Foaming culture stone with high mixing amount of municipal sludge and preparation method of foaming culture stone

Abstract

The invention belongs to the technical field of sludge recycling, and discloses a high-content municipal sludge foaming culture stone and a preparation method thereof.The foaming culture stone is prepared from a first component and a second component, the first component is prepared from, by mass, 85-93% of municipal sludge, 3-13% of shield mud and 2-5% of talc, and the second component is prepared from, by mass, 20-30% of the municipal sludge, 3-13% of the shield mud and 2-5% of the talc; the second component comprises a foaming agent, and the mass of the second component accounts for 0.05-0.50% of the total mass of the first component. The problem that municipal sludge is difficult to treat is efficiently solved, and reutilization of multi-mixing-amount solid waste resources is achieved.

Description

Technical Field

[0001] This invention belongs to the field of sludge recycling technology, specifically relating to a foamed cultured stone with high content of municipal sludge and its preparation method. Background Technology

[0002] Municipal sludge generally refers to sludge collected from municipal pipelines, which, after drying at wastewater treatment plants, has a moisture content of 50-60%. Resource utilization of municipal sludge is one approach to its treatment. For example, municipal sludge can be used in the ceramics industry as a raw material for ceramic production. For instance, patent publication number CN110407556A discloses a method for preparing lightweight, high-strength foamed ceramic bricks using municipal sludge and its application, requiring sludge pretreatment and a maximum sludge content of 78%. Patent publication number CN112279677A discloses foamed ceramics with high municipal sludge content and its preparation method, where the municipal sludge content can reach 80%, requiring the addition of clay, potassium feldspar, and other raw materials to supplement the required elements. However, the most significant characteristics of municipal sludge are: 1. High organic matter content, resulting in high loss on ignition; 2. High iron content, causing it to turn black after firing; 3. Containing calcium, sulfur, and phosphorus, resulting in high loss on ignition. Therefore, municipal sludge is difficult to apply in large quantities in the field of building ceramics with high whiteness requirements and foamed ceramics with uniform foaming requirements. Moreover, the application of municipal sludge in ceramic products requires the addition of other raw materials to make up for the lack of elements, and its upper limit of dosage is difficult to increase further.

[0003] Therefore, it is necessary to propose new solutions for the recycling and utilization of municipal sewage sludge. Summary of the Invention

[0004] To address the aforementioned technical problems, the present invention aims to provide a foamed cultured stone with high content of municipal sludge and its preparation method, which effectively solves the problem of difficult municipal sludge treatment and realizes the reuse of solid waste resources with high content.

[0005] To achieve the above-mentioned objectives, the technical solution adopted by the present invention is as follows: In a first aspect, the present invention proposes a foamed cultured stone with a high content of municipal sludge. The raw materials for preparing the foamed cultured stone include a first component and a second component. Based on the mass of the first component, the first component includes 85-93% municipal sludge, 3-13% shield tunneling mud, and 2-5% talc. The second component includes a foaming agent, and the mass of the second component accounts for 0.05-0.50% of the total mass of the first component.

[0006] Preferably, municipal sludge refers to sludge collected from municipal pipelines with a water content of 50-60%.

[0007] More preferably, based on municipal sludge, the elemental composition of municipal sludge, calculated by mass percentage, includes: 5-20% Al2O3, 10-30% SiO2, 1-5% K2O, 1-6% CaO, and 3-10% Fe2O3.

[0008] Preferably, the tunnel boring machine (TBM) mud includes one or both of virgin mud and mixed mud. Virgin mud refers to solid waste mud excavated during construction without the addition of lime, while mixed mud refers to a mixture of virgin mud and lime.

[0009] More preferably, based on virgin mud, the elemental composition of virgin mud, calculated by mass percentage, includes: 10-15% Al2O3, 70-75% SiO2, 1-3% K2O, 0-2% CaO and 2-5% Fe2O3.

[0010] More preferably, based on the mixed mud, the elemental composition of the mixed mud, calculated by mass percentage, includes: 12-15% Al2O3, 65-75% SiO2, 1-5% K2O, 1-3% CaO and 2-5% Fe2O3.

