] Further, a water-soluble silicon source additive is also added in the S2.1 step, which is sodium silicate or sodium metasilicate, and the dosage is controlled to be 0.5-2 wt% of the mass of the fly ash washed with water.

[0022] Further, 0.1-0.5 wt% of calcium amino triacetate complex is also added in the S2.2 step.

[0023] Further, 0.5-2.0 wt% of phosphate is also added in the S2.3 step, which is one or more of trisodium phosphate, sodium aluminum phosphate, or sodium pyrophosphate.

[0024] Further, the separation method of the residue in the filtrate generated by water washing in the S2 step is as follows: (1) the fly ash particles are separated by a screening device.

[0025] (2) the filtrate after the separation of the fly ash particles is separated into a sludge layer by sedimentation.

[0026] (3) the sludge layer is mechanically pressed, dried, and crushed to obtain the residue.

[0027] Further, the silicon-aluminum conditioning agent is a high-silicon glass powder with a SiO2 content higher than 80 wt% mixed with calcium aluminate with an Al2O3 content higher than 40 wt% at a Si / Al molar ratio of 2.5-4.0.

[0028] Further, the auxiliary components also include 0.5-3 wt% of sodium carbonate, 1-5 wt% of calcium hydroxide, and 1-3 wt% of boric acid glass powder, each accounting for 0.5-3 wt% of the total mass of all substances in the S4 step.

[0029] Further, a two-stage pressing method is used in the S5 step, first, the mixed material is pressed to form a preformed block at a first pressure of 5-10 MPa, and the pressure holding time is 3-5 minutes, and then a final pressing treatment is performed at a second pressure of 15-30 MPa, and the pressure holding time is 2-4 minutes.

[0030] In the S6 step, the pressing block is heated in a programmed heating manner: Stage I: from room temperature to 350℃ at a rate of 1-2℃ / min, and the holding time is 40-60 minutes.

[0031] Stage II: from 3-5℃ / min to 480-520℃, and the holding time is 30-45 minutes.

[0032] Stage III: from 5-8℃ / min to 600℃, and the holding time is 10-20 minutes.

[0033] Compared with the prior art, the beneficial effects of the present application mainly manifest in the following aspects: (1) The present process, by controlling the particle size after crushing and the three-stage pH water washing steps, combined with the use of organic acid, buffer system and alkaline additive, can desorb metal ions of different valence states respectively, which is conducive to reducing the content of residual heavy metals in fly ash after water washing, and provides a pretreatment basis for subsequent heat treatment.

[0034] (2) By setting the proportion of auxiliary components, including silicon-aluminum conditioning agent, foam glass microbeads, starch and polycarboxylic acid water reducer, etc., it is beneficial to enhance the forming fluidity and compaction density of the mixture, control the porosity range, and improve the mechanical structure uniformity of the pressed block.

[0035] (3) In the initial water washing stage, the pH gradient interval is divided and functional additives are introduced, so that a coating layer with reactivity is gradually formed on the surface of the particles. Among them, under the condition of acidic water washing, water-soluble silicon source is introduced, which helps to form a soluble silicate layer on the surface of the particles, improves the interface matching with the subsequent conditioning agent, and provides precursor units for the glass network structure.

[0036] The introduction of calcium amino triacetate complex in the neutral water washing stage can further capture soluble heavy metals and form Ca complex structure on the surface of the particles, providing active Ca source that can participate in glass structure construction for the subsequent mixture. The addition of phosphate mineralization additives in the alkaline water washing stage can introduce P elements to form components that can participate in sodium-calcium phosphate and Na-P-Si glass phase, improving the network structure integrity and thermal reactivity of the subsequent molten product.

[0037] In the component conditioning link, by introducing Si / Al complex conditioning agent composed of high-silicon glass powder and calcium aluminate, a glass precursor of Si-O-Al skeleton easy to form in heat treatment is constructed. Further adding sodium carbonate, calcium hydroxide and boric acid glass powder helps to enhance the functions of acid-base neutralization, fluxing and network bonding, among which sodium carbonate enhances reactivity, calcium hydroxide supplements alkaline adjustment, and boric acid glass powder promotes the formation of B-O-Si structure, improving the thermal stability and inertness of the final glass body.

[0038] The forming stage adopts a double-pressure pressing strategy, first realizing the initial arrangement and pre-bonding of particles through medium pressure, and then forming a structure complete briquette through high pressure compaction, which is conducive to improving the mechanical strength of sintering and melting precursor and controlling the gas channel.

