A method for improving the activity of bayer process red mud

Abstract

The application provides a method for improving the activity of Bayer process red mud, and comprises the following steps: S1. drying Bayer process red mud and carbide slag respectively to a water content of less than 1.0%, and grinding to obtain red mud powder and carbide slag powder; S2. mixing the red mud powder and the carbide slag powder, and calcining to obtain active mixture; wherein the mass ratio of the red mud powder and the carbide slag powder is 65-80:20-35. The method is simple, economical and environmentally friendly. By mixing the carbide slag and the red mud in a specific ratio, and calcining at high temperature, a new phase is generated by the reaction between the chemical components of the two, the activity of the Bayer process red mud is improved, and the two types of waste residues are converted into directly usable cement mixture.

Description

Technical Field

[0001] This invention belongs to the field of cement manufacturing technology, specifically relating to a method for improving the activity of Bayer process red mud. Background Technology

[0002] my country is the largest producer of alumina, requiring the import of large quantities of bauxite annually. In 2024, China imported 159 million tons of bauxite, of which 110 million tons (69.18%) came from Guinea. The red mud discharged from this bauxite after alumina production via the Bayer process is known as Guinean Bayer process red mud. Currently, red mud is mainly used for metal recycling, as a corrective material for iron in cement clinker production, and road construction; however, the comprehensive utilization rate of this red mud resource is only 14%. In December 2024, six departments, including the Ministry of Industry and Information Technology, jointly issued the "Action Plan for Comprehensive Utilization of Red Mud," proposing that by 2027, positive progress should be made in the comprehensive utilization of red mud, with the newly added red mud comprehensive utilization rate reaching 15%; and by 2030, the level of comprehensive utilization of red mud should be further improved, with the newly added red mud comprehensive utilization rate reaching 25%. This indicates that the comprehensive utilization of red mud resources faces significant challenges.

[0003] Calcium carbide slag is an industrial waste residue formed during the industrial production of acetylene, polyvinyl chloride, and polyvinyl alcohol by the hydrolysis of calcium carbide (CaC2). Its main component is Ca(OH)2, and it also contains oxides such as SiO2, Al2O3, and Fe2O3, as well as small amounts of organic matter. Its CaO content is over 60%, and it is characterized by strong alkalinity and difficulty in disposal. Tens of millions of tons of calcium carbide slag are discharged into my country annually. Direct discharge not only occupies land but also pollutes water resources, and after drying, it causes dust and air pollution.

[0004] In the power industry, with the significant increase in installed capacity of green power such as photovoltaic, wind power, and nuclear power, the amount of coal-fired power generation will inevitably decrease gradually. At that time, high-quality mixed materials such as fly ash and slag required for cement grinding may face a shortage.

[0005] Using the vast reserves of Guinea's Bayer process red mud as a blending material in cement grinding would play a significant role in the comprehensive utilization of red mud resources. This would not only solve the environmental pollution problem caused by long-term red mud stockpiling but also provide a high-quality blending material for cement production. However, directly using red mud in cement grinding presents the following problems: 1. High moisture content (around 30%); 2. Complex composition and unstable properties; 3. High loss on ignition; 4. Low activity. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a method for improving the activity of Bayer process red mud. This method is simple, economical, and environmentally friendly, requiring no chemical additives or pre-treatment of the red mud for dealkalization. By mixing carbide slag and red mud in a specific ratio and then calcining them at high temperatures, a new phase is generated through the reaction between their chemical components, thereby improving the activity of the Bayer process red mud and converting both types of waste slag into a directly usable cementitious admixture.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A first aspect of the present invention provides a method for improving the activity of Bayer process red mud, comprising the following steps: S1. Dry the Bayer process red mud and carbide slag separately until the moisture content is less than 1.0%, then grind them to obtain red mud powder and carbide slag powder; S2. Mix the red mud powder with the carbide slag powder and calcine to obtain an active mixture; The mass ratio of the red mud powder to the calcium carbide slag powder is 65-80:20-35; The chemical composition of the active mixture includes CaO, Ca2Fe2O5, C2S, C3A, and Fe2O3.

[0009] Furthermore, the Bayer process red mud contains 5.0% water of crystallization.

[0010] Further, in step S1, the drying includes drying Bayer red mud in a drying oven at 200°C and drying carbide slag in a drying oven at 105°C.

[0011] Further, in step S1, the grinding involves grinding Bayer red mud and carbide slag to a fineness of 2.5% with a particle size of 80 μm.

[0012] Further, in step S2, the specific steps for obtaining the active mixture include: The red mud powder and the calcium carbide slag powder are mixed at a mass ratio of 80:20, 75:25, 70:30 or 65:35 and calcined at 950°C for 4 hours to obtain the active mixture.