[0011] Preferably, in talc, the mass percentage of silicon dioxide is ≥60% and the mass percentage of magnesium oxide is ≥30%.

[0012] Preferably, the foaming agent is silicon carbide powder, with a SiC mass percentage ≥ 99%.

[0013] In a second aspect, the present invention provides a method for preparing foamed cultured stone with a high content of municipal sludge, comprising: S1. Pretreatment: The raw materials include municipal sludge, shield tunnel mud, talc and foaming agent. The raw materials are dried, ground and sieved separately, and the sieved material is collected for later use. S2. Dry pressing: Mix the sieved material according to the formula ratio, add water and mix, then dry press to obtain the green body; S3. Firing: The blank is fired to obtain foamed cultural stone products.

[0014] Preferably, in step S3, the firing profile is as follows: heating from room temperature to 500~650℃ for 20~40 min; heating from 500~650℃ to 850~950℃ for 20~40 min, then holding for 40~80 min; heating from 850~950℃ to 1050~1100℃ for 20~60 min, then holding for 70~150 min; heating from 1050~1100℃ to 1150~1170℃ for 20~40 min, then holding for 20~40 min at 1150~1170℃.

[0015] Beneficial effects: This invention designs a firing curve for foamed cultured stone, ensuring that the finished product does not crack or deform even with a high amount of municipal sludge: During the firing process, the green body is rapidly heated to 850~950℃ and then transitions to the medium-temperature zone. The heating time from 850~950℃ to 1050~1100℃ and the holding time are extended, which is conducive to the full oxidation and decomposition of each component, making the internal and surface temperatures of the green body uniform. This avoids local low-melting-point melting and collapse caused by phosphorus, sulfur and other components in municipal sludge, allowing the glass phase to be fully generated and fill the interparticle gaps, reducing porosity and increasing density and mechanical strength. Addressing the issue of high organic content in municipal sludge, if there is insufficient venting time, the organic matter will concentrate and vaporize, damaging the green body structure and causing cracking and deformation of the cultured stone product. The extension of the medium-temperature zone allows for slow venting and phased liquid-phase processing, effectively solving the problems of cracking and deformation.

[0016] This invention proposes a unique raw material formula for high-volume municipal sludge, adding raw materials with low loss on ignition and high silicon and aluminum content, namely shield tunneling mud. In the system, the silicon component can build a glass network skeleton to improve product strength, the aluminum component can improve chemical stability and mechanical strength, and the raw material with low loss on ignition can reduce the cracking problem of cultured stone during the production process.

[0017] The foamed cultured stone prepared by this invention has a municipal sludge content as high as 85-93%, and the finished foamed cultured stone does not crack or deform, effectively solving the problem of "difficult treatment" of municipal sludge and realizing the reuse of solid waste resources with high admixture content. Detailed Implementation

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, specific implementation methods of the present invention will be described below. Obviously, those skilled in the art can obtain other implementation methods based on the embodiments described below without any creative effort.

[0019] This invention utilizes municipal sludge in the manufacture of artificial cultured stone. Specifically, this invention proposes a foamed cultured stone with a high content of municipal sludge. The raw materials for preparing the foamed cultured stone include a first component and a second component. Based on the mass of the first component, the first component comprises 85-93% municipal sludge, 3-13% tunnel boring machine mud, and 2-5% talc. The second component includes a foaming agent, and the mass of the second component accounts for 0.05-0.50% of the total mass of the first component.

[0020] Cultured stone combines natural texture with artistic expression, and is widely used in interior and exterior walls and landscape design. Currently, even when using municipal sludge as a raw material, conventional foamed ceramic products on the market cannot achieve a sludge content of 85%. This invention uses municipal sludge to prepare cultured stone, greatly increasing the amount of municipal sludge incorporated. In addition, the black color of municipal sludge after firing also meets the simulation requirements of artificial cultured stone.

[0021] Municipal sludge refers to sludge collected from municipal pipelines, which is dried at a sewage treatment plant and has a moisture content of 50-60%. In this invention, municipal sludge and tunnel boring machine mud are used as the main raw materials, that is, the main components of the raw materials are sludge or waste. The amount of municipal sludge is as high as 85-93% (the content of the second component is relatively low, and the amount of municipal sludge in the first component can be approximately regarded as the amount of municipal sludge in the overall raw materials), thus realizing the recycling of waste.