[0039] Finally, in the melting stage, the Si-O-Al-Ca-P-B composite glass network precursor structure constructed by the above-mentioned links can form a solid waste vitrification product with a glass body content of more than 95%, and stably contain the original heavy metals and complex components in the fly ash, so as to realize the unified control of thermal stability, mechanical properties and leaching resistance. DETAILED DESCRIPTION

[0040] The application will be described in detail below with reference to examples.

[0041] Example 1: This embodiment discloses a chelated post-landfill fly ash reclamation disposal process, which specifically comprises the following steps: S1: crushing treatment: the chelated fly ash blocks after landfill are subjected to primary crushing using a double-shaft shearing crusher, and then subjected to further crushing by a hammer impact crusher, and the obtained fly ash particles have a particle size of 20 mm. To avoid interference of metal inclusions on the subsequent melting process, a magnetic iron removal link can be arranged at the front end of the crushing. Controlling the particle size in a small range helps to improve the contact efficiency of subsequent water washing and the uniformity of heat conduction during heat treatment.

[0042] S2: multi-stage water washing treatment: the crushed fly ash particles are subjected to multi-stage water washing treatment, which comprises the following stages: S2.1: first water washing: under the condition that the pH is adjusted to 6.0, the fly ash is subjected to the first round of water washing. The pH adjusting agent is citric acid, and the concentration is controlled at 0.2 mol / L to gently strip the chelated residual metals. To promote the formation of a preliminary skeleton structure on the surface of the fly ash particles, sodium metasilicate is added as a water-soluble silicon source additive, and the addition amount is 2 wt% of the mass of the fly ash. The reaction time is set to 60 minutes, the liquid-solid ratio is controlled at 10:1, the stirring speed is 300 rpm, and the system temperature is controlled at 40℃ to ensure the kinetic rate of the water washing reaction and control the energy consumption.

[0043] S2.2: second water washing: the water-washed fly ash is subjected to the second washing under the condition that the pH is adjusted to 7.5, and a phosphate buffer system (NaH2PO4 and Na2HPO4) is used to maintain a stable neutral environment. At the same time, 0.5 wt% of calcium amino triacetate complex (Ca-EDTA) is added, which has strong complexing ability for divalent and trivalent metals such as Fe, Cu and Zn, and can further stabilize the free heavy metal ions. The reaction time of this step is set to 40 minutes, the liquid-solid ratio is 8:1, the system stirring rate is kept uniform, and the temperature is controlled at 30℃.

[0044] S2.3: Third water washing: Continue to adjust the pH of fly ash, increase to 10.0, use sodium hydroxide, sodium carbonate and sodium bicarbonate three alkali sources combined adjustment. In order to further promote the stable solidification of metal ions, 2.0 wt% of phosphate is added in this stage, including trisodium phosphate, sodium pyrophosphate and sodium aluminum phosphate compound mixture. The reaction time is 30 minutes, the liquid-solid ratio is controlled at 7:1, the stirring rate is moderate, and the temperature is maintained at 35℃. This step can effectively form insoluble precipitates such as Pb3(PO4)2 and ZnNaPO4, significantly reducing the risk of heavy metal migration.

[0045] S3: Dewatering treatment: The fly ash after three-stage water washing is mechanically dewatered by vacuum belt filter system. After preliminary dewatering, the water content is controlled at about 30%. Then it is transferred to hot air drying system and dried at 80℃ hot air condition, so that the water content of fly ash is further reduced to 25%, providing good physical state for subsequent mixing and forming.

[0046] S4: Mixing raw material: 100 parts of mixed material composed of fly ash after S3 dewatering and fly ash with any ratio of fly ash after three-stage countercurrent water washing, and 15 parts of residue recovered from S2 water washing are mixed. The residue recovery step includes: first, separate larger fly ash particles by screening device; second, let the remaining filtrate stand to form sludge layer; finally, the sludge is dewatered by pressure filtration, dried at 60℃ low temperature and crushed to form usable powder residue.

[0047] Fly ash after three-stage countercurrent water washing of fly ash: fly ash collected in the waste incineration flue gas system, which is subjected to A1: first water washing at pH 5.5.

[0048] A2: Second water washing at pH 7.0.

[0049] A3: Third water washing at pH 9.0.

[0050] A4: Dewatering treatment, the water content is controlled at 20%.