[0013] A second aspect of the present invention provides a method for evaluating the activity of an active mixture as described above, comprising the following steps: S1. Mix clinker with natural gypsum, grind, and obtain silicate cement; S2. A sample was prepared by adding 30 wt% of the active admixture to silicate cement; S3. Conduct mortar strength tests on silicate cement and samples; S4. Calculate the activity index of the reactive mixture using the following formula: A=

[0014] In the formula: A represents the activity index of the active mixture, %; The compressive strength of the sample after 28 days, in MPa; The value represents the 28-day compressive strength of silicate cement, in MPa.

[0015] Furthermore, the silicate cement is composed of 96.8 wt% clinker and 3.2 wt% natural gypsum.

[0016] Furthermore, the cooked material is homemade.

[0017] Furthermore, the mortar strength test was conducted in accordance with GB / T17671.

[0018] Furthermore, the activity index of the active mixture is ≥74.0%.

[0019] The beneficial effects of this invention are: The active mixture prepared by this invention has an activity index ≥74.0%, which meets the requirements of GB / T2842-2011 "Pozzolanic Blends for Cement" requiring an activity index ≥60% and GB / T1596 "Fly Ash for Cement and Concrete" requiring an activity index ≥70%.

[0020] This invention involves incorporating 30 wt% of carbide slag (dried at 105°C and ground to 80 μm fineness, 2.5%) into Bayer process red mud (dried at 200°C and ground to 80 μm fineness, 2.5%). After uniform mixing, the mixture is calcined at 950°C for 4 hours to obtain an active mixture with an activity index of 81.8%, which is 18.9% higher than that of red mud without carbide slag. During the high-temperature calcination process, components in the carbide slag participate in the reaction, generating new phases such as CaO, Ca2Fe2O5, C2S, and C3A in the active mixture. The incorporation of carbide slag alters the phase composition of the red mud. Attached Figure Description

[0021] Figure 1 The images show the XRD patterns of the active mixtures prepared in Examples 1-4 and Comparative Examples 1-4 of this invention. Detailed Implementation

[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0023] A method for improving the activity of Bayer process red mud includes the following steps: Bayer process red mud and carbide slag are dried to a moisture content of less than 1.0% and then ground to obtain red mud powder and carbide slag powder. The red mud powder and the calcium carbide slag powder are mixed and calcined to obtain an active mixture. The mass ratio of the red mud powder to the calcium carbide slag powder is 65-80:20-35.

[0024] In some embodiments, the Bayer red mud contains 5.0% water of crystallization.

[0025] In some embodiments, the drying includes drying Bayer red mud in a drying oven at 200°C and drying calcium carbide slag in a drying oven at 105°C.

[0026] In some embodiments, the grinding involves grinding Bayer red mud and carbide slag to a fineness of 2.5% of 80 μm.

[0027] In some embodiments, the specific steps for obtaining the active mixture include: The red mud powder and the calcium carbide slag powder are mixed at a mass ratio of 80:20, 75:25, 70:30 or 65:35 and calcined at 950°C for 4 hours to obtain the active mixture.

[0028] In some embodiments, red mud powder is designated as "R" and calcium carbide slag powder is designated as "C".

[0029] In some embodiments, red mud powder and carbide slag powder are mixed at a mass ratio of 80:20 and calcined at 950°C for 4 hours to obtain an active mixture designated as "R80 / C20".

[0030] In some embodiments, red mud powder and carbide slag powder are mixed at a mass ratio of 75:25 and calcined at 950°C for 4 hours to obtain an active mixture designated as "R75 / C25".

[0031] In some embodiments, red mud powder and carbide slag powder are mixed at a mass ratio of 70:30 and calcined at 950°C for 4 hours to obtain an active mixture designated as "R70 / C30".

[0032] In some embodiments, red mud powder and carbide slag powder are mixed at a mass ratio of 65:35 and calcined at 950°C for 4 hours to obtain an active mixture designated as "R65 / C35".

[0033] The present invention will be further described in detail below with reference to specific embodiments. It should be noted that the specific embodiments are explanations of the present invention and not limitations thereof.

[0034] In the following embodiments, the Bayer process red mud material originates from: Chinalco Zhengzhou Branch; the calcium carbide slag material originates from: Jiaozuo Haohua Aerospace Company; the clinker material originates from: Tianrui Zhengzhou; and the natural gypsum material originates from: Jingmen, Hubei.

