A red mud-based low-carbon composite cement and a preparation method thereof

Abstract

This invention relates to the field of novel low-carbon composite cement and solid waste resource utilization technology, specifically to a red mud-based low-carbon composite cement and its preparation method. The raw materials for this red mud-based low-carbon composite cement include red mud, auxiliary cementitious materials, gypsum-based solid waste, alkali activator, retarder, and interface reinforcing agent. It possesses compressive strength comparable to or even higher than 425 or 525 cement, with a red mud content ≥30wt% and an alkali activator content as low as 3wt%–8wt%. This not only achieves large-scale resource utilization of red mud but also significantly reduces production costs. Simultaneously, the cement hydration products have a good shielding effect against radioactivity, ensuring that the radioactivity of the hardened cement still meets national standards even with the large-scale incorporation of red mud. Moreover, the preparation method of this cement is simple, requiring neither red mud dealkalization nor high-temperature calcination, truly achieving low-carbon, low-energy-consumption, and low-cost green and environmentally friendly cement production.

Description

Technical Field

[0001] This invention relates to the fields of novel low-carbon composite cement and solid waste resource utilization technology, specifically to a red mud-based low-carbon composite cement and its preparation method. Background Technology

[0002] Cement is an essential building material, and my country's socio-economic development relies heavily on its support. However, traditional cement production processes suffer from high emissions, high energy consumption, and resource dependence, which are inconsistent with the concept of low-carbon development. Therefore, the research and development of low-carbon cement has become particularly important.

[0003] Alkali-activated cement is a low-carbon, environmentally friendly cement prepared based on alkali activation technology. It includes alkali-activated slag cement and geopolymer cement, and is mostly composed of industrial waste such as fly ash and mineral powder, or natural minerals, mixed with a certain amount of activator. Compared with ordinary silicate cement, the CO2 emissions from the preparation of alkali-activated cement can be reduced by about 70%. However, in practical applications, compared with the traditional method of hardening silicate cement by mixing with water, alkali-activated cement requires the addition of a larger amount of alkali activator to set and solidify. Currently, the most commonly used alkali activator in the preparation of alkali-activated cement is an alkaline activator composed of solid alkali powder (sodium hydroxide or potassium hydroxide) and readily soluble sodium silicate. The use of this type of alkali activator significantly increases the manufacturing cost of alkali-activated cement, limiting its promotion and use.

[0004] Red mud is a highly alkaline solid waste generated during alumina production. For every ton of alumina produced, 1 to 1.5 tons of red mud are generated. The dumping of red mud not only wastes land resources, but also, due to its highly alkaline nature, its chemical components seep into the soil and groundwater, severely polluting the ecological environment surrounding the dumping sites. Therefore, there is an urgent need to develop a low-cost, harmless method for the large-scale disposal and utilization of red mud.

[0005] Although existing technologies exist for using red mud in the preparation of roadbed water-stabilized layers or concrete and other building materials, its strong alkalinity makes it prone to blooming when used as a structural material in the building materials field. Therefore, de-alkalization pretreatment is required during the preparation of structural materials, which complicates the process. Furthermore, some trace elements in red mud, such as radium, thorium, and potassium, are radioactive. Direct use in roadbeds and other building materials could lead to excessive radiation levels. However, reducing the radiation of red mud is too costly. This limits the amount of red mud incorporated into building materials, generally to less than 20% of the total mass of the prepared material. In summary, the strong alkalinity and radioactivity of red mud restrict its reuse, leading to increasing accumulation of red mud from aluminum production, posing a serious threat to the ecological environment and public health. Summary of the Invention

[0006] In view of this, the present invention provides a red mud-based low-carbon composite cement and its preparation method. The red mud content in the red mud-based low-carbon composite cement is greater than 30 wt%, the amount of alkali activator is only 3 wt% to 8 wt%, and the compressive strength is greater than or equal to that of silicate 425 cement or silicate 525 cement. The preparation method of the red mud-based low-carbon composite cement is simple and does not require high-temperature calcination, thus truly realizing the green and environmentally friendly preparation of cement with low carbon, low energy consumption, and low cost.