[0051] The following auxiliary ingredients are added on the basis of the above: 25 parts of silicon aluminum conditioner (mixed with high-silicon glass powder and calcium aluminate, SiO2 content is higher than 70 wt%, Al2O3 content is higher than 40 wt%, Si / Al molar ratio is 4.0), 3 parts of foam glass beads for improving the density and thermal insulation performance of the pressed body, 3 parts of starch for providing thermal decomposition into pores, and 0.5 parts of polycarboxylic acid water reducer for improving fluidity and uniform dispersion.

[0052] In addition, to optimize the mineralization reaction conditions, 3 wt% of sodium carbonate, 5 wt% of calcium hydroxide, and 3 wt% of boric acid glass powder were added to the total mass of the fly ash mixture to enhance the alkaline reaction environment and improve the subsequent glass phase generation ability and melting reaction efficiency.

[0053] The mixing process was carried out using a twin-shaft ribbon mixer at a speed of 80 rpm for 10 min to ensure that all components were evenly dispersed without obvious agglomeration or segregation.

[0054] S5: Cold Pressing: The uniformly mixed materials are fed into a press machine for a two-stage press forming process. The first stage involves pre-pressing at 10 MPa, held for 5 minutes, to expel air and pre-form the structure. The second stage involves final pressing at 30 MPa, held for 4 minutes, to achieve a compact with a porosity of less than 25%. This results in a dense structure with a smooth, crack-free surface, making it suitable for subsequent heat treatment.

[0055] S6: Programmed temperature heat treatment: The pressed block enters the electric heating furnace for staged programmed temperature heat treatment: In the first stage, the temperature is increased from room temperature to 350°C at 2°C / min and kept at this temperature for 60 minutes to remove residual moisture in the material and thermally decompose starch.

[0056] In the second stage, the temperature was continued to rise to 520°C at a rate of 5°C / min and kept at that temperature for 45 minutes to promote the structural rearrangement of the internal reaction system.

[0057] In the third stage, the temperature is raised to 600°C at 8°C / min and kept at this temperature for 20 minutes to form a stable pre-formed structure.

[0058] This heat treatment process can effectively release internal stress and form a block with good thermal stability, providing a structural basis for the high-temperature melting stage.

[0059] S7: High-temperature melting: The preformed block is placed in a melting furnace and melted at 1350°C for 30 minutes, either using a plasma or induction furnace. During the melting process, the heavy metals are fixed in the glassy structure or mineral crystals, rendering them bioactive and non-mobile. After melting, the block is cooled, resulting in a dense and uniform glassy or mineral structure.

[0060] Example 2: This example discloses a process for recycling fly ash after chelation landfill, specifically comprising the following steps: S1: Crushing: The chelated fly ash blocks after landfill are initially crushed using a dual-shaft shear crusher and further crushed using a hammer impact crusher. The resulting fly ash particles are controlled to a particle size of 5 mm. To prevent metal inclusions from interfering with the subsequent melting process, a magnetic iron removal process can be installed at the crushing front. Keeping the particle size within a small range helps improve contact efficiency during subsequent water washing and uniform heat conduction during heat treatment.

[0061] S2: Multi-stage water washing treatment: The broken fly ash particles are subjected to multi-stage water washing treatment, which includes the following stages: S2.1: First water washing: The fly ash is subjected to the first round of water washing under the condition that the pH is adjusted to 5.5. The pH adjuster is citric acid, and the concentration is controlled at 0.2 mol / L to strip the chelated residual metals under mild conditions. In order to promote the formation of a preliminary skeleton structure on the surface of the fly ash particles, sodium metasilicate is added as a water-soluble silicon source additive, and the addition amount is 0.5 wt% of the mass of the fly ash. The reaction time is set to 60 minutes, the liquid-solid ratio is controlled at 10:1, the stirring speed is 300 rpm, and the system temperature is controlled at 40°C to ensure the kinetic rate of the water washing reaction and control the energy consumption.

[0062] S2.2: Second water washing: The water-washed fly ash is subjected to the second washing under the condition that the pH is adjusted to 7.0, and a phosphate buffer system (NaH2PO4 and Na2HPO4) is used to maintain a stable neutral environment. At the same time, 0.1 wt% of calcium amino triacetate complex (Ca-EDTA) is added, which has strong complexing ability for Fe, Cu, Zn and other divalent and trivalent metals, and can further stabilize free heavy metal ions. The reaction time of this step is set to 40 minutes, the liquid-solid ratio is 8:1, the system stirring speed is kept uniform, and the temperature is controlled at 30°C.