[0022] Furthermore, based on municipal sewage sludge, the elemental composition of municipal sewage sludge, calculated by mass percentage, includes: 5-20% Al₂O₃, 10-30% SiO₂, 1-5% K₂O, 1-6% CaO, and 3-10% Fe₂O₃. The remaining elements are present in very small amounts and are not critical elements, so they are not required. In this field, the elemental composition testing of municipal sewage sludge is generally performed after drying, and the same applies below.

[0023] Shield tunneling mud refers to natural, inorganic, low-value, low-quality solid waste mud excavated during the construction of tunnels, culverts, and real estate infrastructure. Shield tunneling mud has a moderate aluminum content and a high silicon content, which can solve the problem of insufficient silicon and aluminum elements in municipal sewage sludge. In addition, shield tunneling mud also contains potassium, which can supplement the potassium element in the formula and broaden the range of calcination processes.

[0024] Furthermore, based on shield tunneling mud, the elemental composition of shield tunneling mud, calculated by mass percentage, includes: 10-15% Al2O3, 65-75% SiO2, 1-5% K2O, 0-3% CaO, and 2-5% Fe2O3. The remaining elements are present in very small amounts and are not critical elements, so they are not required.

[0025] Furthermore, tunnel boring machine (TBM) slurry includes one or both of virgin slurry and mixed slurry. Virgin slurry refers to the solid waste slurry excavated during construction without the addition of lime, while mixed slurry is a mixture of virgin slurry and lime. The difference between virgin slurry and mixed slurry lies in whether lime is added; mixed slurry has a higher calcium content. Adding lime helps prevent bacterial growth. It's easy to understand that the choice between virgin slurry and mixed slurry is based on the raw material formula.

[0026] Furthermore, based on virgin mud, the elemental composition of virgin mud, calculated by mass percentage, includes: 10-15% Al2O3, 70-75% SiO2, 1-3% K2O, 0-2% CaO, and 2-5% Fe2O3. The remaining elements are present in very small amounts and are not critical elements, so they are not required.

[0027] Furthermore, based on the mixed mud, the elemental composition of the mixed mud, calculated by mass percentage, includes: 12-15% Al2O3, 65-75% SiO2, 1-5% K2O, 1-3% CaO, and 2-5% Fe2O3. The remaining elements are present in very small amounts and are not critical elements, so they are not required.

[0028] The talc used is commercially available talc powder. Preferably, the talc contains ≥60% silica and ≥30% magnesium oxide by mass. The magnesium in the talc powder forms a low-temperature eutectic with silicon and alkali metal oxides in municipal sludge and tunnel boring machine sludge, acting as a flux. At high temperatures, it generates a liquid phase that fills the pores of the green body, promoting densification. The lamellar structure of talc also helps regulate the shrinkage and deformation of the green body.

[0029] In this invention, the second component is similar to an additive, and the appropriate additive material is selected according to the product requirements. It is easy to understand that, in addition to the foaming agent, the second component may also contain other raw materials, such as one or more of the following: a green body reinforcing agent, a water-reducing agent, and a water-repellent agent. In this invention, the foaming agent is an important component; the formulation of the first component combined with the foaming agent can prepare a product with a foaming agent concentration of 1.0~1.5 g / cm³. 3 The foamed cultured stone, in addition to the foaming agent, may include one or more of a body strengthening agent, a water-reducing agent, and a water-repellent agent. The body strengthening agent improves the strength, wear resistance, and crack resistance of the body, reducing breakage after molding. The water-reducing agent reduces the water content of the body, improving fluidity. The water-repellent agent reduces the hydrophilicity of the body surface, improving the gloss and stain resistance of the glaze. The second component may also include other applicable additives in the art. It is readily understood that the amount of other additives in the second component, except for the foaming agent, can be zero. In the following specific embodiments, experiments are conducted using a foaming agent as the second additive; this is only to help understand the core idea of ​​the invention and should not limit the types of additives in the second component.

