Preparation method of high specific strength low-silicon solid waste ceramsite

Abstract

The invention discloses a preparation method of high specific strength low-silica solid waste ceramsite. The method dries, grinds, mixes and granulates raw materials including mining and metallurgical solid waste to obtain green ceramsite blanks, and the green ceramsite blanks are sintered to obtain solid waste ceramsite. The method uses mining and metallurgical solid waste raw materials with low silicon, high aluminum and high iron. By controlling the sintering conditions, high specific strength low-silica solid waste ceramsite with a strength grade ≥ 33 MPa, a bulk density ≤ 910 kg / m<supgt;3< / supgt; and a specific strength ≥ 36 MPa / (g / cm<supgt;3< / supgt;) is obtained, breaking through the limitation of the traditional ceramsite on the requirement of high silicon oxide content, greatly increasing the addition amount of high-aluminum and high-iron solid waste raw materials, and improving the performance of the solid waste ceramsite at the same time.

Description

Technical Field

[0001] The present invention relates to a preparation method of solid waste ceramsite, in particular to a method for preparing high specific strength by using low-silica solid waste, and belongs to the technical field of solid waste resource utilization. Background Art

[0002] Density and strength are the two most important properties of ceramsite as concrete aggregate. However, the two usually restrict each other. When the batching is the same and the sintering process is the same, the aggregate with higher density has greater strength, and the aggregate with lower density has smaller strength. Improving the high specific strength of ceramsite reduces the bearing pressure of concrete, which greatly expands the application fields of ceramsite in high-rise buildings, bridges and other high-bearing buildings. Preparing high-quality ceramsite from solid waste is a very promising way of resource utilization. In the related technologies of preparing ceramsite from solid waste, Chinese Patent CN115557775A discloses a method for preparing 100% solid waste ceramsite by using titanium tailings, municipal solid waste incineration fly ash and waste glass as raw materials; Chinese Patent CN115259885A discloses bauxite tailing sintered ceramsite prepared by using bauxite tailings, paper-making sludge and modified phosphorus slag under the condition of a mass ratio of 48-110:18-42:20, so that the contents of various components such as SiO2, Al2O3, Fe2O3, CaO and MgO in the mixture meet the content range required for high-strength and low-density ceramsite, thereby ensuring that the cylinder compressive strength of the sintered ceramsite reaches 10-12 MPa; Chinese Patent CN113480325A discloses a building ceramsite based on fluorite tailings and a preparation method thereof, specifically discloses using 60-80 parts of fluorite tailings, 10-20 parts of clay, 10-20 parts of kaolin and 0.5-1.0 part of foaming agent to prepare tailings ceramsite. Although these patented technologies have achieved a high dosage of solid waste in the process of preparing ceramsite, there are few similar prior arts on how to simultaneously meet the light weight and high strength of ceramsite and improve the specific strength of ceramsite. Summary of the Invention

[0003] To solve the above technical problems, the purpose of the present invention is to provide a preparation method of low-silica solid waste ceramsite with high specific strength. This method uses low-silica solid waste raw materials and can combine the control of firing conditions to obtain low-silica solid waste ceramsite with high specific strength and spinel as the main skeleton structure, breaking through the limitation of the traditional ceramsite aggregate on the requirement of high silicon oxide content, greatly increasing the usage proportion of high-aluminum and high-iron solid waste raw materials, and at the same time, the obtained ceramsite has excellent properties of high strength and light weight, and has a wider application prospect.

[0004] To achieve the above technical purpose, the present invention provides a preparation method of low-silica solid waste ceramsite with high specific strength. The preparation method is to dry, grind, mix and granulate raw materials including mining and metallurgy solid waste to obtain a green ceramsite body, and sinter the green ceramsite body to obtain solid waste ceramsite;

[0005] The main components in the raw materials satisfy: the SiO2 content ≤ 45 wt%, 35 wt% ≤ the content of Al2O3 + Fe2O3 ≤ 60 wt%, and the CaO content ≤ 5 wt%.