[0063] S2.3: Third water washing: The fly ash is continuously subjected to pH adjustment, and the pH is increased to 9.0, and sodium hydroxide, sodium carbonate and sodium bicarbonate are used to jointly adjust. In order to further promote the stable solidification of metal ions, a total of 0.5 wt% of phosphate is added at this stage, including a compound mixture of trisodium phosphate, sodium pyrophosphate and sodium aluminum phosphate. The reaction time is 30 minutes, the liquid-solid ratio is controlled at 7:1, the stirring speed is moderate, and the temperature is maintained at 35°C. This step can effectively form insoluble precipitates such as Pb3(PO4)2 and ZnNaPO4, significantly reducing the risk of heavy metal migration.

[0064] S3: Dewatering treatment: The fly ash after three-stage water washing is subjected to mechanical dewatering by a vacuum belt filter system, and the water content is controlled at about 30% after preliminary dewatering. Subsequently, it is transferred to a hot air drying system, and dried at 80°C hot air to further reduce the water content of the fly ash to 15%, providing a good physical state for subsequent mixing and forming.

[0065] S4: Mixing of raw materials: 100 parts of the mixture of the fly ash after S3 dewatering and the fly ash subjected to three-stage countercurrent water washing in any ratio, and 5 parts of the residue recovered from the water washing in S2 step, are thoroughly mixed. The recovery step of the residue includes: first, separating larger fly ash particles through a screening device; second, allowing the remaining filtrate to settle to form a sludge layer; and finally, the sludge is dewatered by pressure filtration, dried at 60°C, and then crushed to form a usable powder residue.

[0066] Fly ash raw fly ash: fly ash collected from waste incineration flue gas system, which is subjected to A1: first water washing of fly ash under the condition of pH 5.5.

[0067] A2: second water washing of fly ash under the condition of pH 7.0.

[0068] A3: third water washing of fly ash under the condition of pH 9.0.

[0069] A4: dewatering treatment, so that the water content is controlled at 20%.

[0070] The following auxiliary ingredients are added on the basis of the above: 10 parts of silicon aluminum conditioner (mixed from high-silicon glass powder and calcium aluminate, SiO2 content is higher than 70 wt%, Al2O3 content is higher than 40 wt%, Si / Al molar ratio is 2.5), 1 part of foam glass beads for improving the density and thermal insulation performance of the pressed body, 1 part of starch for providing pore-forming effect by thermal decomposition, 0.2 part of polycarboxylic acid water reducer for improving fluidity and uniform dispersion.

[0071] In addition, in order to optimize the mineralization reaction conditions, 0.5 wt% of sodium carbonate, 1 wt% of calcium hydroxide and 1 wt% of boric acid glass powder are also added to the total mass of fly ash mixture to enhance the alkaline reaction environment, improve the subsequent glass phase generation ability and melting reaction efficiency.

[0072] The mixing process adopts a double-shaft spiral belt stirrer, and the stirring is carried out at a speed of 80 rpm for 10 minutes to ensure that all components are uniformly dispersed without obvious aggregation or segregation.

[0073] S5: cold pressing: the uniformly mixed material is sent into a pressing equipment for two-stage pressing forming. In the first stage, pre-pressing is carried out at a pressure of 5 MPa, and pressure maintaining is carried out for 3 minutes to exclude air and pre-form the shape structure; in the second stage, final pressing treatment is carried out at a pressure of 15 MPa, and pressure maintaining is carried out for 2 minutes to obtain a formed block with a porosity controlled at 10%. The structure is dense, the surface is flat, and there is no crack, which is suitable for subsequent heat treatment.

[0074] S6: programmed temperature heat treatment: the pressed block is put into an electric furnace for staged programmed temperature heat treatment: in the first stage, the temperature is raised from room temperature to 350℃ at a rate of 1℃ / min, and the temperature is maintained for 40 minutes to remove residual moisture and heat-decomposed starch in the material.

[0075] In the second stage, the temperature is continued to be raised at a rate of 3℃ / min to 480℃, and the temperature is maintained for 30 minutes to promote the structural rearrangement of the internal reaction system.

[0076] In the third stage, the temperature is raised at a rate of 5℃ / min to 600℃, and the temperature is maintained for 10 minutes to form a stable pre-ceramic structure.

[0077] The heat treatment process can effectively release internal stress and form a bulk body with good thermal stability, providing a structural basis for the high-temperature melting stage.