[0007] To solve the above technical problems, this invention provides a red mud-based low-carbon composite cement, the raw materials of which include:

[0008] Cementitious components: including 30wt% to 65wt% red mud, 10wt% to 50wt% auxiliary cementitious materials, and 5wt% to 20wt% gypsum-based solid waste;

[0009] Activator component: includes an alkali activator, wherein the mass of the activator component is 3% to 8% of the mass of the gelling component;

[0010] Admixture components: including retarders and interface enhancers;

[0011] The auxiliary cementing material includes at least one of active silicate and active aluminosilicate; the red mud has a particle size of 48–74 μm.

[0012] The red mud-based low-carbon composite cement provided by this invention uses red mud, auxiliary cementitious materials, and gypsum-based solid waste as cementing components. The red mud has a particle size of 48–74 μm. If the particle size is too large, the alkalinity and activity of the red mud cannot be released; if the particle size is too small, the water demand will increase during subsequent use, thus affecting the mechanical properties of the cement. In this red mud-based low-carbon composite cement, red mud and an alkali activator are released together to form an alkaline environment. The auxiliary cementitious materials and gypsum-based solid waste raw materials depolymerize and dissolve in this alkaline environment. The ionic substances formed by dissolution further recombine to form two-dimensional and three-dimensional polymeric aluminosilicate materials. This material has cementing properties, which can cement and encapsulate the micro-reacting red mud, gypsum-based solid waste, and other raw materials together, thereby inhibiting the release of harmful substances and radioactivity. This invention utilizes highly alkaline... Red mud is used as a basic activator, thereby reducing the amount of the more expensive alkali activator to 3wt%–8wt%, saving production costs. In addition, this invention uses retarders and interface reinforcing agents as admixtures. The addition of retarders can delay the hydration and setting of cement, thus avoiding cracking caused by excessively rapid setting of the cement surface. As for interface reinforcing agents, since not all raw materials can completely react during the actual hydration reaction of red mud-based low-carbon composite cement, an interfacial transition region will be generated between the reacted and unreacted raw materials, affecting the final mechanical properties of the cement. The addition of interface reinforcing agents can increase the strength of the interfacial transition region, thereby reducing the impact of the interfacial transition region on the mechanical properties of red mud-based low-carbon composite cement.

[0013] In conjunction with the first aspect, the mass of the retarder is 0.1% to 1% of the mass of the gelling component, preferably 0.5%.

[0014] In conjunction with the first aspect, the mass of the interface reinforcing agent is 0.2% to 0.5% of the mass of the gelling component.

[0015] The above-mentioned dosage range of retarders and interface enhancers can improve the overall mechanical properties of the resulting red mud-based low-carbon composite cement.

[0016] In conjunction with the first aspect, the retarder is at least one selected from sodium carboxymethyl cellulose, tartaric acid, and sodium hexametaphosphate. The aforementioned retarder exhibits excellent retarding properties while having virtually no impact on the strength of the cement product.

[0017] In conjunction with the first aspect, the interface reinforcing agent is at least one selected from xanthan gum, triethylamine, silane coupling agent, borax, and sodium aluminate. During their research, the inventors discovered that the aforementioned interface reinforcing agent can produce a strengthening effect even at low dosages, and can also inhibit cracking of cement test blocks without affecting the setting time of the cement product.

[0018] In conjunction with the first aspect, the red mud includes at least one of Bayer process red mud, sintering process red mud, and combined process red mud. Depending on the aluminum industry production process, different types of red mud can be obtained, such as Bayer process red mud, sintering process red mud, and combined process red mud. The red mud-based low-carbon composite cement provided by this invention can be used for any type of red mud.

