Low-calcium clinker and preparation method thereof

Abstract

The invention relates to the technical field of cement-based building materials, in particular to a low-calcium clinker and a preparation method thereof.The low-calcium clinker is prepared by conducting dealkalization treatment on red mud to obtain dealkalized red mud, preparing raw materials from the dealkalized red mud, carbide slag, fly ash and coal gangue and then conducting calcination to prepare the low-calcium clinker, and meanwhile high-grade recycling of regenerated iron can be achieved.

Description

Technical Field

[0001] The invention relates to the technical field of cement-based building materials, in particular to a low-calcium clinker and a preparation method thereof. Background Art

[0002] Red mud is an industrial solid waste discharged when the aluminum industry extracts alumina. For every ton of alumina produced, 1.0-1.8 tons of red mud are discharged. The storage of red mud not only occupies a large amount of land resources, but also pollutes the soil and water around the storage yard. It can easily cause dam breaches under severe climatic conditions, seriously affecting the lives of surrounding residents.

[0003] According to the different production methods of alumina, red mud is divided into Bayer red mud and sintering red mud. Currently, 90% of the red mud on the market is Bayer red mud. The iron content of Bayer red mud is very high, usually 30-60%. According to its high-speed rail characteristics, a large number of scholars have conducted research on the recovery of iron from Bayer red mud. For example, the prior art CN118726684A discloses a red mud iron extraction method based on arc furnace hydrogen plasma melting reduction technology, and the Chinese invention patent application CN118291750A discloses a red mud high-efficiency gravity-magnetic combined iron extraction process. The Chinese invention patent application CN118563097A discloses a high-speed iron red mud dealkalization resource utilization process and its application. In the prior art, a high-temperature environment is often used in the process of recovering iron from red mud. Due to the strong alkalinity of red mud, it will cause the blast furnace to crust, and blast furnace ironmaking still has problems such as energy consumption and high carbon emissions.

[0004] Low-calcium clinker has a low calcium content and requires less calcium raw materials, which can reduce carbon emissions caused by carbonate calcination. It has become a research hotspot in recent years. Its low calcium content also makes the firing temperature of low-calcium clinker low, further reducing fuel consumption and CO2 emissions. In addition, low-calcium clinker has the characteristics of low hydration activity and high carbonization activity. In the process of carbonization hardening to obtain excellent mechanical properties, it can achieve CO2 sequestration, which has significant environmental benefits. Summary of the invention

[0005] In order to solve the problems existing in the prior art, the present invention provides a low-calcium clinker, which is obtained by dealkalizing red mud, preparing raw material with carbide slag, fly ash and coal gangue as raw materials, and then calcining to prepare low-calcium clinker, while achieving high-grade recovery of regenerated iron.

[0006] Specifically, the method for preparing low-calcium clinker of the present invention comprises the following steps: 1) Mix red mud and carbide slag, add water to form a suspension, perform hydrothermal reaction, wash, filter, dry and grind to obtain dealkalized red mud. 2) Weigh 40-60 parts of dealkalized red mud, 20-30 parts of carbide slag, 20-30 parts of fly ash, and 1-3 parts of coal gangue by weight, mix them evenly, and grind them to obtain raw material. 3) The raw material is calcined, cooled, crushed and magnetically separated to obtain recycled iron, and the remaining material is ground into low-calcium clinker.

[0007] During the high-temperature iron extraction process of red mud, high-temperature treatment will stimulate the potential gelling activity of red mud, but its activity is low, the amount of cement replaced is limited, and the tailings from red mud iron extraction are mainly glassy phase, and the energy consumption of grinding is large. Therefore, the present invention first uses carbide slag as a dealkalizing agent before high-temperature calcination of red mud to extract iron, thereby reducing the alkalinity of red mud and improving the calcium-poor characteristics of red mud. Then, dealkalizing red mud, fly ash, carbide slag and coal gangue are used to prepare raw materials. Coal gangue is used as a reducing agent at high temperature and also as raw material to provide oxides to prepare low-calcium clinker. Magnetic separation is used to separate the regenerated iron from the clinker. The obtained regenerated iron has high grade. The low-calcium clinker can absorb CO2 during curing to achieve carbon sequestration.

[0008] Preferably, in step 1), the mass ratio of red mud to carbide slag is 1:(0.2-0.5).

[0009] Preferably, in step 1), the liquid-to-solid ratio of the suspension is (2-6):1.

[0010] Preferably, in step 1), the hydrothermal reaction temperature is 70-90° C., the stirring speed is 300-600 rpm, and the reaction time is 2-6 h.

[0011] Preferably, the main chemical components of the dealkalized red mud in step 1) are CaO: 30-35%, Fe2O3: 20-30%, Al2O3: 8-12%, SiO2: 3-6%, and TiO2: 1-3%.

[0012] Preferably, the main chemical components of the carbide slag in step 2) are: CaO: 65-70%, SiO2: 3-6%, Al2O3: 0-2%.

[0013] Preferably, the main chemical components of the fly ash in step 2) are: CaO: 0-5%, SiO2: 40-50%, Al2O3: 30-45%.

