CN107500799B - Preparation method of light sludge-fly ash porous ceramic - Google Patents

Abstract

The invention discloses a preparation method of lightweight sludge-fly ash porous ceramics. The raw materials of municipal sludge, first-grade fly ash, starch, CaCO ₃ and bentonite are wet-milled in tap water to prepare slurry, and the slurry is prepared by wet grinding. The slurry is injected into the mold with a certain moisture content, and is demolded after drying for a period of time. Then, the embryo body is placed in a sintering furnace for pressureless sintering, and taken out after heat preservation to obtain the sludge-fly ash porous ceramic. In the invention, the sludge taken out from the sewage treatment plant is directly put into production, a process of drying and screening is omitted, and the cost is reduced without affecting the performance of ceramics. The method has the advantages of cheap raw materials, simple operation, high reproducibility, safety and reliability in the preparation process, fast heating rate, low sintering temperature and simple procedure during preparation, and the prepared ceramic has a large porosity, which greatly improves the preparation of sludge-fly ash porous ceramics. s efficiency.

Description

A kind of preparation method of light sludge-fly ash porous ceramics

technical field

The invention belongs to the field of porous ceramics preparation, in particular to a preparation method of light sludge-fly ash porous ceramics.

Background technique

With the increasing shortage of natural resources and the challenge of sustainable development, the research and utilization of aluminum-silicon waste is of great significance. Fly ash is the waste discharged from thermal power stations, and municipal sludge is the waste produced by sewage treatment, which is a usable waste resource. The composition of fly ash and municipal sludge is mainly SiO ₂ , Al ₂ O ₃ and CaO, which can be used to prepare porous ceramics.

At present, there are many methods for preparing ceramics with fly ash and municipal sludge as the main ceramic raw materials. For example, Zhao et al., using equal components of fly ash, municipal sludge and clay, prepared a fly ash, municipal sludge and clay composite ceramic particles and clay-based ceramic particles at 1100 °C. It is used for sewage treatment when added to the biological filter. Tests show that the porosity of ceramic particles prepared by using fly ash, municipal sludge and clay composite is higher than that of clay base, and the effect of sewage filtration treatment is better (Zhao Y. , et al. Research on sludge-fly ash ceramic particles (SFCP) for synthetic and municipal wastewater treatment in biological aerated filter (BAF), Bioresource technology, 2009, 100(21): 4955-4962). Xu Peng designed a scheme: when the amount of CaCO ₃ is 30%, sintered at 1150 °C, and kept for 30 minutes, the ratio of fly ash urban sludge is 3:2, bentonite is 3%, and sodium silicate is 1.5%. The prepared porous The total porosity of the ceramic product was 67.29%, and the bulk density was 1.06 g/cm ³ . (Xu Peng. Study on the preparation of porous ceramic materials from fly ash-urban sludge and its properties [D]. Jiangsu University, 2015.), during preparation, several ingredients are mixed in a dry state and pressed into a tablet machine at 13MPa. The method we adopted can be formed without pressure, and can be used directly with a certain moisture content when the sludge leaves the factory, which saves the cost of drying the sludge once, and can adjust the shape of the particles; when choosing a pore-forming agent, according to its pore-forming mechanism. Mixing two pore-forming agents with different options forms pores in two stages, making the ceramics less dense and more porous, and at the same time improving the cracking of the ceramics during the sintering process. In the process of sewage treatment, light ceramsite with low density can save energy during backwashing, and large porosity is more conducive to microbial attachment.

Therefore, it is very necessary to develop a method for preparing lightweight sludge-fly ash porous ceramics, which is of great significance for further utilizing municipal waste and responding to the national strategic policy of energy conservation and emission reduction.

SUMMARY OF THE INVENTION

Purpose of the invention: In view of the problems existing in the prior art, the technical problem to be solved by the present invention is to provide a kind of preparation of sludge-fly ash porous ceramic material with low density, uniform grain size, low cost and simple and easy preparation method method.

In order to solve the above-mentioned technical problems, the present invention adopts the following technical scheme: a preparation method of sludge-fly ash porous ceramics, comprising the following steps:

(1) Mix sludge, fly ash, starch, CaCO ₃ and bentonite in a mass ratio of 1.5-2.5:3-4:0.35-1.2:0.35-1.:2:0.2-0.4 and add water to stir, fully After mixing, the slurry is obtained; in one embodiment, the sludge can be selected from municipal sludge, and the factory sludge (water content 47.5%) can be directly put into use;

(2) injecting the slurry obtained in step (2) into the mold, stirring and driving out the air bubbles therein, after fully filling the mold, drying, and demoulding the embryo after it becomes hard, so that the embryo has no appearance defects;

(3) The embryo body is put into a sintering furnace for high temperature pressureless sintering, and taken out after heat preservation to obtain a sludge-fly ash porous ceramic. Preferably, in step (3), the dried mud material is demolded without cracks, and the diameter of the embryo body is 12 mm, which can be adjusted according to different molds.

Preferably, the sludge, fly ash, starch, CaCO ₃ and bentonite are mixed in a mass ratio of 1.75-2.16: 3.15-3.6: 0.35-1.05: 0.35-1.05: 0.21-0.35.