[0035] Table 1. Chemical composition of Bayer process red mud, carbide slag, clinker, and natural gypsum

[0036] Bayer process red mud is the red mud discharged after the production of alumina from Guinean bauxite using the Bayer process by Chinalco Zhengzhou Branch. Its chemical composition contains SiO2, Al2O3, and Fe2O3 contents of more than 10.0%, while the CaO content is less than 1.0%; the chemical composition of carbide slag contains CaO content of more than 65.0%.

[0037] A method for evaluating the activity of an active mixture as described above includes the following steps: S1. Mix clinker with natural gypsum, grind, and obtain silicate cement; S2. A sample was prepared by adding 30 wt% of the active admixture to silicate cement; S3. Conduct mortar strength tests on silicate cement and samples; S4. Calculate the activity index of the reactive mixture using the following formula: A=

[0038] In the formula: A represents the activity index of the active mixture, %; The compressive strength of the sample after 28 days, in MPa; The value represents the 28-day compressive strength of silicate cement, in MPa.

[0039] In some embodiments, silicate cement is designated as "PI".

[0040] Table 2. Chemical composition of silicate cement

[0041] In some embodiments, the mortar strength test is performed in accordance with GB / T17671.

[0042] Example 1 Bayer process red mud was dried in a drying oven at 200℃ until the moisture content was less than 1.0%, and carbide slag was dried in a drying oven at 105℃ until the moisture content was less than 1.0%. Then, they were ground to a fineness of 2.5% of 80μm to obtain red mud powder R and carbide slag powder C. The red mud powder and carbide slag powder were mixed at a mass ratio of 80:20 and calcined at 950℃ for 4 hours to obtain active mixture R80 / C20.

[0043] According to the GB / T21372 test method for physical properties of silicate cement clinker, 3.2% natural gypsum was added to the clinker during production, utilizing a φ500mm... A 500mm standard test mill was used to grind silicate cement PI. 30wt% of active admixture R80 / C20 was added to the silicate cement PI to prepare a sample. Then, the mortar strength test was carried out on the silicate cement PI and the sample according to GB / T17671. The 28-day compressive strength of silicate cement PI was 53.4MPa, and the activity index of active admixture R80 / C20 was calculated to be 74.0%.

[0044] Example 2 Bayer process red mud was dried in a drying oven at 200℃ until the moisture content was less than 1.0%, and carbide slag was dried in a drying oven at 105℃ until the moisture content was less than 1.0%. Then, they were ground to a fineness of 2.5% (80μm) to obtain red mud powder R and carbide slag powder C. The red mud powder and carbide slag powder were mixed at a mass ratio of 75:25 and calcined at 950℃ for 4 hours to obtain active mixture R75 / C25.

[0045] According to the GB / T21372 test method for physical properties of silicate cement clinker, 3.2% natural gypsum was added to the clinker during production, utilizing a φ500mm... A 500mm standard test mill was used to grind silicate cement PI. 30wt% of active admixture R75 / C25 was added to the silicate cement PI to prepare a sample. Then, the mortar strength test was carried out on the silicate cement PI and the sample according to GB / T17671. The activity index of active admixture R75 / C25 was calculated to be 77.9%.

[0046] Example 3 Bayer process red mud was dried in a drying oven at 200℃ until the moisture content was less than 1.0%, and carbide slag was dried in a drying oven at 105℃ until the moisture content was less than 1.0%. Then, they were ground to a fineness of 2.5% (80μm) to obtain red mud powder R and carbide slag powder C. The red mud powder and carbide slag powder were mixed at a mass ratio of 70:30 and calcined at 950℃ for 4 hours to obtain active mixture R70 / C30.

[0047] According to the GB / T21372 test method for physical properties of silicate cement clinker, 3.2% natural gypsum was added to the clinker during production, utilizing a φ500mm... A 500mm standard test mill was used to grind silicate cement PI; 30wt% of active admixture R70 / C30 was added to the silicate cement PI to prepare a sample. Then, the mortar strength test was carried out on the silicate cement PI and the sample according to GB / T17671, and the activity index of active admixture R70 / C30 was calculated to be 81.8%.

[0048] Example 4 Bayer process red mud was dried in a drying oven at 200℃ until the moisture content was less than 1.0%, and carbide slag was dried in a drying oven at 105℃ until the moisture content was less than 1.0%. Then, they were ground to a fineness of 2.5% of 80μm to obtain red mud powder R and carbide slag powder C. The red mud powder and carbide slag powder were mixed at a mass ratio of 65:35 and calcined at 950℃ for 4 hours to obtain active mixture R65 / C35.

