CN112979192B - Preparation method of lightweight aggregate - Google Patents

Abstract

The invention provides a preparation method of lightweight aggregate, which relates to the technical field of preparing non-fired lightweight aggregate or lightweight aggregate by solid wastes, and comprises the following steps: mixing and uniformly grinding a solid waste material, fly ash, metakaolin, a foaming agent and a heavy metal adsorbent; adding water glass solution to granulate into spherical particles; curing the spherical particles by steam, and drying, wherein the curing temperature is 40-180 ℃; the shell is formed on the surface of the spherical particles by a composite slurry prepared by mixing resin, fly ash, a curing agent and a diluent by adopting a spraying process. The invention takes industrial solid wastes as the basis, prepares the porous core by the fly ash and the metakaolin based aluminosilicate material, combines the resin-inorganic composite material coating process, and prepares the light high-strength aggregate for the structure under the condition of no calcination. The cement-free high-energy-consumption cementing material adopts a calcination-free preparation process, and the prepared lightweight aggregate has extremely low water absorption, high cylinder pressure strength, low density and remarkable comprehensive performance.

Description

Preparation method of lightweight aggregate

Technical Field

The invention relates to the technical field of preparing lightweight aggregate or lightweight aggregate from solid wastes, in particular to baking-free lightweight aggregate.

Background

The annual output of the current large industrial solid wastes in China is about 35 hundred million tons, and the historical accumulated stock exceeds600 hundred million tons not only occupy a large amount of land, but also have adverse effects on the environment. The fly ash is a solid waste generated in the production process of coal-fired power plants, and the yield accounts for 5-20% of the total coal-fired quantity. The annual emission amount of the fly ash in China is about 5 hundred million tons, the piling amount of the fly ash in China is more than 20 hundred million tons at present, and the land occupied by an ash storage yard is about 4 multiplied by 10 ⁴ km ² Therefore, the environment is seriously polluted, and a large amount of land resources are occupied. The fly ash contains a large amount of silicon-aluminum oxide, and if the main components in the fly ash are utilized, the waste can be changed into valuable, so that the aim of protecting the environment is fulfilled.

The traditional sandstone materials are exploited in large quantities, waste land resources and destroy ecology, and meanwhile, the density is high, so that the self weight of a building is difficult to reduce. At present, ceramsite is mainly manufactured by raw materials such as clay, shale, fly ash and the like, and most of the ceramsite is prepared by adopting a calcination process, the problems of large factory building investment, complex process technology and high production energy consumption exist in the production of ceramsite by the calcination method, a large amount of carbon emission is generated, and the development of enterprises is severely limited; moreover, the use of a large amount of clay can cause the destruction of cultivated land, which is not beneficial to the sustainable development of the country; the shale ceramsite is greatly influenced by the regional limitation of raw materials, the production process is complex, and the production cost is high; the fly ash ceramsite is mainly prepared by a calcination process, and the cost of the ceramsite is higher. Therefore, the baking-free lightweight aggregate for preparing the structure by using the industrial solid wastes is necessary to be developed and utilized, and the baking-free lightweight aggregate has important significance for the economic benefit and the environmental protection of enterprises.

Most of aggregates prepared by utilizing solid wastes such as mud and waste residues at present have low barrel pressure strength (< 4 MPa), and cannot be used for structural concrete. The methods for preparing the high-strength aggregate are mainly divided into two types: a calcination preparation class and an excitation enhancement class. The patent CN103159483B, CN103922698A, CN108821621A and the like are all prepared by adopting a high-temperature calcination process, the production energy consumption is high, and the process is complex. CN104193248B, CN111170710A, CN105036691B, CN105130235B, CN111205061A, CN1241554A, CN102351557B, CN103496866B and the like adopt chemical excitation modes such as cement, alkali exciting agents, sulfate exciting agents and the like to improve the strength of the aggregate, and the modes have the following problems: (1) The cement belongs to a high-pollution and high-energy-consumption product, the density of the cement in common silicate and aluminosilicate materials is large, the density grade of the prepared ceramsite is high, and the weight of the ceramsite is not favorably reduced; (2) Due to high alkalinity of chemical excitation, the surface of the prepared aggregate is easy to have a saltpetering phenomenon, the water resistance is poor, the durability in directly exposed air is poor, and the overall performance of the aggregate is influenced.

