A method of making a concrete admixture
By combining chemical and mechanical treatment with gas and ultrasonic technology, the activity of red mud is stimulated, and a highly active concrete admixture is prepared. This solves the problems of strength and durability of red mud when used in concrete, and realizes the resource utilization of red mud.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- SHANDONG SHITONG HIGHWAY CONSTR CO LTD
- Filing Date
- 2026-03-24
- Publication Date
- 2026-06-05
AI Technical Summary
Existing technologies are insufficient to effectively reduce the alkalinity of red mud and enhance its activity, leading to problems such as decreased strength, abnormal early setting, and reduced durability when it is used in concrete.
A highly active concrete admixture was prepared by employing a synergistic approach combining chemical, mechanical, gas, and ultrasonic methods. The surface of red mud was corroded by the synergistic acid etching effect of oxalic acid and phosphoric acid. The pH of the reaction system was controlled by carbon dioxide gas. The activity of the iron-aluminum phase was activated by hydrogen peroxide. Amorphous active products were formed by adding silica solution and calcined alum. The activity was maintained by freeze-drying.
This study achieved a reduction in the alkalinity and an increase in the activity of red mud, resulting in the preparation of a highly active admixture that can replace a portion of cement, improve concrete performance, and provide a new approach for the resource utilization of red mud.
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of industrial solid waste resource utilization and concrete admixture preparation, specifically relating to a method for preparing concrete admixtures. Background Technology
[0002] my country is a major industrial country with high solid waste production, large storage volume, and low utilization rate. This not only occupies vast amounts of land but also pollutes soil and groundwater, seriously impacting the ecological environment and human living safety. Red mud is the most significant solid waste generated during the alumina industry, primarily from the Bayer process. It is highly alkaline, hazardous, polluting, difficult to treat, and has a low utilization rate, making the harmless treatment and resource utilization of red mud an urgent priority. Building materials are the most abundant building materials, with extremely high annual production and consumption, making them a crucial pathway for the disposal and resource utilization of red mud. However, the low activity and high alkalinity of red mud severely limit its application in building materials. Direct application to concrete leads to problems such as decreased strength, abnormal early setting, and reduced durability. Currently, methods such as high-temperature calcination, mechanical grinding, and alkali activation are mainly used to improve the activity of red mud and reduce its adverse reactions. However, the activation effect is limited, making it difficult to prepare high-performance admixtures. Modified red mud volcanic ash has limited activity and is used in low quantities. Therefore, developing a red mud activation method that can reduce the alkalinity of red mud, enhance its pozzolanic activity, and maintain stable performance without adversely affecting concrete, and preparing high-performance admixtures, is of great significance for realizing its resource utilization. Summary of the Invention
[0003] To address the problems existing in the background technology, the present invention provides a method for preparing concrete admixtures based on the enhancement of red mud activity. This method achieves red mud activation through the synergistic effect of chemical, mechanical, gas, and ultrasonic measures, effectively reducing the alkalinity of red mud, stimulating its activity, and forming stable amorphous active products, ultimately preparing a highly active admixture suitable for concrete.
[0004] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing a concrete admixture includes the following steps: (1) Mix red mud, oxalic acid, phosphoric acid, dispersant and water to form a paste, and then place the paste in a grinding equipment for wet grinding until the specific surface area is 600~700 m² / kg to form slurry material A; The red mud is solid waste red mud produced by the Bayer process; The dispersant is a mixture of polycarboxylate superplasticizer and triethanolamine in a mass ratio of 2 to 4:1. When liquid polycarboxylate superplasticizer is used, its solid content is used for calculation. (2) Transfer the slurry material A obtained in step (1) from the grinding equipment to the stirring equipment, and introduce carbon dioxide gas to remove the air in the stirring equipment; after the carbon dioxide is filled, seal the equipment, and perform ultrasonic vibration and continuous slow stirring reaction under the condition of continuous carbon dioxide introduction. The ultrasonic frequency is 30~50kHz, the stirring speed is 30~120r / min, and the reaction time is 10~15min; (3) Add hydrogen peroxide to the reaction system of step (2), stir evenly, continue to pass carbon dioxide to fill the system, seal the equipment, and carry out ultrasonic vibration reaction. The ultrasonic frequency is 30~50kHz, and the reaction time is 1.2~1.5h; (4) Add silica solution to the reaction system of step (3), stir evenly, add calcined alum, stir evenly again, transfer to a freeze dryer for freeze drying, and then grind to a particle size of 700~800 μm. 2 / kg, to obtain the active concrete admixture of the present invention; The freeze-drying process consists of pre-freezing, sublimation drying, and desorption drying. The pre-freezing parameters are: -50~-60℃ temperature, rate of freezing 2~3℃ / min, and freezing time 8~12h. The sublimation drying parameters are: vacuum degree 10~30Pa, shelf temperature -20~-10℃, and time 24~48h. The desorption drying parameters are: vacuum degree 1~5Pa, shelf temperature 20~30℃, and time 8~12h.