[0049] According to the GB / T21372 test method for physical properties of silicate cement clinker, 3.2% natural gypsum was added to the clinker during production, utilizing a φ500mm... A 500mm standard test mill was used to grind silicate cement PI. 30wt% of active admixture R65 / C35 was added to the silicate cement PI to prepare a sample. Then, the mortar strength test was carried out on the silicate cement PI and the sample according to GB / T17671. The activity index of active admixture R65 / C35 was calculated to be 76.0%.

[0050] Comparative Example 1 Bayer process red mud was dried in a drying oven at 200°C until the moisture content was less than 1.0%, and then ground to a fineness of 2.5% (80 μm) to obtain red mud powder R.

[0051] According to the GB / T21372 test method for physical properties of silicate cement clinker, 3.2% natural gypsum was added to the clinker during production, utilizing a φ500mm... A 500mm standard test mill was used to grind silicate cement PI; 30wt% red mud powder R was added to the silicate cement PI to prepare a sample. Then, the mortar strength test was carried out on the silicate cement PI and the sample according to GB / T17671, and the activity index of red mud powder R was calculated to be 62.9%.

[0052] Comparative Example 2 Bayer process red mud was dried in a drying oven at 200℃ until the moisture content was less than 1.0%, and carbide slag was dried in a drying oven at 105℃ until the moisture content was less than 1.0%. Then, they were ground to a fineness of 2.5% (80μm) to obtain red mud powder R and carbide slag powder C. The red mud powder and carbide slag powder were mixed at a mass ratio of 90:10 and calcined at 950℃ for 4 hours to obtain active mixture R90 / C10.

[0053] According to the GB / T21372 test method for physical properties of silicate cement clinker, 3.2% natural gypsum was added to the clinker during production, utilizing a φ500mm... A 500mm standard test mill was used to grind silicate cement PI. 30wt% of active admixture R90 / C10 was added to the silicate cement PI to prepare a sample. Then, the mortar strength test was carried out on the silicate cement PI and the sample according to GB / T17671. The activity index of active admixture R90 / C10 was calculated to be 65.2%.

[0054] Comparative Example 3 Bayer process red mud was dried in a drying oven at 200℃ until the moisture content was less than 1.0%, and carbide slag was dried in a drying oven at 105℃ until the moisture content was less than 1.0%. Then, they were ground to a fineness of 2.5% of 80μm to obtain red mud powder R and carbide slag powder C. The red mud powder and carbide slag powder were mixed at a mass ratio of 85:15 and calcined at 950℃ for 4 hours to obtain active mixture R85 / C15.

[0055] According to the GB / T21372 test method for physical properties of silicate cement clinker, 3.2% natural gypsum was added to the clinker during production, utilizing a φ500mm... A 500mm standard test mill was used to grind silicate cement PI. 30wt% of active admixture R85 / C15 was added to the silicate cement PI to prepare a sample. Then, the mortar strength test was carried out on the silicate cement PI and the sample according to GB / T17671. The activity index of active admixture R85 / C15 was calculated to be 68.5%.

[0056] Comparative Example 4 Bayer process red mud was dried in a drying oven at 200℃ until the moisture content was less than 1.0%, and carbide slag was dried in a drying oven at 105℃ until the moisture content was less than 1.0%. Then, they were ground to a fineness of 2.5% (80μm) to obtain red mud powder R and carbide slag powder C. The red mud powder and carbide slag powder were mixed at a mass ratio of 60:40 and calcined at 950℃ for 4 hours to obtain active mixture R60 / C40.

[0057] According to the GB / T21372 test method for physical properties of silicate cement clinker, 3.2% natural gypsum was added to the clinker during production, utilizing a φ500mm... A 500mm standard test mill was used to grind silicate cement PI. 30wt% of active admixture R60 / C40 was added to the silicate cement PI to prepare a sample. Then, the mortar strength test was carried out on the silicate cement PI and the sample according to GB / T17671. The activity index of active admixture R60 / C40 was calculated to be 72.1%.

[0058] Effect Example The mortar strength test was conducted on the samples prepared in Examples 1-4 and Comparative Examples 1-4. The test results are shown in Table 3 below: Table 3. Compressive strength and activity index of samples obtained in Examples 1-4 and Comparative Examples 1-4

[0059] As shown in Table 3, the activity index of the red mud powder R in Comparative Example 1 was only 62.9%, while the activity index of the active mixtures prepared in Examples 1-4 was ≥74.0%, meeting the requirements of GB / T2842-2011 "Pozzolanic Admixtures for Cement" (≥60%) and GB / T1596 "Fly Ash for Cement and Concrete" (≥70%). A further active mixture was prepared by mixing 70% by weight of red mud (dried at 200℃ and ground to 80μm fineness, 2.5%) and 30% by weight of carbide slag (dried at 105℃ and ground to 80μm fineness, 2.5%), and then calcining at 950℃ for 4 hours. The resulting active mixture had an activity index of 81.8%, which was 18.9% higher than that of the red mud powder R without carbide slag.