As the ceramsite has an internal porous structure, the water absorption performance of the clay ceramsite is higher than 20%, and the water absorption of the high-strength fly ash ceramsite is higher than 10%, so that the mechanical property of the wet ceramsite is reduced and the application of the wet ceramsite in concrete is influenced due to the overhigh water absorption.

Therefore, the low water absorption lightweight aggregate for the high-strength structure is prepared by a cement-free calcination-free process on the basis of utilizing a large amount of solid wastes, and has important environmental benefits and social benefits.

Disclosure of Invention

The invention takes industrial solid wastes as the basis, prepares the porous core by the fly ash and the metakaolin based aluminosilicate material, combines the resin-inorganic composite material coating process, and prepares the light high-strength aggregate for the structure under the condition of no calcination. The method solves the problem of utilization of industrial solid wastes, and simultaneously, cement-free high-energy-consumption cementing materials adopt a calcination-free preparation process, so that a large amount of carbon emission can be reduced, the environmental benefit is remarkable, and the prepared lightweight aggregate has extremely low water absorption rate, high cylinder pressure strength, low density and remarkable comprehensive performance.

A preparation method of lightweight aggregate comprises the following steps:

(1) Preparing a porous inner core: mixing and uniformly grinding a solid waste material, fly ash, metakaolin, a foaming agent and a heavy metal adsorbent;

(2) Granulating and balling: adding water glass solution until spherical particles are formed;

(3) Temperature excitation: curing the spherical particles obtained in the step (2) by steam, and drying, wherein the curing temperature is 40-180 ℃;

(4) Coating and wrapping a shell: forming a shell on the surface of the spherical particles obtained in the step (3) by adopting a spraying process to prepare composite slurry by mixing resin, fly ash, a curing agent and a diluent;

(5) And (5) naturally curing and forming.

Preferably, the components in the step (1) comprise, by mass, 0-80% of solid waste materials, 10-60% of fly ash, 10-40% of metakaolin, 0.1-0.5% of foaming agents and 0-5% of heavy metal adsorbents.

Preferably, the solid waste material in the step (1) comprises one or more of lead-zinc tailings, biomass combustibles, waste incineration ash, rice hull ash, steel slag, desulfurization ash, stone ore tail mud and sludge.

Preferably, the fly ash in the step (1) is II-grade ash.

Preferably, the fineness of the metakaolin in the step (1) is 1-10 μm.

Preferably, the foaming agent in the step (1) is one or more of aluminum powder and metal silicon powder.

Preferably, the heavy metal adsorbent in step (1) is one or more of sepiolite powder, diatomite and zeolite powder.

Preferably, in the step (2), the water glass is sodium silicate water glass, the molar ratio of silicon dioxide to sodium oxide in the water glass is 1.1-1.5, and the solid content is 10%.

Preferably, the step (2) is carried out by adopting a disk granulator, the inclination angle of a disk is 30-60 degrees, the rotating speed is 20-30r/min, and the mass ratio of liquid to powder in the granulation molding stage is 0.2-0.4.

Preferably, the mass of the composite slurry in the step (4) is 20-40% of the mass of the dried spherical core in the step (3), and the composite ratio of the resin, the fly ash, the curing agent and the diluent is as follows by mass percent: 40-65% of resin, 10-20% of fly ash, 10-20% of curing agent and 10-20% of diluent.