[0005] Furthermore, the mass fractions of each raw material component in this invention are as follows: 100 portions of red mud, 3-5 parts oxalic acid 12-15 parts of phosphoric acid Dispersant 0.5~2 parts, 30-50 parts water 3-5 parts hydrogen peroxide 3-5 parts of silicic acid solution Add 5-8 parts of calcined alum; The hydrogen peroxide has a mass concentration of 25-30%; if the concentration is too high, it is unstable and easily decomposes. The concentration of the silicic acid solution is 1 mol to 2 mol / L.
[0006] In step (1) of this invention, the synergistic acid etching effect of oxalic acid and phosphoric acid is used to corrode the surface of red mud particles, promoting the dissolution of active substances such as iron, aluminum, and silicon in the iron-aluminum phase inside the red mud; among them, oxalic acid can effectively complex Ca in the red mud. 2+ Al 3+The presence of cations prevents the formation of precipitates and crystals; phosphoric acid reacts with the alkali dissolved in red mud to form phosphates, simultaneously acting as a alkali stabilizer, providing phosphate ions, and controlling pH; the dispersant improves grinding efficiency and prevents the crystal growth of the product, maintaining its micro-nano particle morphology and improving particle dispersion; wet ball milling enhances acid etching and facilitates temperature control of the material system during the reaction, making the reaction process controllable.
[0007] In step (2) of this invention, CO2 is introduced to control the pH of the entire reaction system, ensuring the reaction proceeds under weakly acidic conditions and avoiding drastic pH changes. In step (3), CO2 is continuously introduced in the presence of hydrogen peroxide, utilizing the carbonic acid formed by its dissolution and the dissolved Fe³⁺. + Al³ + The ionic reaction produces ferric carbonate and aluminum carbonate intermediates, the latter of which rapidly hydrolyzes to form highly reactive ferric hydroxide and aluminum hydroxide precipitates; the purpose of adding hydrogen peroxide is to activate the Fe²⁺ ions within the red mud. + Dissolved and oxidized to Fe3 + This not only changes the form of iron, which helps to generate highly active water-iron mineral phases, but more importantly, it destroys the original mineral lattice structure of red mud, causing it to generate more internal defects, thereby enabling the dissolution of more active iron, aluminum, and silicon substances.
[0008] In step (3), the addition of silicate solution is to increase the concentration of silicate ions in the entire system. The silicate ions, together with the large amount of phosphate ions generated in step (1), can promote the stability and formation of the amorphous phase of the ferrohydrate mineral phase, preventing it from transforming into stable crystalline phases such as goethite and hematite. The protective effect of freeze-drying is to allow the water in the system to sublimate at low temperature, thereby drying the system and minimizing the phase transformation and crystallization of active components such as active hydroxyl iron oxide and amorphous silica-alumina phase during dehydration, thus maintaining its high reactivity. The purpose of adding calcined alum is to allow it to slowly absorb water inside the slurry to form alum crystal precipitate, which not only disrupts the continuous gel system formed by the silica-alumina phase of the slurry itself, but also allows it to adhere to the active products, keeping them in a stable state.
[0009] Compared with the prior art, the present invention has the following beneficial effects: (1) This invention achieves a decrease in alkalinity and an increase in activity of red mud produced by the Bayer process through a combination strategy of acid synergy and gas synergy.
[0010] (2) By controlling the entire reaction system, this invention guides the formation and dissolution of a large number of active substances such as iron, silicon, and aluminum phases, thereby improving the activity of red mud and solving its low activity problem.
[0011] (3) The present invention achieves the reduction of red mud alkalinity and the improvement of activity by combining chemical reaction, mechanical grinding and gas cavitation corrosion to carry out process synergy treatment.
[0012] (4) The concrete admixture prepared by this invention has the characteristics of high specific surface area and high activity. It can replace part of the cement in equal amounts and be used as a high-quality admixture to improve the particle size distribution and compactness of cementitious materials and improve the overall performance of concrete. At the same time, this method provides a new way for the comprehensive utilization of bulk solid waste red mud and realizes its resource utilization. Detailed Implementation
[0013] The present invention will be described in detail below with reference to the embodiments, but the scope of protection of the present invention is not limited to the following embodiments.