[0060] The phase structure of the active mixture was characterized by XRD, and mineral composition analysis was performed. The results are shown in [Figure number missing]. Figure 1 .

[0061] Figure 1 The images show the XRD patterns of the active mixtures prepared in Examples 1-4 and Comparative Examples 1-4. Figure 1 It can be seen that the phase composition of red mud powder R (without carbide slag) and active mixture R70 / C30 (red mud with carbide slag at a mass fraction of 30%) is different after calcination at 950℃ for 4 hours. The XRD pattern of red mud powder R shows the presence of Fe2O3 (peak marked 1), and the characteristic peak of Fe2O3 is relatively obvious, indicating that Fe2O3 is one of the main phases in red mud powder after grinding and high-temperature calcination without carbide slag powder. In addition to the characteristic peak of Fe2O3, R70 / C30 also contains characteristic peaks of CaO (peak marker 2), Ca2Fe2O5 (peak marker 3), C2S (peak marker 4), and C3A (peak marker 5). This indicates that when 70% by mass of red mud powder and 30% by mass of carbide slag powder are mixed, the components in the carbide slag participate in the reaction during high-temperature calcination, resulting in the formation of new phases such as CaO, Ca2Fe2O5, C2S, and C3A in the material. Compared with red mud powder R, R70 / C30 has more types of phases, indicating that the incorporation of carbide slag alters the phase composition of the red mud after high-temperature calcination.

[0062] This invention features a simple, economical, and environmentally friendly process that requires no chemical additives or pre-treatment of the red mud for dealkalization. By mixing carbide slag and red mud in a specific ratio and then calcining them at high temperatures, a new phase is generated through the reaction between the chemical components of the two materials, thereby improving the activity of the Bayer process red mud and converting the two types of waste slag into a cementitious composite material that can be used directly.

[0063] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for improving the activity of Bayer process red mud, characterized in that, Includes the following steps: S1. Dry the Bayer process red mud and carbide slag separately until the moisture content is less than 1.0%, then grind them to obtain red mud powder and carbide slag powder; S2. Mix the red mud powder with the carbide slag powder and calcine to obtain an active mixture; The mass ratio of the red mud powder to the calcium carbide slag powder is 65-80:20-35; The chemical composition of the active mixture includes CaO, Ca2Fe2O5, C2S, C3A, and Fe2O3.

2. The method for improving the activity of Bayer process red mud according to claim 1, characterized in that, The Bayer process red mud contains 5.0% water of crystallization.

3. The method for improving the activity of Bayer process red mud according to claim 1, characterized in that, In step S1, the drying process includes drying Bayer red mud at 200°C in a drying oven and drying calcium carbide slag at 105°C in a drying oven.

4. The method for improving the activity of Bayer process red mud according to claim 1, characterized in that, In step S1, the grinding involves grinding Bayer red mud and carbide slag to a fineness of 2.5% (80 μm).

5. The method for improving the activity of Bayer process red mud according to claim 1, characterized in that, In step S2, the specific steps for obtaining the active mixture include: The red mud powder and the calcium carbide slag powder are mixed at a mass ratio of 80:20, 75:25, 70:30 or 65:35 and calcined at 950°C for 4 hours to obtain the active mixture.

6. A method for evaluating the activity of an active mixture as described in any one of claims 1-5, characterized in that, Includes the following steps: S1. Mix clinker with natural gypsum, grind, and obtain silicate cement; S2. A sample was prepared by adding 30 wt% of the active admixture to silicate cement; S3. Conduct mortar strength tests on silicate cement and samples; S4. Calculate the activity index of the reactive mixture using the following formula: A= In the formula: A represents the activity index of the active mixture, %; The compressive strength of the sample after 28 days, in MPa; The value represents the 28-day compressive strength of silicate cement, in MPa.

7. The method for evaluating the activity of active mixtures according to claim 6, characterized in that, The silicate cement is composed of 96.8 wt% clinker and 3.2 wt% natural gypsum.

8. The method for evaluating the activity of active mixtures according to claim 6, characterized in that, The cooked food was prepared in-house.

9. The method for evaluating the activity of active mixtures according to claim 6, characterized in that, The mortar strength test shall be conducted in accordance with GB / T17671.

10. The method for evaluating the activity of active mixtures according to claim 6, characterized in that, The activity index of the active mixture is ≥74.0%.

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