[0019] In conjunction with the first aspect, the particle size of the auxiliary cementitious material is no greater than 48 μm. Auxiliary cementitious materials within this particle size range have higher activity and better dispersibility, which can make red mud-based low-carbon composite cement have higher reactivity.

[0020] In conjunction with the first aspect, the active silicate includes at least one of blast furnace slag, yellow phosphorus slag, and silicate cement. Blast furnace slag, yellow phosphorus slag, and silicate cement can react and dissolve ionic silicates in water or a weakly alkaline solution, which then recombine to form two-dimensional silicate gel molecular chains, producing gelling properties, binding the raw material particles, and hardening and shaping to generate strength.

[0021] In conjunction with the first aspect, the active aluminosilicate includes at least one of metakaolin, fly ash, and volcanic ash. These raw materials possess excellent volcanic ash properties, and in an alkaline environment, they can release ionic aluminosilicates, which then recombine to form three-dimensional aluminosilicate gel molecular chains, exhibiting gelling properties, hardening, and generating strength.

[0022] In conjunction with the first aspect, the particle size of the gypsum-based solid waste is no greater than 48 μm. Gypsum-based solid waste within this particle size range has a moderate water requirement and a controllable reaction rate, making it suitable for the workability control of cement products.

[0023] In conjunction with the first aspect, the gypsum-based solid waste includes at least one of desulfurized gypsum and phosphogypsum. Desulfurized gypsum and phosphogypsum mainly provide gypsum products for red mud-based low-carbon composite cement, which can reduce the hydration reaction rate on the one hand and promote early strength on the other.

[0024] In conjunction with the first aspect, the alkaline activator comprises 30% to 50% by mass of readily soluble sodium silicate, 10% to 20% by mass of sodium carbonate, and 30% to 50% by mass of hydroxide, wherein the hydroxide comprises at least one of sodium hydroxide and potassium hydroxide.

[0025] In conjunction with the first aspect, the cementitious component also includes 5 wt% to 30 wt% silicate cement. The silicate cement has the same function as the active silicate component, and its appropriate addition can improve the hydration reaction activity of red mud-based low-carbon composite cement.

[0026] The second aspect of the present invention provides a method for preparing the above-mentioned red mud-based low-carbon composite cement, specifically: mixing and grinding the raw materials evenly, and passing them through a sieve with a pore size of 74 μm to obtain red mud-based low-carbon composite cement.

[0027] The preparation method provided by this invention is simple and does not require high-temperature calcination. It only requires mixing and grinding the raw materials to a certain fineness range to obtain red mud-based low-carbon composite cement, realizing the green and environmentally friendly preparation of cement that is truly low-carbon, low-energy-consumption, and low-cost, and is easy to scale up.

[0028] A third aspect of this invention provides the application of the above-described red mud-based low-carbon composite cement, or the red mud-based low-carbon composite cement prepared by the above method, in concrete, dry-mixed mortar, blocks, and / or road and bridge construction. In practical applications, the red mud-based low-carbon composite cement only needs to be mixed with water and stirred until homogeneous, similar to the method of using existing cement. The compressive strength of this red mud-based low-carbon composite cement after setting can be equal to or even higher than that of silicate 425 cement or silicate 525 cement, and it can replace cement in existing building materials.

[0029] The beneficial effects of this invention are as follows: The compressive strength of the red mud-based low-carbon composite cement provided by this invention is greater than or equal to that of silicate 425 cement or silicate 525 cement, and it can be used as a substitute for existing cement. The red mud content in the obtained cement is greater than 30 wt%, but the radioactivity of the cement still meets the national standard requirements. Moreover, the solid waste content in the obtained cement can reach up to 90 wt%, while the alkali activator dosage is only 3 wt% to 8 wt%, which achieves efficient utilization of solid waste while reducing production costs. In addition, the preparation method of the red mud-based low-carbon composite cement provided by this invention is simple. The red mud does not need to undergo de-alkalization pretreatment before use, and the obtained cement does not need to undergo a high-temperature calcination step, truly realizing the green and environmentally friendly preparation of cement with low carbon, low energy consumption, and low cost. The red mud-based low-carbon composite cement prepared according to this method is used in the same way as existing cement. After hydration and setting, no heat preservation is required, making it easy to achieve commercial and large-scale production and application. Attached Figure Description