[0014] Example 1 The method for preparing a concrete admixture described in this embodiment is as follows: (1) Take 100 parts red mud, 3 parts oxalic acid, 15 parts phosphoric acid, 0.5 parts dispersant, and 50 parts water, mix and stir to form a paste; grind the paste into powder by wet grinding until the specific surface area is 600 m² / kg to form slurry material A; The red mud mentioned is solid waste red mud produced by the Bayer process. The dispersant is a mixture of polycarboxylate superplasticizer and triethanolamine in a mass ratio of 4:1. When liquid polycarboxylate superplasticizer is used, its solid content is used for calculation.
[0015] (2) Transfer the slurry material A prepared in (1) from the grinding equipment to the stirring equipment, and introduce carbon dioxide gas to remove the air in the stirring equipment; after the carbon dioxide is full, seal the equipment, and under the condition of continuous carbon dioxide introduction, perform ultrasonic vibration at 50kHz and stirring at 120r / min for 10min. (3) Add 5 parts of 25% hydrogen peroxide to the reaction system of step (2), stir evenly, continue to pass carbon dioxide to fill the system, seal the equipment, and react for 1.5 hours under 30kHz ultrasonic vibration. (4) Add 3 parts of silicate solution (concentration of 2 mol / L) to the reaction system of step (3), stir evenly, add 5 parts of calcined alum, stir evenly, transfer to a freeze-drying device for freeze-drying, and then take it out and grind it to a particle size of 800 μm. 2 / kg, to obtain active admixture; The freeze-drying process consists of pre-freezing, sublimation drying, and desorption drying. The pre-freezing parameters are: -50~-60℃ temperature, rate of freezing 2~3℃ / min, and freezing time 8~12h. The sublimation drying parameters are: vacuum degree 10~30Pa, shelf temperature -20~-10℃, and time 24~48h. The desorption drying parameters are: vacuum degree 1~5Pa, shelf temperature 20~30℃, and time 8~12h.
[0016] Example 2 The method for preparing a concrete admixture described in this embodiment is as follows: (1) Take 100 parts red mud, 5 parts oxalic acid, 12 parts phosphoric acid, 2 parts dispersant and 30 parts water, mix and stir to form a paste; grind the paste to a specific surface area of 700 m² / kg to form slurry material A; The red mud mentioned is solid waste red mud produced by the Bayer process. The dispersant is a mixture of polycarboxylate superplasticizer and triethanolamine in a mass ratio of 2:1. When liquid polycarboxylate superplasticizer is used, its solid content is used for calculation. (2) Transfer the slurry material A prepared in (1) from the grinding equipment to the stirring equipment, and introduce carbon dioxide gas to remove the air in the stirring equipment; after the carbon dioxide is full, seal the equipment, and under the condition of continuous carbon dioxide introduction, perform ultrasonic vibration at 30kHz and stirring at 30r / min for 15min. (3) Add 3 parts of 30% hydrogen peroxide to the reaction system of step (2), stir evenly, continue to pass carbon dioxide to fill the system, seal the equipment, and react for 1.2 hours under 50kHz ultrasonic vibration. (4) Add 5 parts of silicic acid solution (concentration of 1 mol / L) to the reaction system of step (3), stir evenly, add 8 parts of calcined alum, stir evenly, transfer to a freeze-drying device for freeze-drying, and then take it out and grind it to a particle size of 700 μm. 2 / kg, to obtain active admixture; The freeze-drying process consists of pre-freezing, sublimation drying, and desorption drying. The pre-freezing parameters are: -50~-60℃ temperature, rate of freezing 2~3℃ / min, and freezing time 8~12h. The sublimation drying parameters are: vacuum degree 10~30Pa, shelf temperature -20~-10℃, and time 24~48h. The desorption drying parameters are: vacuum degree 1~5Pa, shelf temperature 20~30℃, and time 8~12h.