[0014] Preferably, the main chemical components of the coal gangue in step 2) are: C: 40-60%, SiO2: 10-20%, Al2O3: 10-20%, CaO: 10-20%, SO3: 10-20%.

[0015] Preferably, the raw material particle size in step 2) is less than 200 μm.

[0016] Preferably, in step 3), the calcination temperature is 1250-1350° C. and the calcination time is 2-3 h.

[0017] Preferably, the grade of the recycled iron in step 3) is 70-87.8%.

[0018] Preferably, in step 3), the particle size of the low calcium clinker is less than 75 μm.

[0019] The present invention also relates to low-calcium clinker, which is specifically prepared by the above-mentioned preparation method.

[0020] Preferably, the γ-C2S content in the low-calcium clinker is 30-68%, and the β-C2S content is 17-26%. Studies have shown that the clinker of the present invention is mainly composed of γ-C2S and β-C2S, and contains some C2AS and C 12 Mineral phases such as A7 are low-calcium clinkers that can achieve carbon sequestration and are also low-carbon clinkers.

[0021] The present invention has the following technical advantages: 1. The present invention adjusts the element composition of red mud by dealkalization, thereby improving the recycling rate of red mud; 2. The present invention uses carbide slag as a dealkalizing agent, which not only effectively dealkalizes and ensures that the kiln will not form a crust when the red mud is treated at high temperature, but also increases the calcium and silicon content in the red mud, making it easier to burn the clinker. 3. The present invention uses all solid waste to prepare low-calcium clinker and simultaneously co-produces high-grade recycled iron. The low-calcium clinker can achieve carbon sequestration, which is waste-recycling and environmentally friendly. DETAILED DESCRIPTION

[0022] In order to characterize the technical effect of the present invention, clinker was prepared and its performance was tested. During the test, the grade of the regenerated iron was determined by potassium dichromate titration. For the mineral composition of the clinker, the mineral composition of the clinker was quantitatively analyzed by XRD structure refinement using Highscore Plus software. After the clinker was prepared, the clinker and water were mixed evenly at a water-binder ratio of 0.1. The sample was formed into a cylinder with a diameter of 20 mm and a height of 20 mm by pressing and molding. The molding pressure was 10 MPa. It was carbonized for 24 hours under the conditions of 75% humidity, 25°C temperature, and 0.2 MPa CO2 partial pressure. The carbonization amount was calculated by mass difference. The compressive strength of the carbonized test block was tested on a universal pressure testing machine. During the preparation process, the raw material was uniformly ground to a particle size of less than 200 μm, and the clinker was uniformly ground to a particle size of less than 75 μm.

[0023] Embodiment 1, the preparation method of clinker comprises the following steps: 1) Mix red mud and carbide slag in a mass ratio of 1:0.4, add water to form a suspension, perform hydrothermal reaction at 80℃ for 4h, wash, filter, dry and grind to obtain dealkalized red mud. 2) Weigh 52 parts of dealkalized red mud, 22 parts of carbide slag, 28 parts of fly ash, and 2 parts of coal gangue by weight, mix them evenly, and grind them to obtain raw material. 3) The raw material is calcined, cooled, crushed and magnetically separated to obtain recycled iron, and the remaining material is ground into clinker.

[0024] After testing, the grade of recycled iron is 81.6%, the content of γ-C2S in clinker mineral is 65.1%, the content of β-C2S is 19.8%, the 24h compressive strength is 168.4MPa, and the carbon fixation is 14.9%.

[0025] Embodiment 2, the preparation method of clinker comprises the following steps: 1) Mix red mud and carbide slag in a mass ratio of 1:0.5, add water to form a suspension, perform hydrothermal reaction at 80℃ for 4h, wash, filter, dry and grind to obtain dealkalized red mud. 2) Weigh 50 parts of dealkalized red mud, 28 parts of carbide slag, 25 parts of fly ash, and 3 parts of coal gangue by weight, mix them evenly, and grind them to obtain raw material. 3) The raw material is calcined, cooled, crushed and magnetically separated to obtain recycled iron, and the remaining material is ground into clinker.

[0026] After testing, the grade of recycled iron is 85.8%, the content of γ-C2S in clinker mineral is 63.4%, the content of β-C2S is 23.6%, the 24h compressive strength is 157.2MPa, and the carbon fixation is 15.3%.

[0027] Comparative Example 1, a method for preparing clinker, comprising the following steps: 1) Weigh 52 parts of red mud, 22 parts of carbide slag, 28 parts of fly ash and 2 parts of coal gangue by weight, mix them evenly and grind them to obtain raw material. 2) The raw material is calcined, cooled, crushed and magnetically separated to obtain recycled iron, and the remaining material is ground into clinker.

[0028] After testing, the grade of recycled iron is 34.6%, the content of γ-C2S in clinker mineral is 28.7%, the content of β-C2S is 6.5%, the 24h compressive strength is 73.4MPa, and the carbon fixation is 5.5%.