[0030] Figure 1 This is a picture of a red mud-based low-carbon composite cement. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0032] In the following examples, the red mud used is Bayer process red mud, wherein the mass percentage of calcium oxide is 21.7%, the mass percentage of aluminum oxide is 31%, the mass percentage of silicon dioxide is 20.9%, and the particle size is 48-74 μm. Red mud in this particle size range can be obtained by drying at 110°C and then grinding.

[0033] Example 1

[0034] This embodiment provides a red mud-based low-carbon composite cement, the raw materials of which are shown in the table below:

[0035]

[0036] The preparation method is as follows:

[0037] After mixing the above raw materials in proportion, grind them in a ball mill for 0.5 hours and pass them through a 74μm sieve to obtain the red mud-based low-carbon composite cement product.

[0038] Example 2

[0039] This embodiment provides a red mud-based low-carbon composite cement, the raw materials of which are shown in the table below:

[0040]

[0041] The preparation method is the same as that in Example 1.

[0042] Example 3

[0043] This embodiment provides a red mud-based low-carbon composite cement, the raw materials of which are shown in the table below:

[0044]

[0045] The preparation method is the same as that in Example 1.

[0046] Example 4

[0047] This embodiment provides a red mud-based low-carbon composite cement, the raw materials of which are shown in the table below:

[0048]

[0049] The preparation method is the same as that in Example 1.

[0050] Comparative Example 1

[0051] This comparative example provides a red mud-based low-carbon composite cement, whose raw material formula is similar to that of Example 2, except that the particle size of the red mud used is greater than 74 μm, and the preparation method is the same as that in Example 1.

[0052] Comparative Example 2

[0053] This comparative example provides a red mud-based low-carbon composite cement, whose raw material formula is similar to that of Example 2, except that the particle size of the red mud used is less than 48 μm, and the preparation method is the same as that in Example 1.

[0054] Comparative Example 3

[0055] This comparative example provides a red mud-based low-carbon composite cement, the raw materials of which are shown in the table below:

[0056]

[0057] The preparation method is the same as that in Example 1.

[0058] Comparative Example 4

[0059] This comparative example provides a red mud-based low-carbon composite cement, the raw materials of which are shown in the table below:

[0060]

[0061] The preparation method is the same as that in Example 1.

[0062] Comparative Example 5

[0063] This comparative example provides a red mud-based low-carbon composite cement, the raw materials of which are shown in the table below:

[0064]

[0065]

[0066] The preparation method is the same as that in Example 1.

[0067] Comparative Example 6

[0068] This comparative example provides a red mud-based low-carbon composite cement, the raw materials of which are shown in the table below:

[0069]

[0070] The preparation method is the same as that in Example 1.

[0071] Test Example 1

[0072] The red mud-based low-carbon composite cements obtained in Examples 1-4 and Comparative Examples 1-6 were mixed with water at a mass ratio of 1:0.45 to obtain cementitious materials. The compressive strength of the obtained cementitious materials at different time points was measured and compared with the compressive strength of silicate cement 425 and silicate cement 525 at the corresponding time points. The results are shown in Table 1.

[0073] Table 1. Compressive strength of cementitious materials obtained from each embodiment and comparative example at different time points.

[0074]

[0075] As shown in Table 1, the compressive strength of the red mud-based low-carbon composite cement provided in Examples 1-3 of the present invention at 7 days and 28 days is comparable to or even higher than that of 425 cement at the same time. The compressive strength of the red mud-based low-carbon composite cement provided in Example 4 is comparable to that of 525 cement at 28 days. This indicates that the red mud-based low-carbon composite cement provided by the present invention can be used as a complete substitute for 425 cement or 525 cement.