Advantageous effects

The lightweight aggregate of the invention has excellent performance: 1. low aggregate water absorption: the lower water absorption can improve the softening coefficient of the lightweight aggregate, effectively reduce the pre-water saturation time before the lightweight aggregate is used, obviously improve the influence of high water absorption on the water-cement ratio of concrete and the influence of concrete pumping performance of the aggregate, and improve the overall performance of the lightweight aggregate concrete; 2. the overall performance is excellent: the porous core is combined with the high-density composite shell, so that the aggregate has better barrel pressure strength under the same density grade, the surface of the aggregate does not have the phenomenon of saltpetering, and the overall performance is excellent.

Meanwhile, industrial solid wastes are utilized in a large quantity, the raw materials are widely distributed, the cost is low, and the environment is protected; the preparation method does not need the traditional calcination process of more than 1000 ℃, is prepared by a hydrothermal synthesis process, has low production energy consumption within the range of 40-180 ℃, and saves resources; the cement is not needed to be used as a reinforcing material, the sources of the fly ash, the metakaolin and other silicon-aluminum materials are wide, the preparation process is simple, the process is green, and the mechanical property is excellent. The leaching of harmful ions in industrial solid waste can be effectively avoided through the adsorption of hydration products of the internal porous core material and the heavy metal adsorbent to the harmful ions and the outward seepage and interception of the external compact resin-inorganic composite material to the harmful ions.

Drawings

FIG. 1 is a schematic structural view of a lightweight aggregate;

fig. 2 is a cross-sectional photograph of lightweight aggregate.

Detailed Description

A process for preparing the non-sintered light aggregate used to prepare structure from industrial solid wastes includes preparing the porous core material, granulating, activating by temp, coating and natural shaping. (1) preparing a porous core material: firstly, fully grinding and uniformly mixing dry solid waste, fly ash, metakaolin, a foaming agent and a heavy metal adsorbent; (2) granulation and balling: adding core powder material into a disc granulator with a certain inclination angle, and spraying atomized water glass solution on the powder material along with the rotation of the disc until spheres with a certain particle size are formed; and (3) temperature excitation: steam curing the prepared spherical particles at a certain temperature under a curing condition, and then drying moisture; (4) coating and wrapping: pouring the dried aggregate into a disc granulator, and mixing a certain amount of resin, fly ash, a curing agent and a diluent to prepare composite slurry to form a shell on the surface of the aggregate by adopting a spraying process; and (5) naturally curing for 2-3 d and forming.

The solid waste comprises one or more of lead-zinc tailings, biomass comburant, waste incineration ash, rice hull ash, steel slag, desulfurization ash, stone ore tail mud and sludge.

The fly ash is II-grade C-type high-calcium ash;

the fineness of the metakaolin is 1-10 mu m.

The foaming material is one or two of aluminum powder and metal silicon powder;

the heavy metal adsorbent is one or two of sepiolite powder, diatomite and zeolite powder

The compounding mass ratio of the dry solid waste, the fly ash, the metakaolin, the foaming agent and the heavy metal consolidation agent is as follows: 0 to 80 percent of solid waste material, 10 to 60 percent of fly ash, 10 to 40 percent of metakaolin, 0.1 to 0.5 percent of foaming agent and 0 to 5 percent of heavy metal adsorbent.

In the granulation process, sodium silicate water glass is used as water glass liquid, the modulus is 1.1-1.5, and the solid content is 10%;

the inclination angle of the disc is 30-60 degrees, the rotating speed is 21r/min, and the mass ratio of liquid to powder in the granulation molding stage is 0.2-0.4;

the temperature excitation process comprises the following steps: steam curing at 40 ℃ for 4-8 h; then steam curing is carried out for 2-10 h at the temperature of 60 ℃; then steam curing is carried out for 6h at the temperature of 90 ℃; then steam curing at 180 ℃ for 6h; then drying;

the mass of the coating and wrapping material is 20-40% of the dried aggregate;

