Modified bauxite tailing-based low-carbon cement and preparation method thereof

Abstract

The invention belongs to the technical field of building materials, and relates to modified bauxite tailing-based low-carbon cement and a preparation method thereof, the modified bauxite tailing-based low-carbon cement comprises the following components: 55% of Portland cement, 30% of modified bauxite tailings, and 15% of limestone powder; the modified bauxite tailings are prepared by uniformly mixing 95% of bauxite tailings and 5-85% of sodium-based desulfurization ash according to the mass ratio of 95%: 5-85%: 15% and co-calcining at 600-700 DEG C. According to the method, the content of amorphous components in the bauxite tailings is increased, the polymerization degree is modified, the early hydration rate of the bauxite tailings is increased, and part of sodium-based desulfurization ash can promote early hydration, so that the early compression resistance of the low-carbon cement is remarkably improved.

Description

Technical Field

[0001] The invention belongs to the technical field of building materials, and particularly relates to a modified bauxite tailings-based low-carbon cement and a preparation method thereof. Background Art

[0002] As global concerns about climate change and environmental degradation grow, the cement industry has to respond to the pressure to reduce huge energy consumption and greenhouse gas emissions. As one of the main sources of emissions in the industrial sector, cement production accounts for a significant proportion of carbon dioxide emissions, and its impact on the environment and human health cannot be ignored. In this context, calcined clay limestone cements (LC 3 )) has emerged as a low-carbon alternative, becoming an important tool for combating climate change due to its ability to significantly reduce carbon dioxide emissions while maintaining excellent strength and durability. However, traditional LC 3 The preparation and application of cement still faces several challenges, especially the reliance on high-cost and limited resources of metakaolin. Therefore, addressing these challenges and optimizing LC 3 The performance and production process of cement are of key significance to achieving sustainable development of the cement industry.

[0003] In preparative LC 3 In the cement production process, the use of kaolin as an alternative raw material has attracted widespread attention, which not only reduces the dependence on high-grade resources, but also provides a cost-effective solution. Bauxite tailings is a type of coal mine waste, and its main chemical component is SiO 2 and Al 2 O 3 , the main mineral phase is kaolinite. In this case, if bauxite tailings are incorporated as a metakaolin substitute, it can not only reduce costs but also show certain potential activity in the mixture. However, this approach may also be accompanied by challenges, especially when the kaolinite content is low, which will weaken the pozzolanic reaction and the overall strength of concrete, especially the early compressive strength. Summary of the invention

[0004] The purpose of the present invention is to provide a modified bauxite tailings-based low-carbon cement and a preparation method thereof, which can not only reduce LC 3 The reliance on high-grade raw materials can also increase LC 3 It can not only improve the early compressive strength, but also complete the application of bauxite tailings in building materials, promoting the green and sustainable development of building materials.

[0005] The technical solution adopted by the present invention is as follows: The present invention provides a modified bauxite tailings-based low-carbon cement and a preparation method thereof, which is composed of the following components: 55% of silicate cement, 30% of modified bauxite tailings, and 15% of limestone powder; the preparation method of the modified bauxite tailings is as follows: (1) After the bauxite tailings are dried at 105 degrees for 24 hours, they are sieved through a 20-mesh sieve and set aside; (2) After the sodium-based desulfurization ash is dried at 105 degrees for 24 hours, it is passed through a 20-mesh sieve and set aside; (3) The materials treated in steps (1) and (2) were mixed in a mass ratio of bauxite tailings: sodium-based desulfurization ash = 95%: 5~85%: 15%, and then ground in a ball mill for 5 minutes at a speed of 350 rpm. (4) placing the powder obtained in step (3) into a muffle furnace and calcining it at a heating rate of 10 degrees / min, a calcination temperature of 600-700 degrees, and a calcination time of 1-3 hours to obtain modified bauxite tailings; The bauxite tailings contain 0.25% sodium oxide, 44.3% aluminum oxide, 36.5% silicon dioxide and 1.24% potassium oxide.

[0006] The sodium-based desulfurization ash contains 47.91% sodium oxide and 46.62% sulfur trioxide, and its mineral composition is sodium sulfate.