Preferably, in step (1), the sludge is based on the mass of dry sludge, wherein the amount of water added is 55% to 65% of the total mass of sludge, fly ash, starch, CaCO ₃ and bentonite. The quality of the water added here is determined by many experiments to ensure that the mud has a certain fluidity and is injected into the mold. If the fluidity is too large or too small, the molding will be affected.

Preferably, the sludge is directly from a sewage treatment plant, which is dried in the sun, pulverized by a pulverizer, and then sieved to obtain sludge powder and put into use; or directly put into use sludge from the factory. Wherein, the average particle size of the sludge powder is 100-200 mesh. If used directly, after adding water to the sludge to a moisture content of 60% to 70%, the large particles in the sludge can be removed by natural precipitation.

Preferably, in step (2), drying is performed at a temperature of 60-90° C. for 20-30 minutes. The purpose of drying here is to make the embryo body no longer fluid and have no effect on the performance of the finished product. Do not boil the free water in the embryo body during the drying process. The dried mud is demoulded without cracks, and the diameter of the embryo can be adjusted according to the different molds.

In step (3), the sintering furnace is a box-type sintering furnace, and the sintering is divided into two stages, both of which are heated at a uniform speed, and the sintering process is:

The first stage: 3 to 4°C/min at 0°C to 600°C and then kept for 15 to 30 minutes;

The second stage: 2.8 to 3.5 °C/min at 600 to 1130 °C, and kept for 10 to 30 minutes.

Preferably, in step (3), the heating rate during sintering is 0-600°C for 3 hours, and the temperature is kept for 30 minutes;

Beneficial effects: Compared with the prior art, the present invention provides a method for preparing sludge-fly ash porous ceramics with simple operation, high reproducibility, safety, reliability, space saving, energy and low cost. The method we adopt can be formed without pressure, and can be used directly with a certain moisture content when the sludge leaves the factory, which saves the cost of one-time sludge drying, and can adjust the shape of the particles; when choosing a pore-forming agent, according to its pore-forming mechanism The choice of mixing two pore formers to form pores in two stages makes the ceramics less dense and porosity larger, and at the same time improves the cracking of the ceramics during the sintering process. The invention has fast heating rate, low sintering temperature and simple procedure during preparation, the prepared sludge-fly ash porous ceramic has smooth surface without gaps and large porosity, and greatly improves the efficiency of preparing sludge-fly ash porous ceramic.

Description of drawings

Figure 1 shows the SEM surface topography of municipal sludge at 1000°C sintering temperature (magnified 5000 times);

The developed pore structure shows the feasibility of making porous ceramics from sludge;

Figure 2 is the SEM surface topography of the sludge-fly ash porous ceramics at a sintering temperature of 1130°C in Example 1 (magnified 5000 times); many pores can be seen on the cross-section of the finished product, indicating that the preparation is successful;

Figure 3 is a schematic view of the appearance of the finished product.

Detailed ways

In the following examples, the sludge is municipal sludge, and the municipal sludge is taken from the sewage treatment plant of the Academy of Sciences, Jiangning District, Nanjing City, for laboratory storage, the above-mentioned sludge is dried in the sun, crushed and sieved with a pulverizer, Collect powder; or directly put the factory sludge (moisture content 47.5%) into use; fly ash is taken from Ma'anshan Wanneng No. 1 Power Plant.

Example 1

Take the original urban sludge that has just left the factory, and mix it with fly ash, starch, bentonite and water according to 2.1:3.15:1.4:0.35:4 (the sludge is calculated according to the mass of dry sludge, and the ratio is the mass ratio). Pour the slurry into the mold and use a glass rod to drive out the air bubbles, put it in a drying oven at 70°C for half an hour, take it out and demould, put it in a crucible and put it in a box-type sintering furnace; 3.3°C/min at 0-600°C, then keep warm for 20min ; 3.5°C/min at 600-1140°C for 30min. Its apparent porosity was 59%, and its bulk density was 1.04 g/cm ³ .

Example 2

Take the original municipal sludge that has just left the factory, mix it with fly ash, CaCO ₃ and water according to 2.1:3.15:1.75:4 and stir evenly (here the sludge is calculated according to the mass of dry sludge, and the ratio is the mass ratio). Pour the slurry into the mold and use a glass rod to drive out the air bubbles, put it in a drying oven at 70°C for half an hour, take it out and demould, put it in a crucible and put it in a box-type sintering furnace; 3.3°C/min at 0-600°C, then keep warm for 20min ; 3.5°C/min at 600-1140°C for 30min. Its apparent porosity is 61% and its bulk density is 1.05g/cm3.

Example 3

Take the original urban sludge that has just left the factory, and mix it with fly ash, starch, bentonite and water according to 2.1:3.15:1.4:0.35:4 (the sludge is calculated according to the mass of dry sludge, and the ratio is the mass ratio). Pour the slurry into the mold and use a glass rod to drive out the air bubbles, put it in a drying oven at 70°C for half an hour, take it out and demould, put it in a crucible and put it in a box-type sintering furnace; 3.3°C/min at 0-600°C, then keep warm for 20min ; 3.5°C/min at 600～1130°C, keep warm for 30min. Its apparent porosity was 53%, and its bulk density was 0.97 g/cm ³ .