the compound mass ratio of the resin, the fly ash, the curing agent and the diluent is as follows: 40-65% of resin, 10-20% of fly ash, 10-20% of curing agent and 10-20% of diluent;

the resin is epoxy resin or phenolic resin;

the curing agent is a modified amine curing agent;

the diluent is one or two of trimethylolpropane triglycidyl ether and diethyl phthalate;

the lightweight aggregate prepared by the invention has the particle size of 5-20 mm and the water absorption rate of less than 4 percent, and according to the activity difference of solid waste materials, the obtained aggregate has the cylinder pressure strength of 5-16 MPa and the bulk density of 500-1000 kg/m ³ 。

The modulus refers to the molar ratio of silica to sodium oxide in the water glass.

The solid content refers to the mass percentage of the rest part of the emulsion or the paint in the total amount after drying.

Example 1

The lightweight aggregate preparation material is prepared by mixing 30.8kg of steel slag powder, 4kg of fly ash, 4kg of metakaolin, 1.15kg of sepiolite powder and 0.05kg of aluminum powder, wherein the steel slag powder is purchased from 300-400 meshes of products of Shijiazhuang Yiduo mineral products Limited; the fly ash is purchased from grade II ash of Jianghua electric period capacity power generation Limited company; metakaolin was purchased from 800 mesh products of inner Mongolian Guoyong Kaolin Limited liability company; sepiolite powder was purchased from 600 mesh product of Guangzhou Tuoyi New materials Co., ltd, and aluminum powder was purchased from GLS-67 type product of Jinan Yipeng building materials Co., ltd; the disk pelletizer was purchased from model TDYZ-800, manufactured by the incorporated by reference in the incorporated by reference of the engineering and technology of tongda, of the south of the river.

The above materials were mixed and then pulverized in a ball mill for 20min. The inclination angle of a disc granulator is 45 degrees, the rotation speed is 21r/min, the grinded powder material is added into the granulator, spray granulation molding is carried out by using a water glass solution with the modulus of 1.4 and the solid content of 10 percent, when the particles grow to be about 5-15 mm, the particles are taken out and put into a steam curing box, the curing process is that steam curing is carried out for 6 hours at 40 ℃, steam curing is carried out for 4 hours at 60 ℃, steam curing is carried out for 6 hours at 90 ℃, steam curing is carried out for 6 hours at 180 ℃, and finally drying is carried out at 90 ℃. And (3) continuously putting the dried particles into a disc granulator to roll, forming a shell on the surfaces of the particles by a spraying process on the prepared resin-inorganic composite material slurry, wherein 5.25 parts of epoxy resin, 0.9 part of fly ash, 1.63 parts of trimethylolpropane triglycidyl ether and 1.38 parts of T-33 type curing agent, and then curing at normal temperature for 2d to obtain the finished product of the lightweight aggregate.

Wherein the water glass is purchased from a 3.1 modulus product produced by Tianjin neutralization Shengtai chemical company, and then the modulus is adjusted to 1.4; the epoxy resin is a phoenix brand epoxy resin WSR6101 product; the fly ash is purchased from grade II ash of Jianghua electric period capacitance power generation Limited company; trimethylolpropane triglycidyl ether was purchased from model TMPEG V36 from Senffida chemical Co., ltd, suzhou; the curing agent is a T-33 type product produced by China petrochemical group.

Example 2

The lightweight aggregate preparation material is prepared by mixing 16kg of rice hull ash, 12kg of fly ash, 10kg of metakaolin, 1.92kg of sepiolite powder and 0.08kg of aluminum powder, wherein the rice hull ash is biomass waste generated by calcining ceramsite by Jianhua ceramsite Co., ltd, jiangsu; the fly ash is purchased from grade II ash of Jianghua electric period capacity power generation Limited company; metakaolin was purchased from 800 mesh products of inner Mongolian Guyidong Kaolin Limited liability company; sepiolite powder was purchased from 600 mesh product of Guangzhou Tuoyi New materials Co., ltd, and aluminum powder was purchased from GLS-67 type product of Jinan Yipeng building materials Co., ltd; the disk pelletizer was purchased from model TDYZ-800 manufactured by yota engineering and technology ltd.