[0007] The chemical composition of the limestone powder is 93.71% calcium oxide, 2.29% silicon dioxide, and 2.01% magnesium oxide, and the mineral composition is calcium carbonate.

[0008] The grade of the Portland cement is 42.5.

[0009] The following steps are involved: Step 1: Add 55% of Portland cement, 30% of modified bauxite tailings, and 15% of limestone powder into a mixer in sequence according to the proportions, and stir for 2 minutes; Step 2: Add water into the blender according to the ratio and stir for 2 minutes; Step 3: Pour the evenly stirred slurry mixture into the mold and perform standard curing for 3 days to complete the preparation.

[0010] Beneficial effects of the present invention: In low carbon cement LC 3The key to determining the effect of kaolin, a silicon-aluminum phase raw material, on its performance in the system is the reactivity of the silicon-aluminum phase material. Using low-grade silicon-aluminum phase raw material bauxite tailings as a replacement will inevitably lead to a slowdown in the dissolution rate of silicon and aluminum, which in turn leads to a decrease in the early compressive properties of low-carbon cement. To this end, this study used sodium-based desulfurization ash and bauxite tailings to co-calcine at 600-700 degrees. On the one hand, it can increase the active components of bauxite tailings. On the other hand, between 600-700 degrees, the effective component sodium sulfate in the sodium-based desulfurization ash will be partially decomposed into NaO, Na + It can be used as a network modifier ion of the silicate structure, changing the structure of the silicate, further increasing the active components while increasing the number of non-bridging oxygen in the amorphous components. Furthermore, the remaining sodium sulfate can be used as an early strength component of cement to promote the hydration of cement, which makes the early strength of modified bauxite tail-based low-carbon cement better than that of silicate cement. DETAILED DESCRIPTION

[0011] The following is further described in conjunction with specific embodiments, but the specific embodiments below should not be understood as limiting the present invention. Various changes and modifications that can be made by ordinary technicians in this field based on the present invention should all be within the scope of the invention.

[0012] Comparative Example 1: Raw material preparation: Portland cement 100%; Step 1: Add 100% of Portland cement into the mixer according to the proportion and stir for 2 minutes; Step 2: Add water to the mixer according to the ratio and stir for 2 minutes. The water-to-binder ratio is fixed at 0.5; Step 3: Pour the evenly stirred slurry mixture into the mold, standard cure for 3 days, complete the preparation, and test its compressive strength.

[0013] Comparative Example 2: Raw material preparation: Portland cement 55%, bauxite tailings 30%, limestone powder 15%; (1) After the bauxite tailings are dried at 105 degrees for 24 hours, they are sieved through a 20-mesh sieve and set aside; (2) placing the powder obtained in step (1) into a muffle furnace and calcining it at a heating rate of 10 degrees / min, a calcination temperature of 600 degrees, and a calcination time of 3 hours to obtain calcined bauxite tailings; Specimen preparation: Step 1: Add 55% of Portland cement, 30% of calcined bauxite tailings, and 15% of limestone powder into a mixer in sequence according to the proportions, and stir for 2 minutes; Step 2: Add water to the mixer according to the ratio and stir for 2 minutes. The water-to-binder ratio is fixed at 0.5; Step 3: Pour the evenly stirred slurry mixture into the mold, standard cure for 3 days, complete the preparation, and test its compressive strength.

[0014] Comparative Example 3: Raw material preparation: Portland cement 55%, bauxite tailings 27%, sodium-based desulfurization ash 3%, limestone powder 15%; (1) After the bauxite tailings are dried at 105 degrees for 24 hours, they are sieved through a 20-mesh sieve and set aside; (2) placing the powder obtained in step (1) into a muffle furnace and calcining it at a heating rate of 10 degrees / min, a calcination temperature of 600 degrees, and a calcination time of 3 hours to obtain calcined bauxite tailings; Specimen preparation: Step 1: Add 55% of silicate cement, 27% of bauxite tailings, 3% of sodium-based desulfurization ash, and 15% of limestone powder into the mixer in sequence according to the proportion, and stir for 2 minutes; Step 2: Add water to the mixer according to the ratio and stir for 2 minutes. The water-to-binder ratio is fixed at 0.5; Step 3: Pour the evenly stirred slurry mixture into the mold, standard cure for 3 days, complete the preparation, and test its compressive strength. Example