[0029] Comparative Example 2, a method for preparing clinker, comprising the following steps: 1) Mix red mud and sulfuric acid slag in a mass ratio of 1:0.4, add water to form a suspension, perform hydrothermal reaction at 80℃ for 4h, wash, filter, dry and grind to obtain dealkalized red mud. 2) Weigh 52 parts of dealkalized red mud, 22 parts of carbide slag, 28 parts of fly ash, and 2 parts of coal gangue by weight, mix them evenly, and grind them to obtain raw material. 3) The raw material is calcined, cooled, crushed and magnetically separated to obtain recycled iron, and the remaining material is ground into clinker.

[0030] After testing, the grade of recycled iron was 46.0%, the content of γ-C2S in clinker mineral was 36.7%, the content of β-C2S was 12.4%, the 24h compressive strength was 96.5MPa, and the carbon fixation was 6.8%.

[0031] Comparative Example 3, a method for preparing clinker, comprising the following steps: 1) Mix red mud and activated calcium oxide in a mass ratio of 1:0.4, add water to form a suspension, perform hydrothermal reaction at 80℃ for 4h, wash, filter, dry and grind to obtain dealkalized red mud. 2) Weigh 52 parts of dealkalized red mud, 22 parts of carbide slag, 28 parts of fly ash, and 2 parts of coal gangue by weight, mix them evenly, and grind them to obtain raw material. 3) The raw material is calcined, cooled, crushed and magnetically separated to obtain recycled iron, and the remaining material is ground into clinker.

[0032] After testing, the grade of recycled iron is 43.6%, the content of γ-C2S in clinker mineral is 37.3%, the content of β-C2S is 7.2%, the 24h compressive strength is 89.7MPa, and the carbon fixation is 6.5%.

[0033] Comparative Example 4, a method for preparing clinker, comprising the following steps: 1) Mix red mud and carbide slag in a mass ratio of 1:0.4, add water to form a suspension, perform hydrothermal reaction at 80℃ for 4h, wash, filter, dry and grind to obtain dealkalized red mud. 2) Weigh 52 parts of dealkalized red mud, 22 parts of alkali residue, 28 parts of fly ash and 2 parts of coal gangue by weight, mix them evenly and grind them to obtain raw material. 3) The raw material is calcined, cooled, crushed and magnetically separated to obtain recycled iron, and the remaining material is ground into clinker.

[0034] After testing, the grade of recycled iron is 56.5%, the content of γ-C2S in clinker mineral is 43.2%, the content of β-C2S is 23.5%, the 24h compressive strength is 107.9MPa, and the carbon fixation is 7.7%.

[0035] Comparative Example 5, a method for preparing clinker, comprising the following steps: 1) Mix red mud and carbide slag in a mass ratio of 1:0.4, add water to form a suspension, perform hydrothermal reaction at 80℃ for 4h, wash, filter, dry and grind to obtain dealkalized red mud. 2) Weigh 52 parts of dealkalized red mud, 22 parts of carbide slag, 28 parts of fly ash, and 2 parts of activated carbon by weight, mix them evenly, and grind them to obtain raw material. 3) The raw material is calcined, cooled, crushed and magnetically separated to obtain recycled iron, and the remaining material is ground into clinker.

[0036] After testing, the grade of recycled iron is 43.4%, the content of γ-C2S in clinker mineral is 57.2%, the content of β-C2S is 15.3%, the 24h compressive strength is 124.2MPa, and the carbon fixation is 10.3%.

[0037] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing low-calcium clinker, characterized in that: The steps include: 1) Mix red mud and carbide slag, add water to form a suspension, perform hydrothermal reaction, wash, filter, dry, and grind to obtain dealkalized red mud, with a liquid-to-solid ratio of the suspension of (2-6):1; the hydrothermal reaction temperature is 70-90°C, the stirring speed is 300-600rpm, and the reaction time is 2-6h; 2) Weigh 40-60 parts of dealkalized red mud, 20-30 parts of carbide slag, 20-30 parts of fly ash, and 1-3 parts of coal gangue by weight, mix them evenly, and grind them to obtain raw material; the main chemical components of the dealkalized red mud are CaO: 30-35%, Fe2O3: 20-30%, Al2O3: 8-12%, SiO2: 3-6%, and TiO2: 1-3%; 3) The raw material is calcined, cooled, crushed and magnetically separated to obtain recycled iron, and the remaining material is ground into low-calcium clinker.

2. The method for preparing low-calcium clinker according to claim 1, characterized in that: The raw material particle size in step 2) is less than 200 μm.

3. The method for preparing low-calcium clinker according to claim 1, characterized in that: In step 3), the calcination temperature is 1250-1350°C.

4. The method for preparing low-calcium clinker according to claim 1, characterized in that: The calcination time in step 3) is 2-3h.

5. The method for preparing low-calcium clinker according to claim 1, characterized in that: In step 3), the grade of recycled iron is 70-87.8%.

6. The method for preparing low-calcium clinker according to claim 1, characterized in that: Step 3) The particle size of medium and low calcium clinker is below 75 μm.

7. Low calcium clinker, characterized in that The compound is prepared by the preparation method according to any one of claims 1 to 6.

8. The low-calcium clinker according to claim 7, characterized in that: The γ-C2S content in the low-calcium clinker is 30-68%, and the β-C2S content is 17-26%.