An acidification-heat activation based red mud-based salt-activated cementitious material, a preparation method and application thereof

Abstract

The application discloses a kind of based on acidification-thermal activation's red mud base salt excitation cementitious material and its preparation method and application, belong to solid waste base cementitious material technical field.The red mud base salt excitation cementitious material provided by the application includes 98~99% red mud-solid waste gypsum complex, 0.2~0.5% water reducing agent and 0.5~1.8% early strength agent by mass fraction;Red mud-solid waste gypsum complex is prepared by thermal activation of acidified red mud and solid waste gypsum with mass ratio of (8~10):1, and the acidified red mud is obtained by neutralizing composite dealkalizer and Bayer red mud;Composite dealkalizer includes 60~70% carboxylic acid component and 30~40% sulfonic acid component.The utilization rate of Bayer red mud is as high as 85% or more, solving the problem of low utilization rate of Bayer red mud in the prior art;At the same time, the obtained cementitious material has good early strength and late strength, and the performance is equivalent to or even better than the existing cement mortar.

Description

A red mud-based salt-activated cementitious material based on acidification-thermal activation, its preparation method and application Technical Field

[0001] This invention relates to the field of solid waste-based cementitious materials technology, and in particular to a red mud-based salt-activated cementitious material based on acidification-thermal activation, its preparation method, and its application. Background Technology

[0002] The information disclosed in the background section of this invention is intended only to enhance the understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Red mud is a high-moisture, alkaline solid waste discharged during the extraction of alumina in the aluminum industry. Its large stockpiles and comprehensive utilization rate of less than 10% result in significant open-air dumping of red mud, occupying substantial land resources, generating large amounts of dust, severely polluting groundwater, causing soil alkalization, and impacting agricultural and forestry irrigation and drinking water for humans and livestock, posing a threat to food safety and public health. Therefore, the resource utilization of red mud is urgently needed. Based on different alumina production processes, red mud is classified into three categories: Bayer process red mud, sintering process red mud, and combined process red mud. Bayer process red mud is typically obtained from processing low-silica bauxite and mainly consists of iron oxide, alumina, and alkali. It has a high pH value and poor activity, thus posing a greater challenge to its resource utilization.

[0004] Currently, existing technologies report technical solutions for preparing alkali-activated / geopolymer-based cementitious materials using Bayer red mud waste. However, due to the high alkali content in Bayer red mud, the end product suffers from severe efflorescence, leading to performance degradation and potential environmental pollution risks. Furthermore, the utilization rate of red mud is low, making it difficult to achieve large-scale, high-value-added utilization of Bayer process red mud. Therefore, it is urgent to provide a new method for red mud dealkali removal and realize the high-value, green, large-scale utilization of red mud. Summary of the Invention

[0005] In view of this, the present invention provides a red mud-based salt-activated cementitious material based on acidification-thermal activation, its preparation method and application, which solves the problems of efflorescence and alkaline pollution of red mud-based alkali-activated / geopolymer cementitious materials. Furthermore, the Bayer red mud has a high utilization rate, and the prepared red mud-based salt-activated cementitious material has the advantages of low cost, high mechanical strength and green environmental protection.

[0006] In a first aspect, the present invention provides a red mud-based salt-activated cementitious material based on acidification-thermal activation, comprising, by mass fraction, 98-99% red mud-solid waste gypsum composite, 0.2-0.5% water-reducing agent and 0.5-1.8% early-strength agent;

[0007] The red mud-solid waste gypsum composite is prepared by thermal activation of acidified red mud and solid waste gypsum in a mass ratio of (8-10):1. The acidified red mud is obtained by neutralizing Bayer red mud with a composite dealkalizing agent. The composite dealkalizing agent, by mass fraction, includes 60-70% carboxylic acid components and 30-40% sulfonic acid components.

[0008] Preferably, the early strength agent is selected from silicate cement or sulfoaluminate cement.

[0009] Preferably, the water-reducing agent is selected from polycarboxylate water-reducing agents or naphthalene-based water-reducing agents.

[0010] Preferably, the solid waste gypsum is selected from one or more of phosphogypsum, desulfurization gypsum, titanium gypsum, fluorogypsum, citric acid gypsum, mirabilite gypsum, or salt gypsum.