[0078] S7: High-temperature melting treatment: The preformed bulk body is placed in a melting furnace and melted at 1200°C for 30 minutes, which can be achieved using a plasma melting furnace or an induction furnace. During the melting process, heavy metals are fixed in the glass phase structure or mineral crystals, and no longer have biological activity or migration. After melting and cooling, a dense and uniform glass or mineral structure product is obtained.

[0079] Example 3: This embodiment discloses a chelated post-landfill fly ash reclamation process, which specifically includes the following steps: S1: crushing treatment: the post-landfill chelated fly ash bulk body is initially crushed using a double-shaft shearing crusher, and then further crushed using a hammer impact crusher, and the obtained fly ash particles are controlled to have a particle size of 12.5 mm. To avoid interference of metal inclusions on the subsequent melting process, a magnetic iron removal step can be set at the front end of the crushing. Controlling the particle size within a small range helps to improve the contact efficiency of subsequent water washing and the uniformity of heat conduction during heat treatment.

[0080] S2: Multi-stage water washing treatment: The crushed fly ash particles are subjected to multi-stage water washing treatment, which includes the following stages: S2.1: First water washing: under the condition that the pH is adjusted to 5.75, the fly ash is subjected to the first round of water washing. The pH adjuster is citric acid, and the concentration is controlled at 0.2 mol / L to gently strip the chelated residual metals. To promote the formation of a preliminary skeletal structure on the surface of the fly ash particles, sodium metasilicate is added as a water-soluble silicon source additive, and the addition amount is 1.25 wt% of the mass of the fly ash. The reaction time is set to 60 minutes, the liquid-solid ratio is controlled to 10:1, the stirring speed is 300 rpm, and the system temperature is controlled to 40°C to ensure the kinetic rate of the water washing reaction and control the energy consumption.

[0081] S2.2: Second water washing: the water-washed fly ash is subjected to the second washing under the condition that the pH is adjusted to 7.25, and a phosphate buffer system (NaH2PO4 and Na2HPO4) is used to maintain a stable neutral environment. At the same time, 0.3 wt% of calcium amino triacetate complex (Ca-EDTA) is added, which has strong complexing ability for divalent and trivalent metals such as Fe, Cu, and Zn, and can further stabilize free heavy metal ions. The reaction time of this step is set to 40 minutes, the liquid-solid ratio is 8:1, the system stirring rate is kept uniform, and the temperature is controlled to 30°C.

[0082] S2.3: Third water washing: Continue to adjust the pH of fly ash, increase to 9.5, use sodium hydroxide, sodium carbonate and sodium bicarbonate three alkali source combined adjustment. In order to further promote the stable solidification of metal ions, 1.25 wt% of phosphate is added in this stage, including trisodium phosphate, sodium pyrophosphate and sodium aluminum phosphate compound mixture. The reaction time is 30 minutes, the liquid-solid ratio is controlled at 7:1, the stirring rate is moderate, and the temperature is maintained at 35°C. This step can effectively form insoluble precipitates such as Pb3(PO4)2 and ZnNaPO4, significantly reducing the risk of heavy metal migration.

[0083] S3: Dewatering treatment: The fly ash after three-stage water washing is mechanically dewatered by vacuum belt filter system. After preliminary dewatering, the water content is controlled at about 30%. Then it is transferred to hot air drying system, dried at 80°C hot air condition, and the water content of fly ash is further reduced to 20%, providing good physical state for subsequent mixing and forming.

[0084] S4: Mixing material: 100 parts of the mixture of S3 dewatered fly ash and fly ash raw ash with any ratio of fly ash after three-stage countercurrent water washing are mixed with 10 parts of residue recovered from S2 water washing. The residue recovery step includes: first, separate larger fly ash particles by screening device; second, let the remaining filtrate stand to form a sludge layer; finally, the sludge is dewatered by pressure filtration, dried at 60°C, and crushed to form a usable powder residue.

[0085] Fly ash raw ash after three-stage countercurrent water washing: fly ash collected in the waste incineration flue gas system, after A1: first water washing of fly ash at pH 5.5.

[0086] A2: Second water washing of fly ash at pH 7.0.

[0087] A3: Third water washing of fly ash at pH 9.0.

[0088] A4: Dewatering treatment, the water content is controlled at 20%.