[0006] The sintering regime satisfies: heating and sintering at a heating rate ≤ 15 °C / min, holding at 400 - 600 °C for 0.5 - 3 hours, then holding at 1000 - 1400 °C for 10 - 120 min, and then cooling; among them, when the temperature rises above 400 °C, the sintering is carried out in a reducing atmosphere.

[0007] The solid waste ceramsite of the present invention uses low-silica solid waste as the main raw material, or these raw materials mainly contain components such as Al2O3 + Fe2O3, while the SiO2 content is relatively low. Under the combined special sintering process conditions, these raw materials undergo phase reconstruction and are transformed into phases mainly composed of spinel structures such as Al2FeO4 and Mg 0.7 Fe 0.23 Al 1.97 O4, etc. The ceramic skeleton composed of these phases replaces the traditional mullite ceramic skeleton and has the characteristics of light weight and high strength.

[0008] As a preferred scheme, the main components in the raw materials satisfy: 35 wt% ≤ the SiO2 content ≤ 45 wt%, 45 wt% ≤ the content of Al2O3 + Fe2O3 ≤ 55 wt%, and 3 wt% ≤ the CaO content ≤ 5 wt%. The proportion of mineral and metallurgical solid waste in the raw materials of the present invention is at least 90% or more, and various mineral and metallurgical solid wastes can be combined to meet the composition requirements.

[0009] As a preferred scheme, the mineral and metallurgical solid waste includes at least one of tailings, red mud, fly ash, slime, coal gangue, and steel slag. The main components of these mineral and metallurgical solid wastes are SiO2, Al2O3, Fe2O3, etc., and these mineral and metallurgical solid wastes can be used in combination according to the needs of the raw material composition.

[0010] As a preferred scheme, the mineral and metallurgical solid waste is ground to a particle size of less than 150 mesh. Grinding the mineral and metallurgical solid waste to an appropriate particle size is beneficial to improving the reaction activity of the mineral and metallurgical solid waste particles and improving the subsequent solid-phase reaction effect.

[0011] As a preferred solution, the sintering regime satisfies the following: heating and sintering are carried out at a heating rate of 8 - 15 °C / min, holding at 400 - 500 °C for 1 - 3 hours, then holding at 1200 - 1300 °C for 50 - 100 min, and then cooling; wherein, when the temperature rises above 400 °C, the sintering is carried out in a reducing atmosphere. The holding platform at 400 - 500 °C enables the slow release of gases such as CO and CO2 produced by the sintering of C, organic matter, etc., making the pores of the ceramsite small and uniform, which is beneficial for the ceramsite to obtain a good internal structure. If the heating rate is too fast or the holding is carried out at a low temperature, the generation and release of gases at high temperature will be intense, resulting in uneven pores or breaking through the internal structure, leading to a decrease in the specific strength of the ceramsite. The holding platform at 1200 - 1300 °C enables the pore-forming agents such as SiC to fully react, making the gas generate smoothly without breaking through the surface of the pellet, obtaining uniform pores and a good expansion effect, and making the ceramsite have a lower density. The reducing atmosphere at high temperature helps the stable formation of the spinel phase, enabling the ceramsite to obtain a high-strength framework structure, thus obtaining a higher specific strength.

[0012] As a preferred solution, p(O2) ≤ 0.1 atm in the reducing atmosphere.

[0013] As a preferred solution, the reducing atmosphere is provided by carbon, biomass or CO gas.

[0014] As a preferred solution, the cooling is carried out by furnace cooling, controlling the cooling rate ≤ 10 °C / min and cooling to below 700 °C. Gentle cooling of the ceramsite is beneficial for the close intergrowth and uniform formation of phases, avoiding internal structure defects caused by the severe shrinkage of individual phases, thereby reducing the specific strength of the ceramsite.