[0015] Raw material preparation: Portland cement 55%, modified bauxite tailings 30%, limestone powder 15% (1) After the bauxite tailings are dried at 105 degrees for 24 hours, they are sieved through a 20-mesh sieve and set aside; (2) After the sodium-based desulfurization ash is dried at 105 degrees for 24 hours, it is passed through a 20-mesh sieve and set aside; (3) The materials treated in steps (1) and (2) were mixed in a mass ratio of bauxite tailings: sodium-based desulfurization ash = 90%: 10%, and then ground in a ball mill for 5 minutes at a speed of 350 rpm. (4) placing the powder obtained in step (3) into a muffle furnace and calcining the powder at a heating rate of 10 degrees / min, a calcination temperature of 600 degrees, and a calcination time of 3 hours to obtain modified bauxite tailings; Specimen preparation: Step 1: Add 55% of Portland cement, 30% of modified bauxite tailings, and 15% of limestone powder into a mixer in sequence according to the proportions, and stir for 2 minutes; Step 2: Add water into the blender according to the ratio and stir for 2 minutes; Step 3: Pour the evenly stirred slurry mixture into the mold and perform standard curing for 3 days to complete the preparation. Example

[0016] Raw material preparation: Portland cement 55%, modified bauxite tailings 30%, limestone powder 15% (1) After the bauxite tailings are dried at 105 degrees for 24 hours, they are sieved through a 20-mesh sieve and set aside; (2) After the sodium-based desulfurization ash is dried at 105 degrees for 24 hours, it is passed through a 20-mesh sieve and set aside; (3) The materials treated in steps (1) and (2) were mixed in a mass ratio of bauxite tailings: sodium-based desulfurization ash = 95%:5%, and then ground in a ball mill for 5 minutes at a speed of 350 rpm. (4) placing the powder obtained in step (3) into a muffle furnace and calcining the powder at a heating rate of 10 degrees / min, a calcination temperature of 700 degrees, and a calcination time of 3 hours to obtain modified bauxite tailings; Specimen preparation: Step 1: Add 55% of Portland cement, 30% of modified bauxite tailings, and 15% of limestone powder into a mixer in sequence according to the proportions, and stir for 2 minutes; Step 2: Add water into the blender according to the ratio and stir for 2 minutes; Step 3: Pour the evenly stirred slurry mixture into the mold and perform standard curing for 3 days to complete the preparation. Example

[0017] Raw material preparation: Portland cement 55%, modified bauxite tailings 30%, limestone powder 15% (1) After the bauxite tailings are dried at 105 degrees for 24 hours, they are sieved through a 20-mesh sieve and set aside; (2) After the sodium-based desulfurization ash is dried at 105 degrees for 24 hours, it is passed through a 20-mesh sieve and set aside; (3) The materials treated in steps (1) and (2) were mixed in a mass ratio of bauxite tailings: sodium-based desulfurization ash = 90%: 10%, and then ground in a ball mill for 5 minutes at a speed of 350 rpm. (4) placing the powder obtained in step (3) into a muffle furnace and calcining the powder at a heating rate of 10 degrees / min, a calcination temperature of 700 degrees, and a calcination time of 3 hours to obtain modified bauxite tailings; Specimen preparation: Step 1: Add 55% of Portland cement, 30% of modified bauxite tailings, and 15% of limestone powder into a mixer in sequence according to the proportions, and stir for 2 minutes; Step 2: Add water into the blender according to the ratio and stir for 2 minutes; Step 3: Pour the evenly stirred slurry mixture into the mold and perform standard curing for 3 days to complete the preparation. Example