[0030] In this invention, the foaming agent or other additives are all conventional materials, such as silicon carbide as the foaming agent.

[0031] Based on municipal sludge with ultra-high admixture content, this invention also proposes a method for preparing foamed cultured stone, including: S1. Pretreatment: The raw materials include municipal sludge, shield tunnel mud, talc and foaming agent. The raw materials are dried, ground and sieved separately, and the sieved material is collected for later use. S2. Dry pressing: Mix the sieved material according to the formula ratio, add water and mix, then dry press to obtain the green body; S3. Firing: The blank is fired to obtain foamed cultural stone products.

[0032] Preferably, in step S3, the firing profile is as follows: heating from room temperature to 500~650℃ for 20~40 min; heating from 500~650℃ to 850~950℃ for 20~40 min, then holding for 40~80 min; heating from 850~950℃ to 1050~1100℃ for 20~60 min, then holding for 70~150 min; heating from 1050~1100℃ to 1150~1170℃ for 20~40 min, then holding for 20~40 min at 1150~1170℃.

[0033] Room temperature generally refers to room temperature, such as 5~35℃.

[0034] In step S2, the water content in the mixture obtained by adding water is preferably 5-10% by mass percentage.

[0035] During the firing process, the time required to reach 850-950℃ (heating + holding) is relatively short, allowing the green body to quickly transition to the medium-temperature zone (i.e., the temperature range between 850-950℃ and 1050-1100℃). The longer residence time within this medium-temperature zone (850-950℃ to 1050-1100℃) facilitates the oxidative decomposition and bonding of the components, resulting in uniform internal and surface temperatures within the green body. This also allows for the full generation and filling of the intergranular gaps with the glass phase, reducing porosity and increasing density and mechanical strength. Compared to conventional cultured stone preparation, this invention extends the firing time (although the total extended time is still shorter than that of foamed ceramics), allowing the extremely high concentration of municipal sludge to fully react with other raw materials, resulting in qualified cultured stone products. It should be noted that, compared with conventional cultured stone, the foamed cultured stone prepared by this invention has the advantage of shorter preparation time. In addition, this invention uses municipal sludge as production raw material, which also has an advantage in production cost. Moreover, this invention consumes a large amount of municipal sludge, which is also beneficial to solving solid waste treatment problems.

[0036] The technical solution of the present invention will be described in detail below with specific embodiments.

[0037] In the following examples and corresponding comparative examples, the municipal sludge used was municipal sludge from the Second Wastewater Treatment Plant of Heshan City, Jiangmen City, Guangdong Province, namely Heshan sludge. Its chemical composition, calculated by mass percentage, was: 17.12% Al₂O₃, 16.49% SiO₂, 1.15% K₂O, 3.80% CaO, 0.46% MgO, 6.22% Fe₂O₃, 0.58% TiO₂, 6.19% P₂O₅, 1.85% SO₃, 0.41% CuO, 0.21% Cr₂O₃, with a loss on ignition of 45.05%, and the remainder being impurities.

[0038] In the following comparative examples, the municipal sludge is Foshan sludge. Its chemical composition, calculated as a percentage by mass, is: 5.52% Al₂O₃, 3.55% SiO₂, 0.24% K₂O, 1.02% Na₂O, 33.31% CaO, 1.96% MgO, 4.74% Fe₂O₃, 0.02% TiO₂, 25.93% SO₃, with a loss on ignition of 19.31%, and the remainder being impurities.

[0039] The shield tunneling mud used is Baiyunshan shield tunneling mud, which includes two types: virgin mud and mixed mud.

[0040] The chemical composition of the virgin mud, calculated by mass percentage, is as follows: 13.69% Al2O3, 72.38% SiO2, 2.15% K2O, 0.24% Na2O, 0.90% CaO, 0.60% MgO, 3.68% Fe2O3, 0.56% TiO2, 0.04% P2O5, 0.97% SO3, 0.01% CuO, 0.01% Cr2O3, with a loss on ignition of 4.72%, and the remainder being impurities.