[0015] Compared with the prior art, the beneficial effects brought by the technical solution of the present invention are as follows:

[0016] 1) The technical solution of the present invention can obtain ceramsite with high specific strength from low-silica solid waste raw materials, breaking through the limitation of the traditional ceramsite aggregate on the requirement of high silicon oxide content, thereby enabling the full and reasonable utilization of alumina and iron oxide in the solid waste, and greatly increasing the addition amount of high-aluminum and high-iron materials such as red mud and aluminum ash in the raw material batching process.

[0017] 2) The technical solution of the present invention changes the traditional aluminum-silicon-based mullite ceramic framework and establishes a new type of aluminum-iron-based high-hardness spinel ceramic framework, which has the characteristics of light weight and high strength, providing ideas for the development and performance improvement of new ceramics.

[0018] 3) The low-silica solid waste ceramsite of the technical solution of the present invention has excellent properties of high strength and light weight, and the specific strength ≥ 36 MPa / (g / cm 3 ), greatly broadening the application scenarios of the ceramsite. Description of the Drawings

[0019] Figure 1 XRD comparison chart of the phases of low-silica ceramsite and high-silica ceramsite.

[0020] Specific implementation manners

[0021] The following examples are intended to further illustrate the content of the present invention rather than limit the protection scope of the claims of the present invention.

[0022] Example 1

[0023] Using a flotation tailings from a certain place in Hunan and a de-alkalized red mud from a certain place in Shandong as the main raw materials (the SiO2 content in the tailings is 69%, the Al2O3 content is 12%, the Fe2O3 content is 4%, and the other components are 15%; the SiO2 content in the de-alkalized red mud is 24%, the Al2O3 content is 22%, the Fe2O3 content is 43%, and the balance is other components such as organic matter), the mixed raw meal is formulated according to the SiO2 content of 40%, the sum of the Al2O3 + Fe2O3 content of 51%, and the CaO content of 3%. After batching, it is dried, ground to less than 150 mesh and mixed evenly. The mixture is granulated by a disk granulator to obtain green balls. The green balls are sintered: the heating rate = 12°C / min, it needs to be kept warm for 2 h in the 450°C interval, control the reducing atmosphere at a temperature above 400°C so that p(O2) = 0.01 atm, keep warm at 1250°C in the high-temperature zone for 60 min, and cool with the furnace. The cooling rate is controlled to be ≤10°C / min, and cooled to below 700°C. The performance indexes of the ceramsite are measured according to the GB / T 17431.2 standard, the strength grade is 37 MPa, the bulk density is 893 kg / m 3 , and the specific strength is 41 MPa / (g / cm 3 ).

[0024] Example 2

[0025] Using a flotation tailing from Hunan and a de-alkalized red mud from Shandong as the main raw materials (the SiO₂ content in the tailing is 69%, the Al₂O₃ content is 12%, the Fe₂O₃ content is 4%, and the balance is other components; the SiO₂ content in the de-alkalized red mud is 24%, the Al₂O₃ content is 22%, the Fe₂O₃ content is 43%, and the balance is other components such as organic matter), the mixed raw material is formulated according to the SiO₂ content of 40%, the sum of the Al₂O₃ + Fe₂O₃ content of 51%, and the CaO content of 3%. After batching, it is dried, ground to less than 150 mesh and mixed evenly. The mixed material is granulated by a disk granulator to obtain green balls. The green balls are sintered: the heating rate = 12°C / min, it is necessary to hold for 3 h in the 450°C range, and control the reducing atmosphere at temperatures above 400°C so that p(O₂) = 0.01 atm. Hold at 1250°C for 120 min in the high-temperature zone and cool with the furnace, and control the cooling rate ≤ 10°C / min during cooling and cool to below 700°C. The performance indicators of the ceramsite are measured according to the GB / T 17431.2 standard, the strength grade is 40 MPa, and the bulk density is 852 kg / m 3 , and the specific strength is 47 MPa / (g / cm 3 ).