[0018] Raw material preparation: Portland cement 55%, modified bauxite tailings 30%, limestone powder 15% (1) After the bauxite tailings are dried at 105 degrees for 24 hours, they are sieved through a 20-mesh sieve and set aside; (2) After the sodium-based desulfurization ash is dried at 105 degrees for 24 hours, it is passed through a 20-mesh sieve and set aside; (3) The materials treated in steps (1) and (2) were mixed in a mass ratio of bauxite tailings: sodium-based desulfurization ash = 85%: 15%, and then ground in a ball mill for 5 minutes at a speed of 350 rpm. (4) placing the powder obtained in step (3) into a muffle furnace and calcining the powder at a heating rate of 10 degrees / min, a calcination temperature of 700 degrees, and a calcination time of 3 hours to obtain modified bauxite tailings; Specimen preparation: Step 1: Add 55% of Portland cement, 30% of modified bauxite tailings, and 15% of limestone powder into a mixer in sequence according to the proportions, and stir for 2 minutes; Step 2: Add water into the blender according to the ratio and stir for 2 minutes; Step 3: Pour the evenly stirred slurry mixture into the mold and perform standard curing for 3 days to complete the preparation.

[0019] Performance Testing: The early compressive strength of the cement paste obtained in Examples 1 to 4 and Comparative Examples 1 to 2 was tested, and the test results were as follows: Grouping Comparative Example 1 Comparative Example 2 Comparative Example 3 Example 1 Example 2 Example 3 Example 4 3-day compressive strength / MPa 18.1 14.3 17.5 29.6 28.8 28.6 26.5 By comparing Examples 1 to 4 with Comparative Examples 1 to 3, it can be found that the co-calcination of sodium-based desulfurization ash and bauxite tailings between 600 and 700 degrees significantly improves the early compressive resistance of low carbon cement.

[0020] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A modified bauxite tailings-based low-carbon cement, characterized in that: It is composed of the following components: 55% silicate cement, 30% modified bauxite tailings, and 15% limestone powder.

2. The modified bauxite tailings-based low-carbon cement according to claim 1, characterized in that: The modified bauxite tailings contain 0.25% sodium oxide, 44.3% aluminum oxide, 36.5% silicon dioxide and 1.24% potassium oxide.

3. The modified bauxite tailings-based low-carbon cement according to claim 1, characterized in that: The chemical composition of the limestone powder is 93.71% calcium oxide, 2.29% silicon dioxide, and 2.01% magnesium oxide, and the mineral composition is calcium carbonate.

4. The modified bauxite tailings-based low-carbon cement according to claim 1, characterized in that: The grade of Portland cement is 42.

5.

5. A method for preparing a modified bauxite tailings-based low-carbon cement according to any one of claims 1 to 4, characterized in that: The following steps are involved: Step 1: Add 55% of Portland cement, 30% of modified bauxite tailings, and 15% of limestone powder into a mixer in sequence according to the proportions, and stir for 2 minutes; Step 2: Add water into the blender according to the ratio and stir for 2 minutes; Step 3: Pour the evenly stirred slurry mixture into the mold and perform standard curing for 3 days to complete the preparation.

6. The method for preparing a modified bauxite tailings-based low-carbon cement according to claim 5, characterized in that: The modified bauxite tailings preparation method is: (1) After the bauxite tailings are dried at 105 degrees for 24 hours, they are sieved through a 20-mesh sieve and set aside; (2) After the sodium-based desulfurization ash is dried at 105 degrees for 24 hours, it is passed through a 20-mesh sieve and set aside; (3) The materials treated in steps (1) and (2) were mixed in a mass ratio of bauxite tailings: sodium-based desulfurization ash = 95%: 5-85%: 15%, and ground in a ball mill for 5 min at a speed of 350 rpm; (4) The powder obtained in step (3) is placed in a muffle furnace and calcined at a heating rate of 10 degrees / min, a calcination temperature of 600-700 degrees, and a calcination time of 1-3 hours to obtain modified bauxite tailings.

7. The modified bauxite tailings-based low-carbon cement according to claim 6, characterized in that: The sodium-based desulfurization ash contains 47.91% sodium oxide and 46.62% sulfur trioxide, and its mineral composition is sodium sulfate.