[0041] The chemical composition of the mixed mud, calculated by mass percentage, is as follows: 14.20% Al2O3, 69.18% SiO2, 2.53% K2O, 0.18% Na2O, 1.64% CaO, 0.82% MgO, 3.99% Fe2O3, 0.58% TiO2, 0.05% P2O5, 1.17% SO3, 0.01% CuO, 0.01% Cr2O3, with a loss on ignition of 5.56%, and the remainder being impurities.

[0042] The talc is commercially available raw talc powder. Calculated by mass percentage, the chemical composition of the talc powder is: 2.67% Al2O3, 60.84% ​​SiO2, 0.69% K2O, 0.07% Na2O, 0.94% CaO, 33.83% MgO, 0.28% Fe2O3, 0.08% TiO2, with a loss on ignition of 0.31%, and the remainder being impurities.

[0043] The raw material formulations (by mass percentage) for the examples are shown in Table 1. The raw material formulations (by mass percentage) for the comparative examples are shown in Table 2.

[0044] Table 1. Raw material formulations for Examples 1-6.

[0045] .

[0046] Table 2. Raw material formulations for Comparative Examples 1-3.

[0047] .

[0048] According to the formula in Table 1, the raw material components are ground, mixed, and mixed with water. They are then pressed into small strips with a diameter of 80 mm and a thickness of 10 mm. The strips are then fired in a small electric furnace. The resulting blanks do not crack or deform, which proves that the use of municipal sludge with extremely high content to develop foamed cultural stone is feasible.

[0049] The electric furnace firing curves are as follows: heating from room temperature to 600℃ for 30 minutes; heating from 600℃ to 900℃ for 30 minutes, and holding at 900℃ for 60 minutes; heating from 900℃ to 1080℃ for 60 minutes, and holding at 1080℃ for 120 minutes; heating from 1080℃ to 1160℃ for 30 minutes, and holding at 1160℃ for 30 minutes.

[0050] The test results of the finished products obtained in Examples 1-6 and Comparative Examples 1-3 are shown in Table 3.

[0051] Hole diameter testing method: Cut off the surface of the cultured stone to make it flat, and use vernier calipers to measure and record the values ​​of the smallest and largest complete holes in the cross section.

[0052] Specific gravity and water absorption test method: The water absorption rate shall be calculated according to the method specified in GB / T 3810.3-2006 "Test methods for ceramic tiles Part III: Determination of water absorption, apparent porosity, apparent relative density and bulk density".

[0053] Shrinkage test method: The marking measurement method is adopted. Markings are made on the sample, and the change in the length of the markings after firing is measured. The shrinkage rate of the firing line is calculated according to the method specified in 6~7 of QB / T 1548-2015.

[0054] Table 3 Test results of Examples 1-6 and Comparative Examples 1-3.

[0055] .

[0056] As shown in Table 3, the formulation of this invention exhibits good stability and can produce qualified cultured stone products. In Examples 1-4, the amount of municipal sludge gradually increases, with a maximum admixture of 93% (based on the mass of the first component). In Example 5, the use of virgin sludge and mixed sludge does not affect the performance of the cultured stone. In Example 6, only mixed sludge is used for tunnel boring machines; the overall silicon content of the raw material formulation is slightly reduced, and the calcium content is slightly increased. This is improved by extending the time between 900℃ and 1080℃, and the product performance still meets the standards.

[0057] In Comparative Example 1, the sludge from Heshan was replaced with sludge from Foshan. Foshan sludge has lower silicon and aluminum content and higher calcium content. Its loss on ignition is lower than that of Heshan sludge, and its theoretical firing temperature is lower than that of Examples 1-6. According to the firing curve of this invention, the high calcium content leads to a narrow firing range of the formula and makes it prone to irregular pores.

[0058] In Comparative Example 2, talc was omitted, and the overall formulation lacked magnesium, which could not form a low-temperature eutectic with silicon and alkali metal oxides in the formulation. The theoretical firing temperature was higher than that of Examples 1-6, and the product was difficult to control according to the firing curve of the present invention.

[0059] In Comparative Example 3, the content of Heshan sludge was increased to 98% (based on the mass of the first component), while the content of shield sludge and talc was reduced, resulting in insufficient silicon and aluminum content in the formula, lack of skeleton elements, and excessive loss on ignition, making the green body prone to bulging and deformation.