[0089] On the basis of the above, the following auxiliary ingredients are added: 17.5 parts of silicon aluminum conditioner (mixed with high-silicon glass powder and calcium aluminate, SiO2 content higher than 70 wt%, Al2O3 content higher than 40 wt%, Si / Al molar ratio 3.25), 2 parts of foam glass beads for improving the density and thermal insulation performance of the pressed body, 2 parts of starch for providing thermal decomposition into pores, 0.35 parts of polycarboxylic acid water reducer for improving fluidity and uniform dispersion.

[0090] In addition, to optimize the mineralization reaction conditions, 1.75 wt% sodium carbonate, 3 wt% calcium hydroxide and 2 wt% boric acid glass powder were added to the total mass of the fly ash mixture to enhance the alkaline reaction environment and improve the subsequent glass phase generation ability and melting reaction efficiency.

[0091] The mixing process used a double-shaft spiral ribbon mixer, which was stirred at a speed of 80 rpm for 10 minutes to ensure that all components were uniformly dispersed without obvious agglomeration or segregation.

[0092] S5: Cold pressing: The uniformly mixed material was fed into a pressing device for two-stage pressing. In the first stage, the material was pre-pressed at a pressure of 7.5 MPa for 4 minutes to remove air and pre-form the shape structure. In the second stage, the material was finally pressed at a pressure of 22.5 MPa for 3 minutes to obtain a shaped body with a porosity controlled within 17.5%. The structure was dense, the surface was flat, and there were no cracks, which was suitable for subsequent heat treatment.

[0093] S6: Programmed temperature heat treatment: The pressed body was placed in an electric furnace for staged programmed temperature heat treatment. In the first stage, the temperature was raised from room temperature to 350°C at a rate of 1.5°C / min and held for 50 minutes to remove residual moisture and thermally decompose the starch in the material.

[0094] In the second stage, the temperature was continued to be raised to 500°C at a rate of 4°C / min and held for 37.5 minutes to promote the structural rearrangement of the internal reaction system.

[0095] In the third stage, the temperature was raised to 600°C at a rate of 6.5°C / min and held for 15 minutes to form a stable pre-ceramic structure.

[0096] This heat treatment process can effectively release internal stress and form a body with good thermal stability, providing a structural basis for the high-temperature melting stage.

[0097] S7: High-temperature melting treatment: The pre-ceramic body was placed in a melting furnace and melted at 1275°C for 30 minutes using a plasma melting furnace or an induction furnace. During the melting process, heavy metals were fixed in the glass phase structure or mineral crystals and no longer had biological activity or migratory properties. After melting, the product was cooled to obtain a dense and uniform glass or mineral structure.

[0098] Example 4 differs from Example 3 in that no water-soluble silicon source additive was added in step S2.1.

[0099] Example 5 differs from Example 3 in that no calcium amino triacetate complex was added in step S2.2.

[0100] Example 6 differs from Example 3 in that no phosphate was added in step S2.3.

[0101] Example 7 differs from Example 3 in that the silicon-aluminum conditioner is a high-silica glass powder with a SiO2 content higher than 80 wt% mixed with calcium aluminate with an Al2O3 content higher than 40 wt% at a Si / Al molar ratio of 5.

[0102] Example 8 differs from Example 3 in that the silicon-aluminum conditioner is a high-silica glass powder with a SiO2 content higher than 80 wt% mixed with calcium aluminate with an Al2O3 content higher than 40 wt% at a Si / Al molar ratio of 1.

[0103] Example 9 differs from Example 3 in that the silicon-aluminum conditioner is a silicon-containing glass powder with a SiO2 content of 50-60 wt% mixed with calcium aluminate with an Al2O3 content of 20-30 wt% at a Si / Al molar ratio of 3.25.

[0104] Example 10 differs from Example 3 in that the silicon-aluminum conditioner is calcium aluminate with an Al2O3 content higher than 40 wt%.

[0105] Example 11 differs from Example 3 in that sodium carbonate, calcium hydroxide, and boric acid glass powder are not added in the auxiliary component.

[0106] Example 12 differs from Example 3 in that the S5 and S6 steps are different.

[0107] S5: Cold pressing: The uniformly mixed fly ash base material is loaded into a metal mold, and a one-time pressing method at room temperature is used for cold pressing. The pressing pressure applied is 20 MPa, and the duration is 3 minutes to ensure that the material inside is fully compacted and that stable connections are formed between the particles.