[0076] Test Example 2

[0077] The red mud-based low-carbon composite cements obtained in Examples 1-4 and Comparative Examples 1-6 were mixed with water at a mass ratio of 1:0.45 to obtain cementitious materials, and their radioactivity was measured. The results are shown in Table 2.

[0078] Table 2. Radioactivity results of the cementitious materials obtained in each embodiment and comparative example.

[0079]

[0080] As can be seen from the data in Table 2, only when the types of raw materials and the corresponding component ratios are within the range provided by this invention can the red mud-based low-carbon composite cement after hydration reaction have a shielding effect on the radioactivity of the raw materials themselves. This indicates that the red mud-based low-carbon composite cement that can produce a three-dimensional gel structure was successfully prepared according to the raw material formula provided by this invention, thereby realizing the large-scale use of red mud.

[0081] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A red mud-based low-carbon composite cement, characterized in that, Raw materials include: Cementitious components: including 30wt%~65wt% red mud, 10wt%~50wt% auxiliary cementitious materials, and 5wt%~20wt% gypsum-based solid waste; Activator component: includes an alkali activator, wherein the mass of the activator component is 3% to 8% of the mass of the gelling component, and the alkali activator includes 30% to 50% by mass of fast-dissolving sodium silicate, 10% to 20% by mass of sodium carbonate and 30% to 50% by mass of hydroxide; Admixture components: including retarders and interface enhancers; The auxiliary cementitious material includes at least one of active silicate and active aluminosilicate; the active silicate includes at least one of blast furnace slag, yellow phosphorus slag and silicate cement; and the active aluminosilicate includes at least one of metakaolin, fly ash and pozzolanic. The red mud has a particle size of 48~74μm.

2. The red mud-based low-carbon composite cement as described in claim 1, characterized in that, The retarder is present in an amount of 0.1% to 1% of the mass of the gelling component; and / or The mass of the interface reinforcing agent is 0.2% to 0.5% of the mass of the gelling component.

3. The red mud-based low-carbon composite cement as described in claim 2, characterized in that, The retarder is at least one of sodium carboxymethyl cellulose, tartaric acid, and sodium hexametaphosphate; and / or The interface enhancer is at least one of xanthan gum, triethylamine, silane coupling agent, borax, and sodium aluminate.

4. The red mud-based low-carbon composite cement as described in claim 1, characterized in that, The red mud includes at least one of Bayer process red mud, sintering process red mud, and combined process red mud.

5. The red mud-based low-carbon composite cement as described in claim 1, characterized in that, The particle size of the auxiliary cementitious material is no greater than 48 μm.

6. The red mud-based low-carbon composite cement as described in claim 1, characterized in that, The particle size of the gypsum-based solid waste is no greater than 48 μm; and / or The gypsum-based solid waste includes at least one of desulfurized gypsum and phosphogypsum.

7. The red mud-based low-carbon composite cement as described in claim 1, characterized in that, The hydroxide includes at least one of sodium hydroxide and potassium hydroxide.

8. The red mud-based low-carbon composite cement according to any one of claims 1 to 7, characterized in that, The cementitious component also includes 5 wt% to 30 wt% silicate cement.

9. A method for preparing red mud-based low-carbon composite cement according to any one of claims 1 to 8, characterized in that, The raw materials are mixed and ground evenly, and then passed through a sieve with a pore size of 74μm to obtain red mud-based low-carbon composite cement.

10. The application of the red mud-based low-carbon composite cement according to any one of claims 1 to 8, or the red mud-based low-carbon composite cement prepared according to the preparation method of claim 9, in concrete, dry-mixed mortar, blocks, and / or roads and bridges, characterized in that, Simply mix the red mud-based low-carbon composite cement with water and stir until homogeneous before use.

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