[0017] Example 3 The method for preparing a concrete admixture described in this embodiment is as follows: (1) Take 100 parts red mud, 4 parts oxalic acid, 14 parts phosphoric acid, 1 part dispersant, and 35 parts water, mix and stir to form a paste; grind the paste into powder by wet grinding until the specific surface area is 680 m² / kg to form slurry material A; The red mud mentioned is solid waste red mud produced by the Bayer process. The dispersant is a mixture of polycarboxylate superplasticizer and triethanolamine in a mass ratio of 3:1. When a liquid polycarboxylate superplasticizer is used, its solid content is used for calculation. (2) Transfer the slurry material A prepared in (1) from the grinding equipment to the stirring equipment, and introduce carbon dioxide gas to remove the air in the stirring equipment; after the carbon dioxide is full, seal the equipment, and under the condition of continuous carbon dioxide introduction, perform ultrasonic vibration at 40kHz and stirring at 80r / min for 12min. (3) Add 4 parts of 27.5% hydrogen peroxide to the reaction system of step (2), stir evenly, continue to pass carbon dioxide to fill the system, seal the equipment, and react for 1.3 hours under 40kHz ultrasonic vibration. (4) Add 4 parts of silicic acid solution (concentration of 1.4 mol / L) to the reaction system of step (3), stir evenly, add 6 parts of calcined alum, stir evenly, transfer to a freeze-drying device for freeze-drying, and then take it out and grind it to a particle size of 780 μm. 2 / kg, to obtain active admixture; The freeze-drying process consists of pre-freezing, sublimation drying, and desorption drying. The pre-freezing parameters are: -50~-60℃ temperature, rate of freezing 2~3℃ / min, and freezing time 8~12h. The sublimation drying parameters are: vacuum degree 10~30Pa, shelf temperature -20~-10℃, and time 24~48h. The desorption drying parameters are: vacuum degree 1~5Pa, shelf temperature 20~30℃, and time 8~12h.
[0018] Comparative Example 1 The difference from Example 3 is that only oxalic acid is used, and phosphoric acid is not used.
[0019] Comparative Example 2 The difference from Example 3 is that oxalic acid is not added, and only phosphoric acid is used.
[0020] Comparative Example 3 The difference from Example 3 is that no dispersant mixture of polycarboxylate superplasticizer and triethanolamine is added.
[0021] Comparative Example 4 The difference from Example 3 is that CO2 gas is not introduced in steps (3) and (4).
[0022] Comparative Example 5 The difference from Example 3 is that hydrogen peroxide is not added in step (3).
[0023] Comparative Example 6 The difference from Example 3 is that no silica solution is added in the last step.
[0024] Comparative Example 7 The difference from Example 3 is that the last step is changed to drying in a 105°C forced-air drying oven.
[0025] Comparative Example 8 The difference from Example 3 is that the Bayer red mud was simply wet-milled to a specific surface area of about 780 m² / kg without any chemical treatment.
[0026] Comparative Example 9 The difference from Example 3 is that the Bayer red mud was calcined at 800°C for 2 hours and then mechanically ground to 780 m² / kg.
[0027] Comparative Example 10 The difference from Example 3 is that no calcined alum is added.
[0028] The activity of each example and comparative admixture was tested according to the activity test method of GB / T18046, and the results are shown in Table 1.
[0029] Table 1 Activity of admixtures in each embodiment and comparative example The data in Table 1 shows that: Compared to Example 3, the activity of the admixture in Comparative Example 1 decreased. Due to the lack of a reaction between phosphoric acid and alkaline earth metals in red mud to form calcium phosphate, the alkalinity of the system decreased incompletely, and the synergistic stabilizing effect of calcium phosphate and silicic acid could not be formed. The reaction products contained fewer amorphous substances, and these substances were prone to crystal transformation during later processing, leading to decreased activity.
[0030] Compared to Example 3, the activity of the admixture in Comparative Example 2 decreased. Due to the lack of complexing effect of oxalic acid, the dissolved calcium, aluminum and other metal cations could not be effectively complexed, and easily formed inert crystalline phase precipitates, which coated the surface of unreacted red mud particles, hindering the further dissolution and activation of active substances.
[0031] Compared to Example 3, the activity of the admixture in Comparative Example 3 decreased. This is because the absence of a dispersant led to severe agglomeration of the material during wet milling and reaction, limiting the increase in specific surface area; it also resulted in poor ultrasonic dispersion, uneven reaction, and coarse final product particles with fewer crystal nuclei and active sites. Using a mixture of polycarboxylic acid and triethanolamine in a specific ratio achieved a good dispersion effect.
[0032] Compared to Example 3, the activity of the admixture in Comparative Example 4 decreased. The system lacked the pH buffering, carbonization, and catalytic effects of CO2, leading to the decomposition of hydrogen peroxide in alkaline solutions and reduced oxidation efficiency. Simultaneously, it failed to catalyze the formation of the crucial ferric carbonate / aluminum carbonate intermediates, making it difficult to convert into highly active ferric hydroxide and aluminum hydroxide precipitates, resulting in a significantly worse activation effect.
[0033] Compared with Example 3, the activity of the admixture in Comparative Example 5 decreased. The ferrous iron in the red mud could not be rapidly and fully oxidized to ferric iron, the degree of mineral lattice destruction was low, and the internal defects were insufficient, resulting in a significant reduction in the dissolution of active substances such as iron, aluminum, and silicon, and an incomplete activation process.