The above materials were mixed and then pulverized in a ball mill for 20min. The inclination angle of a disc granulator is 45 degrees, the rotation speed is 21r/min, the grinded powder material is added into the granulator, the water glass solution with the modulus of 1.4 and the solid content of 10 percent is used for spray granulation molding, when the particles grow to about 5-15 mm, the particles are taken out and put into a steam curing box, the curing process is 40 ℃ steam curing for 6h, then 60 ℃ steam curing for 4h, then 90 ℃ steam curing for 6h, then 180 ℃ steam curing for 6h, and finally 90 ℃ drying is carried out. And (2) continuously putting the dried particles into a disc granulator to roll, forming a shell on the surface of the particles by using a spraying process on the prepared resin-inorganic composite material slurry, wherein 6kg of epoxy resin, 2kg of fly ash, 2kg of trimethylolpropane triglycidyl ether and 2kg of T-33 type curing agent, and then curing at normal temperature for 2d to obtain the finished product of the lightweight aggregate.

Wherein the water glass is purchased from a 3.1 modulus product produced by Tianjin neutralization Shengtai chemical industry Co., ltd, and then the modulus is adjusted to 1.4; the epoxy resin is a product of a phoenix brand epoxy resin WSR6101 type; the fly ash is purchased from grade II ash of Jianghua electric period capacity power generation Limited company; trimethylolpropane triglycidyl ether was purchased from model TMPEG V36 from Senffida chemical Co., ltd, suzhou; the curing agent is T-33 type product produced by Chinese petrochemical group.

Example 3

The lightweight aggregate preparation material is prepared by mixing 14kg of stone ore tail mud, 12kg of fly ash, 12kg of metakaolin, 1.88kg of diatomite and 0.12kg of metal silicon powder, wherein the stone ore tail mud is industrial tail mud generated in the aggregate processing process of the Xinyuan stone breaking limited company; the fly ash is purchased from grade II ash of Jianghua electric period capacitance power generation Limited company; metakaolin was purchased from 800 mesh products of inner Mongolian Guyidong Kaolin Limited liability company; the diatomite is purchased from Jilin Yuantong mining company Limited to produce 325 mesh products; the metal silicon powder is purchased from 325-mesh products of Chuangying metal materials Co., ltd, qinghe county; the disk pelletizer was purchased from model TDYZ-800, manufactured by the incorporated by reference in the incorporated by reference of the engineering and technology of tongda, of the south of the river.

The above materials were mixed and then pulverized in a ball mill for 20min. The inclination angle of a disc granulator is 35 degrees, the rotating speed is 21r/min, powder materials are added into the granulator, spray granulation molding is carried out by using a water glass solution with the modulus of 1.4 and the solid content of 10%, when the particles grow to be about 5-15 mm, the particles are taken out and put into a steam curing box, the curing process is steam curing at 40 ℃ for 6h, then steam curing at 60 ℃ for 6h, then steam curing at 90 ℃ for 6h, then steam curing at 180 ℃ for 8h, and finally drying at 90 ℃. And (2) continuously putting the dried particles into a disc granulator to roll, forming a shell on the surface of the particles by using the prepared resin-inorganic composite material slurry, wherein 8kg of epoxy resin, 1.92kg of fly ash, 1.8kg of diethyl phthalate and 1.52kg of T-32 type curing agent through a spraying process, and then curing at normal temperature for 2d to obtain a finished product of the lightweight aggregate.