[0011] Preferably, the molar ratio of the composite dealkali agent to the alkali component in Bayer red mud is (1-1.1):1.

[0012] Preferably, the carboxylic acid component is selected from one or more of acetic acid, citric acid, oxalic acid, propionic acid, or tartaric acid; the sulfonic acid component is selected from one or more of aminoethanesulfonic acid, aromatic sulfonic acid, naphthalenesulfonic acid, or methanesulfonic acid.

[0013] Secondly, the present invention provides a method for preparing the above-mentioned red mud-based salt-activated cementitious material based on acidification-thermal activation, comprising the following steps:

[0014] Bayer red mud was mixed with water to prepare red mud slurry. A composite dealkalizing agent was added to the red mud slurry and stirred to obtain acidified red mud slurry.

[0015] Solid waste gypsum was added to acidified red mud slurry and mixed evenly. After drying, it was thermally activated to obtain red mud-solid waste gypsum composite.

[0016] The red mud-solid waste gypsum composite, water-reducing agent, and early strength agent are mixed evenly to obtain the final product.

[0017] Preferably, the water-cement ratio of the red mud slurry is 0.4 to 0.6.

[0018] Preferably, in the steps of sequentially performing filtration and washing after stirring, the stirring time is 20 to 50 minutes.

[0019] Preferably, the thermal activation step specifically involves heating to 200-300°C at a heating rate of 5-15°C / min, holding the temperature for activation for 2-4 hours, and then cooling to obtain the product.

[0020] Thirdly, the present invention provides the application of the above-mentioned acid-thermal activated red mud-based salt-activated cementitious materials or the acid-thermal activated red mud-based salt-activated cementitious materials prepared by the above preparation method in the field of construction engineering.

[0021] Compared with the prior art, the present invention has achieved the following beneficial effects:

[0022] (1) This invention uses a composite dealkali agent composed of carboxylic acid (R-COOH) and sulfonic acid (R-SO3H) to neutralize red mud. The neutralization process generates organic sodium salt, which can efficiently solidify sodium ions and has a high activation effect on the red mud co-solid waste system. This avoids the problem of efflorescence of the red mud-based salt-activated cementitious material, thus avoiding adverse environmental impacts and ensuring the performance stability of the cementitious material.

[0023] (2) The red mud-based salt-activated cementitious material of the present invention has a utilization rate of Bayer red mud of up to 85% or more, which solves the problem of low utilization rate of Bayer red mud in the prior art, and the total solid waste utilization rate is up to 95% or more. At the same time, the red mud-based salt-activated cementitious material obtained has good early strength and late strength, and its performance is comparable to or even better than that of existing cement mortar. It has good application prospects in the field of construction engineering (such as road engineering, bridge engineering, tunnel engineering, mining engineering, etc.) and realizes the high-value utilization of solid waste. Attached Figure Description

[0024] The accompanying drawings, which form part of this specification, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention and do not constitute an undue limitation thereof. Obviously, those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0025] Figure 1 shows the mineral phase composition analysis of the acidified red mud and the original Bayer red mud in Example 1 of this invention. Detailed Implementation

[0026] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0027] This invention provides a red mud-based salt-activated cementitious material based on acidification-thermal activation, comprising, by mass fraction, 98-99% red mud-solid waste gypsum composite, 0.2-0.5% water-reducing agent, and 0.5-1.8% early-strength agent;

[0028] The red mud-solid waste gypsum composite is prepared by thermal activation of acidified red mud and solid waste gypsum in a mass ratio of (8-10):1. The acidified red mud is obtained by neutralizing Bayer red mud with a composite dealkalizing agent. The composite dealkalizing agent, by mass fraction, includes 60-70% carboxylic acid components and 30-40% sulfonic acid components.

[0029] This invention is based on the activation mechanism of salt components on silica-alumina-calcium components, and rationally utilizes the alkaline components in red mud. Under the action of an acidic composite dealkalizing agent composed of carboxylic acid and sulfonic acid components, the alkaline components in red mud undergo an acid-base neutralization reaction to generate organic sodium salts, thereby avoiding the adverse effects of the alkaline components in red mud. The organic sodium salts generated by the neutralization reaction achieve efficient solidification of sodium ions and have a high activation effect on the red mud-co-solid waste system, thus significantly reducing the amount of alkaline activating components added to red mud-based salt-activated cementitious materials. On the one hand, this improves the utilization rate of red mud, and on the other hand, it avoids the occurrence of efflorescence.