[0034] Compared to Example 3, the activity of the admixture in Comparative Example 6 decreased. Silicic acid was added to increase the silicate concentration in the system, enabling it to synergistically maintain the stability of the amorphous phase with phosphate. However, the lack of sufficient silicate ions led to decreased stability of the amorphous phase product during subsequent pH adjustment and drying processes, with some products transforming into more crystalline hydroxides or oxides, resulting in decreased activity.
[0035] Compared to Example 3, the activity of the admixture in Comparative Example 7 decreased. The high-temperature dehydration process caused the highly active amorphous hydrate to dehydrate and undergo a crystal transformation, generating highly crystalline products such as goethite or hematite. These crystalline phases have very low activity, resulting in a decrease in the activity of the red mud.
[0036] Compared to Example 3, the activity of the admixture in Comparative Example 8 decreased. This indicates that simple physical grinding has limited effect on improving the activity of red mud.
[0037] Compared to Example 3, Comparative Example 9 represents a common treatment method for red mud as a cementitious material. It can be seen that the activity of its admixtures has decreased.
[0038] Compared to Example 3, the activity of the admixture in Comparative Example 10 decreased. Calcined alum primarily disrupts the continuous gel system formed by the silica-alumina phase of the slurry through water absorption, crystallization, and precipitation. Simultaneously, it adheres to the active products, maintaining their stability. When calcined alum is lacking, the active gel phase in the admixture agglomerates and becomes unevenly dispersed, affecting its activity.
Claims
1. A method for preparing a concrete admixture, characterized in that, Includes the following steps: (1) Mix red mud, oxalic acid, phosphoric acid, dispersant and water to form a paste, and then place the paste in a grinding equipment for wet grinding to form slurry material A; (2) Transfer the slurry material A obtained in step (1) from the grinding equipment to the stirring equipment, and introduce carbon dioxide gas to remove the air in the stirring equipment; after the carbon dioxide is filled, seal the equipment, and perform ultrasonic vibration and continuous slow stirring reaction under the condition of continuous carbon dioxide introduction. (3) Add hydrogen peroxide to the reaction system of step (2), stir evenly, continue to introduce carbon dioxide until it is full, seal the equipment, and carry out ultrasonic vibration reaction. (4) Add silica solution to the reaction system of step (3), stir evenly, add calcined alum, stir evenly again, transfer to freeze-drying equipment for freeze-drying, and then take out and grind to obtain the active concrete admixture.
2. The method for preparing a concrete admixture according to claim 1, characterized in that, The mass fractions of each raw material component in each step are as follows: 100 portions of red mud 3-5 parts oxalic acid 12-15 parts phosphoric acid Dispersant 0.5~2 parts, 30-50 parts water 3-5 parts hydrogen peroxide 3-5 parts of silicic acid solution Add 5-8 parts of calcined alum; The hydrogen peroxide has a mass concentration of 25-30%; The concentration of the silicic acid solution is 1 mol to 2 mol / L.
3. The method for preparing a concrete admixture according to claim 1, characterized in that, The red mud mentioned in step (1) is solid waste red mud produced by the Bayer process; The dispersant is a mixture of polycarboxylate superplasticizer and triethanolamine in a mass ratio of 2 to 4:
1. When liquid polycarboxylate superplasticizer is used, its solid content is used for calculation.
4. The method for preparing a concrete admixture according to claim 1, characterized in that, In step (1), wet grinding is performed until the specific surface area is 600~700 m² / kg.
5. The method for preparing a concrete admixture according to claim 1, characterized in that, The ultrasonic frequency in step (2) is 30~50kHz, the stirring speed is 30~120r / min, and the reaction time is 10~15min.
6. The method for preparing a concrete admixture according to claim 1, characterized in that, The ultrasonic frequency in step (3) is 30~50kHz and the reaction time is 1.2~1.5h.
7. The method for preparing a concrete admixture according to claim 1, characterized in that, The freeze-drying process described in step (4) consists of pre-freezing, sublimation drying, and desorption drying. The pre-freezing parameters are: -50~-60℃ temperature, rate 2~3℃ / min, and freezing time 8~12h. The sublimation drying parameters are: vacuum degree 10~30Pa, shelf temperature -20~-10℃, and time 24~48h. The desorption drying parameters are: vacuum degree 1~5Pa, shelf temperature 20~30℃, and time 8~12h.
8. The method for preparing a concrete admixture according to claim 1, characterized in that, In step (4), the particles are ground to a size of 700~800 μm. 2 / kg.