Wherein the water glass is purchased from a 3.1 modulus product produced by Tianjin neutralization Shengtai chemical company, and then the modulus is adjusted to 1.4; the epoxy resin is a product of a phoenix brand epoxy resin WSR6101 type; the fly ash is purchased from grade II ash of Jianghua electric period capacity power generation Limited company; diethyl phthalate is a product of Tay chemical Co Ltd in the tin-free market; the curing agent is a T-32 type product produced by China petrochemical group.

Example 4

The lightweight aggregate preparation material is prepared by mixing 23.96kg of fly ash, 16kg of metakaolin and 0.04kg of metal silicon powder, wherein the fly ash is purchased from grade II ash of Jianghua electric power generation Limited company; metakaolin was purchased from 800 mesh products of inner Mongolian Guoyong Kaolin Limited liability company; the metal silicon powder is purchased from 325-mesh products of Chuangying metal materials Co., ltd, qinghe county; the disk pelletizer was purchased from model TDYZ-800 manufactured by yota engineering and technology ltd.

The above materials were mixed and then pulverized in a ball mill for 20min. The inclination angle of a disc granulator is 35 degrees, the rotating speed is 21r/min, powder materials are added into the granulator, spray granulation molding is carried out by using a water glass solution with the modulus of 1.2 and the solid content of 10%, when the particles grow to be about 5-15 mm, the particles are taken out and put into a steam curing box, the curing process is steam curing at 40 ℃ for 6h, then steam curing at 60 ℃ for 6h, then steam curing at 90 ℃ for 6h, then steam curing at 180 ℃ for 8h, and finally drying at 90 ℃. And (3) continuously putting the dried particles into a disc granulator to roll, forming a shell on the surfaces of the particles by using a spraying process for the prepared resin-inorganic composite material slurry, wherein 9.6kg of epoxy resin, 1.6 kg of fly ash, 2.8 kg of diethyl phthalate and 2 g of T-32 type curing agent, and then curing at normal temperature for 2d to obtain a finished lightweight aggregate.

Wherein the water glass is purchased from a 3.1 modulus product produced by Tianjin neutralization Shengtai chemical company, and then the modulus is adjusted to 1.2; the epoxy resin is a product of a phoenix brand epoxy resin WSR6101 type; the fly ash is purchased from grade II ash of Jianghua electric period capacity power generation Limited company; diethyl phthalate is a product of Tay chemical Co Ltd in the tin-free market; the curing agent is a T-32 type product produced by China petrochemical group.

The aggregate performance detection method adopts GB/T17431-2010 light aggregate and test method thereof; harmful ion leaching is carried out by oscillating and stirring 10g of aggregate sample in 100ml of distilled water for 24h, filtering, and detecting the content of harmful ions in the filtered water by adopting an atomic absorption spectrometry. The test results are shown in table 1:

table 1 lightweight aggregate performance test results

Apparent density refers to the ratio of the mass to the apparent volume of a material; bulk density the mass per unit volume measured immediately after filling of a container into which dust or powder is freely filled. The density tests are carried out according to GB/T17431-2010 lightweight aggregate and test method thereof.

The strength growth mechanism: compared with the traditional high-temperature calcination theory for preparing the lightweight aggregate, the method has the advantages that the chemical auxiliary agent, namely the liquid sodium silicate, is used for exciting the aluminosilicate minerals in the fly ash, the metakaolin and the solid waste materials, and the polymer with good gelling activity is formed through depolymerization and repolymerization curing reaction; by combining with a foaming agent, namely aluminum powder, metal silicon powder and the like, under an alkaline environment (in the preparation method, the aluminosilicate such as the water glass excited fly ash is alkaline, and independent pH adjustment is not needed), a polymeric porous structure is formed, so that the apparent density of the inner core is reduced; the degree of polymer reaction is further improved by a hydrothermal synthesis process, i.e. steam curing, thereby forming a porous core with good strength. By combining with the shell layer enhancement theory, the compact and high-strength resin-fly ash composite slurry (the shell in figure 1) is formed by coating the structure on the surface of the inner core, so that the cylinder pressure strength and the water absorption of the lightweight aggregate are obviously improved. Therefore, by comparing table 1 and table 2, it can be found that the lightweight aggregate prepared by the present invention has higher barrel pressure strength when the density grades are the same.