[0030] The solid waste gypsum added in this invention contains CaSO4. Under thermal activation, the calcium components in the solid waste gypsum can undergo a synergistic activation reaction with the silica-alumina components in the red mud, thereby improving the physical and mechanical properties of the end product. At the same time, the thermal activation method can fully mix the silica-alumina-calcium components in the red mud-solid waste gypsum with the salt components generated by acidification, thereby generating red mud-based salt-activated cementitious materials in one step, avoiding the need for secondary addition of salt activators. In addition, the sulfate ions in the solid waste gypsum also have a salt activation effect, which can further enhance the activation effect of the salt activator on the silica-alumina-calcium components in the red mud-solid waste gypsum system.

[0031] The water-reducing agent and early-strength agent added in this invention can further improve the slurry properties and mechanical strength of red mud-based cementitious materials. The early-strength agent is selected from silicate cement or sulfoaluminate cement, which can improve the early strength of red mud-based cementitious materials; the water-reducing agent is selected from any one of polycarboxylate water-reducing agents or naphthalene-based water-reducing agents.

[0032] In this invention, the solid waste gypsum is selected from one or more of phosphogypsum, desulfurization gypsum, titanium gypsum, fluorogypsum, citric acid gypsum, mirabilite gypsum, or salt gypsum. All of the above solid waste gypsums use CaSO4 as their main component.

[0033] In this invention, the molar ratio of the composite dealkali agent to the alkaline components in Bayer red mud is (1-1.1):1, more preferably (1.02-1.08):1. A slight excess of the composite dealkali agent ensures complete neutralization of the alkaline components in the Bayer red mud. The alkaline components in the Bayer red mud mentioned in this invention refer to sodium carbonate, sodium bicarbonate, nepheline, etc. This invention does not impose any special limitations on the method for determining the content of alkaline components in Bayer red mud. Preferably, this invention uses X-ray fluorescence spectrometry to test the chemical composition of the red mud, and calculates the alkali content based on the Na₂O content.

[0034] In this invention, the carboxylic acid component is selected from one or more of acetic acid, citric acid, oxalic acid, propionic acid, or tartaric acid; the sulfonic acid component is selected from one or more of aminoethanesulfonic acid, aromatic sulfonic acid, naphthalenesulfonic acid, or methanesulfonic acid. This invention has found that the composite dealkali removal agent composed of the carboxylic acid component and the sulfonic acid component has a superior dealkali removal effect, and the subsequently generated organic salt has a high solidification effect on sodium ions. Furthermore, the generated organic salt has a strong enhancing effect on the gelling activity of the red mud synergistic multi-source solid waste system.

[0035] This invention also provides a method for preparing the above-mentioned red mud-based salt-activated cementitious material based on acidification-thermal activation, comprising the following steps:

[0036] Bayer red mud was mixed with water to prepare red mud slurry. A composite dealkalizing agent was added to the red mud slurry and stirred to obtain acidified red mud slurry.

[0037] Solid waste gypsum was added to acidified red mud slurry and mixed evenly. After drying, it was thermally activated to obtain red mud-solid waste gypsum composite.

[0038] The red mud-solid waste gypsum composite, water-reducing agent, and early strength agent are mixed evenly to obtain the final product.

[0039] In this invention, the water-cement ratio of the red mud slurry is 0.4–0.6. Adding too much water will lead to waste, while adding too little water will result in poor fluidity of the red mud slurry, which is not conducive to the neutralization reaction.

[0040] In the steps of stirring followed by filtration and washing as described in this invention, the stirring time is 20–50 minutes. Stirring can be carried out at room temperature. During the stirring process, the alkaline components in the red mud undergo a neutralization reaction with the composite dealkalizing agent.

[0041] The present invention does not impose any special restrictions on the steps of stirring, mixing, drying, and uniform mixing; the operation methods commonly used by those skilled in the art can be adopted.