Example 4

Take the original urban sludge that has just left the factory, and mix it with fly ash, starch, bentonite and water according to 2.1:3.15:1.4:0.35:4 (the sludge is calculated according to the mass of dry sludge, and the ratio is the mass ratio). Pour the slurry into the mold and use a glass rod to drive out the air bubbles, put it in a drying oven at 70°C for half an hour, take it out and demould, put it in a crucible and put it in a box-type sintering furnace; 3.3°C/min at 0-600°C, then keep warm for 20min ; 3.5°C/min at 600-1130°C for 10min. Its apparent porosity was 49%, and its bulk density was 0.86 g/cm ³ .

In this case, the bulk density of the sample is the smallest among all cases, but when the starch content reaches 20% of the total mass (excluding moisture), because the organic content is too high, cracking is likely to occur in the first stage of heating, and the repetition rate of this set of data is also low, which is not conducive to actual production.

Example 5

Take the original urban sludge that has just left the factory, mix it with fly ash, starch, CaCO ₃ , bentonite and water according to 1.75:3.5:1.05:0.35:0.21:4 (the sludge is calculated according to the dry sludge mass, and the ratio is is the mass ratio). Pour the slurry into the mold and use a glass rod to drive out the air bubbles, put it in a drying oven at 70°C for half an hour, take it out and demould, put it in a crucible and put it in a box-type sintering furnace; 3.3°C/min at 0-600°C, then keep warm for 20min ; 3.5°C/min at 600-1130°C for 20min. Its apparent porosity was 61%, and its bulk density was 1.02 g/cm ³ .

Example 6

Take the original urban sludge that has just left the factory and mix it with fly ash, starch, CaCO ₃ , bentonite and water according to 1.75:3.5:0.7:0.7:0.21:4 (the sludge is calculated according to the mass of dry sludge, and the ratio is is the mass ratio). Pour the slurry into the mold and use a glass rod to drive out the air bubbles, put it in a drying oven at 70°C for half an hour, take it out and demould, put it in a crucible and put it in a box-type sintering furnace; 3.3°C/min at 0-600°C, then keep warm for 20min ; 3.5°C/min at 600-1130°C for 20min. Its apparent porosity was 64%, and its bulk density was 0.93 g/cm ³ .

With this production method, the finished product has good appearance without cracks, and the porosity and density are excellent, so it is the best case.

Example 7

Take the original municipal sludge that has just left the factory, and mix it with fly ash, starch, CaCO ₃ , bentonite and water according to 1.75:3.5:0.35:1.05:0.21:4 (the sludge is calculated according to the dry sludge mass, and the ratio is is the mass ratio). Pour the slurry into the mold and use a glass rod to drive out the air bubbles, put it in a drying oven at 70°C for half an hour, take it out and demould, put it in a crucible and put it in a box-type sintering furnace; 3.3°C/min at 0-600°C, then keep warm for 20min ; 3.5°C/min at 600-1130°C for 20min. Its apparent porosity was 59%, and its bulk density was 1.08 g/cm ³ .

Claims (5)

1. The preparation method of the light sludge-fly ash porous ceramic is characterized by comprising the following steps:

(1) mixing sludge, fly ash, starch and CaCO₃Mixing bentonite according to the mass ratio of 1.5-2.5: 3-4: 0.35-1.2: 0.2-0.4, adding water, stirring, and fully mixing to obtain slurry;

(2) injecting the slurry obtained in the step (1) into a mold, stirring to drive air bubbles in the slurry, drying at the temperature of 60-90 ℃ for 20-30 minutes after the mold is fully filled, and demolding after the blank becomes hard to ensure that the blank has no appearance defects;

(3) the blank body is placed into a sintering furnace for high-temperature pressureless sintering, the sintering furnace is a box-type sintering furnace, the sintering is divided into 2 stages, the temperature is raised at a constant speed, and the sintering process is as follows:

the first stage is as follows: 3-4 ℃/min at 0-600 ℃, and then preserving heat for 15-30 min;

and a second stage: 2.8-3.5 ℃/min at 600-1130 ℃, and taking out after heat preservation for 10-30 min to obtain the sludge-fly ash porous ceramic.

2. The method according to claim 1, wherein the sludge, fly ash, starch, CaCO₃And the bentonite is mixed according to the mass ratio of 1.75-2.16: 3.15-3.6: 0.35-1.05: 0.21-0.35.

3. The method according to claim 1 or 2, wherein in the step (1), the sludge is measured by dry sludge mass, and the water is added into the sludge, fly ash, starch and CaCO₃And 55 to 65 percent of the total mass of the bentonite.

4. The preparation method according to claim 1, wherein the sludge is sludge directly from a sewage treatment plant, is dried in the sun, is crushed by a crusher, is sieved to obtain sludge powder, and is put into use; or directly putting the factory sludge into use.

5. The method according to claim 4, wherein the average particle size of the sludge powder is 100 to 200 mesh.

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