[0026] Example 3

[0027] Using a de-alkalized red mud from Guangxi and a fly ash from Shanxi as the main raw materials (the SiO₂ content in the de-alkalized red mud is 21%, the Al₂O₃ content is 25%, the Fe₂O₃ content is 38%, and the balance is other components such as organic matter; the SiO₂ content in the fly ash is 56%, the Al₂O₃ content is 28%, the Fe₂O₃ content is 7%, and the balance is other components), the mixed raw material is formulated according to the SiO₂ content of 45%, the total content of Al₂O₃ + Fe₂O₃ of 48%, and the CaO content of 2%. After batching, it is dried, ground to less than 150 mesh and mixed evenly. The mixed material is granulated by a disk granulator to obtain green balls. The green balls are sintered: the heating rate = 10°C / min, it is necessary to hold for 1 h in the 450°C range, and control the reducing atmosphere so that p(O₂) = 0.05 atm. Hold at 1250°C for 90 min in the high-temperature zone and cool with the furnace, and control the cooling rate ≤ 10°C / min during cooling and cool to below 700°C. The performance indicators of the ceramsite are measured according to the GB / T 17431.2 standard, the strength grade is 39 MPa, and the bulk density is 867 kg / m 3 , and the specific strength is 45 MPa / (g / cm 3 ).

[0028] Comparative Example 1

[0029] Other conditions are the same as in Example 1, except that the SiO2 content in the raw materials is 65%, the total content of Al2O3 + Fe2O3 is 29%, the CaO content is 5%, and the specific strength is 33 MPa / (g / cm 3 ).

[0030] Comparative Example 2

[0031] Other conditions are the same as in Example 1, except that the heating rate in the low-temperature zone below 400 °C is changed to 25 °C / min, and the specific strength is 31 MPa / (g / cm 3 ). The rapid release of low-temperature volatile gases such as H2O causes uneven pores or internal structural defects, resulting in a decrease in the specific strength of the ceramsite.

[0032] Comparative Example 3

[0033] Other conditions are the same as in Example 1, except that the cooling method is changed to natural cooling in the air, and the specific strength is 24 MPa / (g / cm 3 ). The temperature difference between the inside and outside of the ceramsite is too large, and the internal and external structures shrink unevenly, creating structural defects such as cracks, thereby reducing the specific strength of the ceramsite.

Claims

1. A preparation method of high specific strength low-silica solid waste ceramsite, characterized in that: The raw materials including metallurgical solid waste are dried, ground, mixed and granulated to obtain green pellets of ceramsite, and the green pellets of ceramsite are sintered to obtain solid waste ceramsite; The main components in the raw materials satisfy: 35wt% ≤ SiO2 content ≤ 45wt%, 45wt% ≤ Al2O3 + Fe2O3 content ≤ 55wt%, 3wt% ≤ CaO content ≤ 5wt%; The sintering system satisfies: heating and sintering at a heating rate of 8 - 15 °C / min, holding for 1 - 3 hours at 400 - 500 °C, then holding for 50 - 100 min at 1200 - 1300 °C, and then cooling; among them, when the temperature rises above 400 °C, the sintering is carried out in a reducing atmosphere; p(O2) ≤ 0.1 atm in the reducing atmosphere; The cooling is carried out by furnace cooling, controlling the cooling rate ≤ 10 °C / min and cooling to below 700 °C.

2. The preparation method of a high specific strength low-silica solid waste ceramsite according to claim 1, characterized in that: The metallurgical solid waste includes at least one of tailings, red mud, fly ash, slime, coal gangue, and steel slag.

3. The preparation method of a high specific strength low-silica solid waste ceramsite according to any one of claims 1 to 2, characterized in that: The metallurgical solid waste is ground to a particle size below 150 mesh.

4. The preparation method of a high specific strength low-silica solid waste ceramsite according to claim 1, characterized in that: The reducing atmosphere is provided by carbon, biomass or CO gas.

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