[0042] In this invention, the thermal activation step specifically involves heating to 200-300°C at a heating rate of 5-15°C / min, holding the temperature for activation for 2-4 hours, and then cooling to obtain the final product. This invention does not impose any special limitations on the cooling method, such as natural cooling or air cooling. The activation temperature of this invention is below 300°C to avoid the decomposition of the generated organic salts. Furthermore, to improve the activation effect, the holding activation temperature of this invention is further preferably 280-300°C.

[0043] The present invention also provides the application of the above-mentioned acid-thermal activated red mud-based salt-activated cementitious materials or the acid-thermal activated red mud-based salt-activated cementitious materials prepared by the above preparation method in the field of construction engineering.

[0044] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0045] In the following examples, the early-strength agent is silicate cement, and the water-reducing agent is polycarboxylate superplasticizer. The chemical composition of the red mud was tested using X-ray fluorescence spectrometry, and the alkali content was calculated based on the Na₂O content.

[0046] Example 1

[0047] This embodiment provides a method for preparing red mud-based salt-activated cementitious materials based on acidification-thermal activation, including the following steps:

[0048] (1) Calculate the total amount of alkali components in Bayer red mud and prepare the red mud into Bayer red mud slurry with a water-cement ratio of 0.5;

[0049] (2) Mix 60 parts of acetic acid and 40 parts of aminoethanesulfonic acid thoroughly to prepare a composite dealkalizing agent for later use;

[0050] (3) The composite dealkali agent is added to the Bayer red mud slurry at a molar ratio of 1.05:1 to the total amount of the composite dealkali agent and the Bayer red mud alkali component. The mixture is stirred for 30 minutes at room temperature (25±3℃) to obtain the acidified red mud.

[0051] (4) Add desulfurized gypsum powder to the acidified red mud slurry at a mass ratio of 8:1 (acidified red mud to desulfurized gypsum), stir thoroughly and set aside.

[0052] (5) The red mud-desulfurized gypsum composite slurry is heat-treated in a drying equipment, wherein the heating rate is 10℃ / min, the activation temperature is 300℃, the activation time is 3h, and then it is air-cooled to room temperature to obtain the heat-activated red mud-desulfurized gypsum composite.

[0053] (6) Mix 98 parts of red mud-desulfurized gypsum composite, 0.2 parts of water-reducing agent, and 1.8 parts of early strength agent thoroughly to obtain red mud-based salt-activated cementitious material.

[0054] X-ray diffraction (XRD) tests were performed on the acidified red mud obtained in step (3) and the original Bayer red mud. As shown in Figure 1, it can be seen that after the red mud was acidified, the diffraction peaks of mineral phases such as nepheline, gibbsite, and hematite in the system disappeared, indicating that the alkaline minerals in the red mud participated in the neutralization reaction and generated salt components with the acidic composite dealkalizing agent. The salt components can participate in the hydration reaction of the red mud-based salt-induced cementitious materials in the later stage, thereby preventing the occurrence of problems such as efflorescence and alkali pollution of traditional red mud-based cementitious materials.

[0055] Example 2

[0056] The difference between this embodiment and Example 1 is that the composite dealkalizing agent in this embodiment is 70 parts acetic acid and 30 parts aminoethanesulfonic acid.

[0057] Example 3

[0058] The difference between this embodiment and Embodiment 1 is that phosphogypsum is used instead of desulfurized gypsum in this embodiment.

[0059] Example 4

[0060] The difference between this embodiment and Embodiment 1 is that the mass ratio of red mud to desulfurized gypsum in this embodiment is 10:1.

[0061] Example 5

[0062] The difference between this embodiment and Embodiment 1 is that the thermal activation temperature of the red mud-desulfurized gypsum composite in this embodiment is 200℃.

[0063] Example 6

[0064] The difference between this embodiment and Embodiment 1 is that this embodiment contains 99 parts of red mud-desulfurized gypsum composite, 0.5 parts of water-reducing agent, and 0.5 parts of early strength agent.

[0065] Comparative Example 1

[0066] This comparative example is a standard mortar prepared with 42.5# ordinary Portland cement. The specific preparation method refers to GBT17671-2021 Cement Mortar Strength Test Method.

[0067] Comparative Example 2

[0068] The difference between this comparative example and Example 1 is that the dealkalizing agent in this comparative example is acetic acid, which does not contain aminoethanesulfonic acid.