The light weight mechanism is as follows: (1) The density of materials such as fly ash, metakaolin and the like is obviously lower than that of cementing materials such as cement, mineral powder and the like; (2) The porous inner core is formed through chemical foaming of metal powder, so that the apparent density is obviously reduced; (3) The apparent density of the resin-fly ash composite slurry (resin-inorganic composite compact shell in figure 1) is significantly lower than that of the cement-based inorganic cementing material, and the invention adopts a chemical excitation principle instead of a calcination process, so that the apparent density is lower when the product has the same cylinder pressure strength as the aggregate in the prior art.

The harmful metal consolidation mechanism is as follows: (1) The three-dimensional network polymer structure formed by aluminosilicate materials such as fly ash and metakaolin through chemical excitation can combine most harmful ions; (2) the heavy metal adsorbent can effectively adsorb heavy metal ions; (3) The dense resin-fly ash composite slurry (shell in fig. 1) effectively blocks the leaching of harmful ions from the inner core.

The properties of the commercial homogeneous grade aggregate product prepared by the high temperature calcination process are shown in table 2:

table 2 commercial aggregate performance test results

The comparison shows that compared with the calcined aggregate with the same density grade sold in the market, the aggregate prepared by the invention has the advantages that the cylinder compressive strength can be improved by more than 50 percent, and the water absorption rate is extremely low; meanwhile, a large amount of industrial solid waste can be utilized, harmful ions in the industrial solid waste can be effectively consolidated, and application approaches of the industrial solid waste are greatly widened.

Claims (5)

1. A preparation method of lightweight aggregate comprises the following steps:

(1) Preparing a porous inner core:

according to the mass percentage, 0-80% of solid waste material, 10-60% of fly ash, 10-40% of metakaolin, 0.1-0.5% of foaming agent and 0-5% of heavy metal adsorbent are mixed and milled uniformly; the solid waste material comprises one or more of lead-zinc tailings, biomass combustion materials, waste incineration ash, rice hull ash, steel slag, desulfurization ash, stone ore tail mud and sludge; the foaming agent is one or more of aluminum powder and metal silicon powder;

(2) Granulating and balling: adding water glass solution to granulate into spherical particles; the granulation and balling are carried out by adopting a disc granulator, the inclination angle of a disc is 30-60 degrees, the rotating speed is 20-30r/min, and the mass ratio of liquid to powder in the granulation and molding stage is 0.2-0.4;

(3) Temperature excitation: curing the spherical particles obtained in the step (2) by steam, and drying, wherein the curing temperature is 40-180 ℃;

(4) Coating and wrapping a shell: pouring the dried aggregate into a disc granulator, and mixing 40-65% of resin, 10-20% of fly ash, 10-20% of curing agent and 10-20% of diluent by mass percent to prepare composite slurry, wherein a shell is formed on the surface of the spherical particle obtained in the step (3) by adopting a spraying process, and the mass of the composite slurry is 20-40% of that of the spherical core dried in the step (3);

(5) And (5) naturally curing and forming.

2. The method according to claim 1, wherein the fly ash in the step (1) is class II ash.

3. The method according to claim 1, wherein the fineness of metakaolin in the step (1) is 1 to 10 μm.

4. The preparation method according to claim 1, wherein the heavy metal adsorbent in step (1) is one or more of sepiolite powder, diatomite powder and zeolite powder.

5. The method according to claim 1, wherein the water glass in the step (2) is sodium silicate water glass, the molar ratio of silica to sodium oxide in the water glass is 1.1 to 1.5, and the solid content is 10%.

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