[0060] Using the formula of Example 4, 1 kg of raw materials were prepared. After mixing and adding water, the mixture was dry-pressed into a 100 mm × 200 mm × 80 mm lychee-shaped blank. By adjusting the heating curve and the maximum temperature setting, cultured stones of different specific gravities were obtained after firing. The lychee-shaped appearance is the surface decoration effect brought about by the lychee-pattern mold added to the upper layer of the powder during the pressing process.

[0061] In summary, this invention, through firing treatment, can produce foamed cultural stone with a municipal sludge content of 85-93%. The finished product does not crack or deform, effectively solving the problem of "difficult treatment" of municipal sludge and realizing the reuse of solid waste resources with high admixture content.

[0062] The embodiments provided by the present invention have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of the present invention, and the descriptions of the embodiments above are only for the purpose of helping to understand the core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A foamed cultured stone with high content of municipal sludge, characterized in that, The raw materials for preparing foamed cultured stone include a first component and a second component. Based on the mass of the first component, the first component consists of 85-93% municipal sludge, 3-13% shield tunneling mud, and 2-5% talc. The second component includes a foaming agent, and the mass of the second component accounts for 0.05-0.50% of the total mass of the first component.

2. The foamed cultured stone with high content of municipal sludge according to claim 1, characterized in that, Municipal sludge refers to sludge collected from municipal pipelines, with a water content of 50-60%.

3. The foamed cultured stone with high content of municipal sludge according to claim 2, characterized in that, Based on municipal sludge, the elemental composition of municipal sludge, calculated by mass percentage, includes: 5-20% Al2O3, 10-30% SiO2, 1-5% K2O, 1-6% CaO, and 3-10% Fe2O3.

4. The foamed cultured stone with high content of municipal sludge according to claim 1, characterized in that, Shield tunneling mud includes one or both of the following: virgin mud and mixed mud. Virgin mud refers to the original solid waste mud excavated during construction, while mixed mud refers to a mixture of virgin mud and lime.

5. The foamed cultured stone with high content of municipal sludge according to claim 4, characterized in that, Based on virgin mud, the elemental composition of virgin mud, calculated by mass percentage, includes: 10-15% Al2O3, 70-75% SiO2, 1-3% K2O, 0-2% CaO, and 2-5% Fe2O3.

6. The foamed cultured stone with high content of municipal sludge according to claim 4, characterized in that, Based on the mixed mud, the elemental composition of the mixed mud, calculated by mass percentage, includes: 12-15% Al2O3, 65-75% SiO2, 1-5% K2O, 1-3% CaO and 2-5% Fe2O3.

7. The foamed cultured stone with high content of municipal sludge according to claim 1, characterized in that, In talc, the mass percentage of silicon dioxide is ≥60% and the mass percentage of magnesium oxide is ≥30%.

8. The foamed cultured stone with high content of municipal sludge according to claim 1, characterized in that, The foaming agent is silicon carbide powder with a SiC content of ≥99%.

9. A method for preparing foamed cultured stone with high content of municipal sludge, characterized in that, The steps for preparing the foamed cultured stone as described in any one of claims 1-8 are as follows: S1. Pretreatment: The raw materials include municipal sludge, shield tunnel mud, talc and foaming agent. The raw materials are dried, ground and sieved separately, and the sieved material is collected for later use. S2. Dry pressing: Mix the sieved material according to the formula ratio, add water and mix, then dry press to obtain the green body; S3. Firing: The blank is fired to obtain foamed cultural stone products.

10. The preparation method according to claim 9, characterized in that, The firing curves are as follows: In step S3, the firing profile is as follows: from room temperature to 500~650℃, the heating time is 20~40 min; from 500~650℃ to 850~950℃, the heating time is 20~40 min, and then the temperature is held for 40~80 min; from 850~950℃ to 1050~1100℃, the heating time is 20~60 min, and then the temperature is held for 70~150 min; from 1050~1100℃ to 1150~1170℃, the heating time is 20~40 min, and the temperature is held for 20~40 min at 1150~1170℃.