[0069] Comparative Example 3

[0070] The difference between this comparative example and Example 1 is that the dealkalizing agent in this comparative example is aminoethanesulfonic acid, and it does not contain acetic acid.

[0071] Comparative Example 4

[0072] The difference between this comparative example and Example 1 is that the dealkalizing agent in this comparative example is hydrochloric acid.

[0073] Test case

[0074] The performance of the cementitious materials in Examples 1 to 6 and Comparative Examples 1 to 4 was tested in accordance with the "Test Methods for Basic Performance of Building Mortar" (JGJ / T 70-2009), and the results are shown in Table 1.

[0075] Table 1. Test results of cementitious material properties

[0076]

[0077] As can be seen from Table 1, the sodium acetate and sodium sulfonate generated after acid-base neutralization have a synergistic activating effect on the gelling activity of the red mud-desulfurized gypsum system. As can be seen from Comparative Example 4, after hydrochloric acid reacts with the alkaline components in red mud, sodium chloride is generated. The activating effect of chloride on the red mud-desulfurized gypsum system is weak, so the performance of the end product is poor.

[0078] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A red mud-based salt-activated cementitious material based on acidification-thermal activation, characterized in that, The composition comprises, by mass fraction, 98-99% red mud-solid waste gypsum composite, 0.2-0.5% water-reducing agent, and 0.5-1.8% early-strength agent; the red mud-solid waste gypsum composite is obtained by thermal activation of acidified red mud and solid waste gypsum in a mass ratio of (8-10):1, wherein the acidified red mud is obtained by neutralizing Bayer red mud with a composite dealkalizing agent; the composite dealkalizing agent comprises, by mass fraction, 60-70% carboxylic acid components and 30-40% sulfonic acid components.

2. The red mud-based salt-activated cementitious material based on acidification-thermal activation as described in claim 1, characterized in that, The early strength agent is selected from silicate cement or sulfoaluminate cement; the water-reducing agent is selected from polycarboxylate water-reducing agent or naphthalene-based water-reducing agent.

3. The red mud-based salt-activated cementitious material based on acidification-thermal activation as described in claim 1, characterized in that, The solid waste gypsum is selected from one or more of phosphogypsum, desulfurization gypsum, titanium gypsum, fluorogypsum, citric acid gypsum, mirabilite gypsum, or salt gypsum.

4. The red mud-based salt-activated cementitious material based on acidification-thermal activation as described in claim 1, characterized in that, The molar ratio of the composite dealkali agent to the alkali component in Bayer red mud is (1~1.1):

1.

5. The red mud-based salt-activated cementitious material based on acidification-thermal activation as described in claim 1, characterized in that, The carboxylic acid component is selected from one or more of acetic acid, citric acid, oxalic acid, propionic acid, or tartaric acid; the sulfonic acid component is selected from one or more of aminoethanesulfonic acid, aromatic sulfonic acid, naphthalenesulfonic acid, or methanesulfonic acid.

6. The preparation method of red mud-based salt-activated cementitious materials according to any one of claims 1 to 5, characterized in that, The process includes the following steps: preparing a red mud slurry by adding water to Bayer red mud; adding a composite dealkali agent to the red mud slurry and stirring to obtain an acidified red mud slurry; adding solid waste gypsum to the acidified red mud slurry and mixing well; drying and then thermally activating to obtain a red mud-solid waste gypsum composite; and mixing the red mud-solid waste gypsum composite, water-reducing agent, and early strength agent evenly to obtain the final product.

7. The preparation method according to claim 6, characterized in that, The water-cement ratio of the red mud slurry is 0.4~0.

6.

8. The preparation method according to claim 6, characterized in that, The stirring time is 20-50 minutes.

9. The preparation method according to claim 6, characterized in that, The thermal activation step specifically involves heating to 200-300°C at a heating rate of 5-15°C / min, holding the temperature for 2-4 hours, and then cooling to obtain the final product.

10. The application of the acidification-thermal activation-based red mud-based salt-activated cementitious material as described in any one of claims 1 to 5, or the acidification-thermal activation-based red mud-based salt-activated cementitious material prepared by the preparation method described in any one of claims 6 to 9, in the field of construction engineering.

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