[0108] S6: Heat treatment: The pressed block is placed in a box-type resistance furnace and subjected to heat treatment in an air atmosphere. The heating temperature is set to 500°C, the heating rate is 5°C / min, and the temperature is maintained for 40 minutes after reaching the set value to ensure uniform heating and sufficient reaction inside and outside the block.

[0109] Comparative Example 1: S1: Crushing treatment: The landfill chelated fly ash is preliminarily crushed using a double-shaft shearing crusher, and then further refined using a hammer impact crusher, with the particle size of the crushed fly ash controlled to be 20 mm. The obtained particles are irregular in shape, and some landfill deposition residues are attached to the surface.

[0110] S2: Ordinary water washing treatment: The crushed fly ash is added to water for conventional stirring and washing, with the liquid-solid ratio set to 5:1, the stirring time at room temperature set to 30 minutes, and no pH adjustment or staged washing performed. After washing, the solid-liquid separation is performed, the filtrate is directly discarded, and no recovery treatment, stabilizing aid, or silicon source control material is added.

[0111] S3: Dehydration treatment: After water washing, the fly ash is preliminarily dehydrated by a vacuum filtration device, and then dried in a hot air dryer at 80°C to control the water content at 20%, obtaining a semi-dry powder material that can flow freely.

[0112] S4: Mixing of raw materials: The dehydrated fly ash is mixed with the following auxiliary components to obtain a mixture: silicon-aluminum conditioner: 15 parts are added, containing a mixture of SiO2 and Al2O3, without precise control of the molar ratio; foam glass beads: 2 parts are added; starch: 2 parts are added; polycarboxylic acid water reducer: 0.3 parts are added.

[0113] No water-washed residue, no addition of sodium carbonate, calcium hydroxide or boric acid glass, etc. Stable fluxing materials. The mixing operation is completed in a double-shaft blade mixer, and stirring is carried out at room temperature for 5 minutes.

[0114] S5: Cold pressing: The mixture is loaded into a mold for primary pressing, with a pressure of 20 MPa, and the mold is released after 3 minutes of pressure retention, obtaining a pressed block. The obtained pressed block has a porosity of about 20% and has a certain structural stability, but the compaction degree is lower than the optimized scheme.

[0115] S6: Heat treatment: The pressed block is placed in an electric heating furnace and heat treated at 500°C for 40 minutes. This process mainly realizes the preliminary decomposition of organic components and structural fixation. There is no programmed temperature rise section and no stepwise temperature control.

[0116] S7: High-temperature melting treatment: The heat-treated block is placed in a high-temperature furnace and subjected to melting treatment at 1300°C for 30 minutes, and then cooled to obtain a solid product. The obtained product has a dense appearance, but the glass phase is not fully developed, with uneven crystals and residual pores, etc. Subsequent tests show that its heavy metal leaching performance still has certain risks.

[0117] Test method: 1. According to the provisions of HJ 557-2010 / GB T 5750.6-2023 (water leaching), the leaching amounts of Cu, Zn, Cd, Pb, Ni and Cr(VI) are detected.

[0118] 2. According to GB / T 5072-2008 "Inorganic Non-metallic Materials - Test Method for Compressive Strength", the mechanical integrity is measured.

[0119] 3. According to GBT41015-2021 Solid Waste Glassification Product Technical Requirements, the glass content is measured.

[0120] The above test results are shown in Tables 1 and 2.

[0121] Table 1 Test results:

[0122] Table 2: Results of leaching amount detection

[0123] The above merely describes the preferred embodiments of the present application, and the protection scope of the present application is not limited to the above-mentioned embodiments. Any technical scheme falling within the concept of the present application shall fall within the protection scope of the present application. It should be noted that, for ordinary skilled persons in the art, some improvements and refinements without departing from the principles of the present application shall also be considered as the protection scope of the present application.

Claims

1. A process for recycling fly ash after chelation landfill, characterized in that: The following steps are involved: S1: After the chelated fly ash is excavated from the landfill, it is crushed to control the particle size of the fly ash particles obtained after crushing to be within the range of 5 to 20 mm; S2: The crushed fly ash particles are subjected to a multi-stage water washing process in sequence, wherein the multi-stage water washing process includes the following stages: S2.1: The fly ash is subjected to a first water washing at a pH of 5.5 to 6.0; S2.2: The fly ash is subjected to a second water washing at a pH of 7.0 to 7.5; S2.3: The fly ash is subjected to a third water washing at a pH of 9.0 to 10.0; S3: Dehydrating the washed fly ash to control its moisture content within the range of 15% to 25%; S4: Mixing the dehydrated fly ash, the residue in the filtrate produced by the washing in step S2, and auxiliary components to prepare a mixture; the auxiliary components include a silicon-aluminum conditioner, foam glass microspheres, starch, and a polycarboxylic acid water reducer; S5: Cold-pressing the mixture to obtain a pressed block with a porosity of 10% to 25%; S6: Heat-treating the pressed block at 400 to 600°C to obtain a pre-formed block; S7: Melting the pre-formed block at 1200 to 1350°C, and then quenching it with water to obtain a stable glass and / or mineral structure product.

2. The fly ash recycling process after chelating landfill according to claim 1 is characterized in that: In step S4, the weight proportions of the various components are as follows: 100 parts of a mixture of fly ash dehydrated from S3 and fly ash obtained by three-stage countercurrent washing in any ratio, 5-15 parts of the residue in the filtrate produced by the water washing in step S2, 10-25 parts of a silicon-aluminum conditioning agent, 1-3 parts of foam glass microspheres, 1-3 parts of starch, and 0.2-0.5 parts of a polycarboxylate water reducer; the fly ash obtained by three-stage countercurrent washing is fly ash collected from a waste incineration flue gas system, and the fly ash is subjected to a first water washing at a pH of 5.5-6.0 in step A1; A2: Wash the fly ash for the second time at a pH of 7.0-7.5; A3: Wash the fly ash for the third time at a pH of 9.0-10.

0. A4: Dehydration treatment to control the moisture content to 20% to 25%.

3. The fly ash recycling process after chelating landfill according to claim 1 is characterized in that: In step S2.1, an organic acid is used to adjust the pH; In step S2.2, an acid-base buffer system is used to adjust the pH; In step S2.3, one or more of sodium hydroxide, sodium carbonate or sodium bicarbonate is used to adjust the pH.

4. The fly ash recycling process after chelating landfill according to claim 3 is characterized in that: In step S2.1, a water-soluble silicon source additive is also added. The water-soluble silicon source additive is sodium silicate or sodium metasilicate, and its addition amount is controlled to be 0.5 to 2 wt% of the mass of the water-washed fly ash.

5. The fly ash recycling process after chelating landfill according to claim 3 is characterized in that: In step S2.2, 0.1 to 0.5 wt% of a calcium aminotriacetate complex is also added.

6. The fly ash recycling process after chelating landfill according to claim 3 is characterized in that: In step S2.3, 0.5 to 2.0 wt% of phosphate is further added, wherein the phosphate is one or more of trisodium phosphate, sodium aluminum phosphate or sodium pyrophosphate.

7. The fly ash recycling process after chelating landfill according to claim 1 is characterized in that: The method for separating the residue in the filtrate produced by water washing in step S2 is as follows: (1) separating the fly ash particles through a filtering device; (2) separating the sludge layer from the filtrate after the fly ash particles are separated by sedimentation; and (3) mechanically filtering, drying, and crushing the sludge layer to obtain the residue.

8. The process for recycling fly ash after chelating landfill according to claim 1 is characterized in that: The silicon-aluminum conditioning agent is obtained by mixing high-silicon glass powder with a SiO2 content higher than 80 wt% and calcium aluminate with an Al2O3 content higher than 40 wt% at a Si / Al molar ratio of 2.5 to 4.

0.

9. The process for recycling fly ash after chelating landfill according to claim 8, characterized in that: The auxiliary components also include 0.5-3 wt% of sodium carbonate, 1-5 wt% of calcium hydroxide, and 1-3 wt% of boric acid glass powder, respectively, based on the total mass of all substances in step S4.

10. The fly ash recycling process after chelating landfill according to claim 1 is characterized in that: In step S5, a two-stage pressing method is adopted. First, the mixture is pressed to form a preformed block at a first pressure of 5 to 10 MPa, and the pressure holding time is 3 to 5 minutes. Then, a final pressing treatment is performed at a second pressure of 15 to 30 MPa, and the pressure holding time is continued for 2 to 4 minutes. In step S6, the pressed block adopts a programmed temperature rising method during the S6 heat treatment process: stage I: from room temperature to 350°C at 1 to 2°C / min, and keep warm for 40 to 60 minutes; stage II: from 480 to 520°C at 3 to 5°C / min, and keep warm for 30 to 45 minutes; stage III: from 600°C to 600°C at 5 to 8°C / min, and keep warm for 10 to 20 minutes.

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