Method for preparing concrete admixture by using multi-element solid waste in coordination

Abstract

The application discloses a method for preparing a concrete admixture by using multiple solid wastes in cooperation. The method comprises the following steps: firstly, mixing steel slag, red mud and calcium hydroxide to obtain a mixed product A by means of pulverization; secondly, mixing the mixed product A with water to form a slurry, then adding dilute sulfuric acid to adjust the pH of the system to a range of 9-10.5, and then adding a buffer to mix uniformly to form a slurry B; finally, pouring the slurry B into a sealed stirring container, vacuumizing, then introducing oxygen into the container while stirring until the atmospheric pressure is reached, then heating to 40-60 DEG C, and then performing ultrasonic vibration activation and curing to obtain the concrete admixture. The method realizes the cooperative application of the red mud and the steel slag, improves the activity of the admixture, realizes the resource utilization of the admixture, and provides a new technical means for the resource utilization of bulk solid wastes.

Description

Technical Field

[0001] This invention belongs to the field of industrial solid waste resource utilization and building material preparation, specifically relating to a method for the synergistic preparation of concrete admixtures from multiple solid wastes. Background Technology

[0002] Steel slag is a major solid waste generated during steel smelting, with large emissions and low utilization rates. Its application in concrete is an important direction for resource utilization, but due to its high f-CaO content, it is prone to alkali-aggregate reaction and expansion cracking when used as aggregate, and has poor volume stability when used as an admixture. Furthermore, steel slag has low activity, significantly limiting its dosage in concrete. Red mud is a major strongly alkaline solid waste from the alumina industry, with large reserves. Its use as a cement raw material is an important application, but its high alkali content, large compositional fluctuations, and complex composition make effective control of composition and dosage during cement preparation difficult. Therefore, using it as an admixture is a crucial direction. However, its low activity and often high heavy metal content lead to low utilization rates. Therefore, how to fully and synergistically utilize these two solid wastes is an important direction for achieving the resource utilization of large-scale solid waste. Currently, there are no measures for synergistically utilizing these two solid wastes to prepare concrete admixtures. Summary of the Invention

[0003] Based on the problems existing in the above-mentioned background technology, the present invention proposes a method for the synergistic preparation of concrete admixtures from multiple solid wastes, which realizes the synergistic application of red mud and steel slag, improves the activity of the admixture, realizes its resource utilization, and provides a new technical means for the resource utilization of bulk solid wastes.

[0004] To achieve the above-mentioned objectives, the present invention provides the following technical solution: A method for synergistically preparing concrete admixtures from multiple solid wastes includes the following steps: (1) Mix and grind steel slag, red mud and calcium hydroxide to a mixed product A of not less than 600 m² / kg to ensure that it can be fully activated in the later stage; (2) After mixing the mixed product A obtained in step (1) with water to form a slurry, add dilute sulfuric acid to adjust the pH of the system to the range of 9 to 10.5, then add buffer solution and mix evenly to form slurry B; The buffer solution is a borax-sodium hydroxide buffer solution or a CAPS buffer solution; (3) Pour the slurry B obtained in step (2) into a sealed mixing container, evacuate the container, and then introduce oxygen to atmospheric pressure while stirring. Then, further heat the container to 40~60℃ and perform ultrasonic vibration activation curing for more than 48 hours to obtain activated product C, which is the concrete admixture prepared by this invention. The ultrasonic vibration frequency is 80~100kHz.

[0005] Furthermore, the mass fractions of each raw material component described in this invention are as follows: 100 portions of steel slag 20-40 parts red mud 5-10 parts calcium hydroxide, 30-50 parts water 14-16 portions of buffer solution.

[0006] Furthermore, the red mud mentioned in step (1) is red mud produced by the Bayer process.

[0007] Furthermore, the pH value of the borax-sodium hydroxide buffer solution in step (2) is controlled between 9.3 and 10.5; The pH value of the CAPS buffer solution is controlled between 9 and 10.

[0008] Furthermore, the method of using the concrete admixture of the present invention includes: using the concrete admixture directly as activated steel slag slurry, or using it as activated steel slag powder after drying treatment.

[0009] Furthermore, the prepared active concrete admixture composed of steel slag and red mud can replace 20% to 40% of cement when used in concrete. If it is used as an activated steel slag slurry, the water content needs to be calculated and deducted.

[0010] The active admixture prepared by this invention can be used in engineering scenarios that require high impermeability, high corrosion resistance, or heavy metal curing function.

[0011] This invention primarily focuses on the leaching reaction of iron oxides. It promotes the conversion of divalent iron oxide to trivalent iron oxide through an oxygen-rich environment, thereby increasing internal defects and facilitating the leaching of calcium-silica-alumina active substances, thus enhancing overall activity. Furthermore, the generated trivalent iron oxide can form ferrohydrate under oxygen-rich and stable pH conditions. Ferrohydrate is a nanoscale, amorphous, hydrous iron oxide with a large specific surface area and abundant surface hydroxyl groups, exhibiting strong adsorption and solidification capabilities and activity for heavy metal ions. This invention generates ferrohydrate in situ in steel slag and red mud, simultaneously enhancing its chemical activity and cementing properties, thereby improving its adsorption and solidification capacity for heavy metals in red mud. Currently, existing technologies lack effective methods for the directional induction of ferrohydrate formation in steel slag systems. Simultaneously, the activated steel slag and red mud are co-processed to address the resource utilization of both waste materials. Moreover, current activation systems primarily rely on the leaching of calcium-silica-alumina active oxides, neglecting the impact of iron oxide leaching on activation efficiency.

[0012] Compared with the prior art, the present invention has the following beneficial effects: This invention provides a solution to the problems of low cementitious activity, poor volume stability, and difficulty in utilizing the high alkalinity of red mud caused by single steel slag.

[0013] (1) Based on the mechanical grinding of the slag-red mud system, this invention induces the in-situ generation of nano-ferroalloys from the iron phase components in the steel slag-red mud activation system by controlling the oxidation conditions and pH value, while simultaneously generating a large amount of silicon-aluminum active products to form a composite admixture. This method not only significantly stimulates the cementitious and chemical activity of steel slag, but also achieves efficient disposal and alkalinity resource utilization of red mud. The resulting composite admixture has excellent mechanical properties, volume stability, and heavy metal solidification function, and can replace 20%-40% of cement in equal amounts.

[0014] (2) Overall, firstly, the present invention achieves synergistic activation of slag and red mud, and improves the activity of admixtures; secondly, the present invention endows admixtures with the property of solidifying heavy metals, and improves the ability of concrete to solidify heavy metals; thirdly, the present invention provides a new technical means for large-scale disposal of steel slag and red mud, realizes resource utilization, reduces concrete production costs, and has high added value. Detailed Implementation

[0015] The present invention will be further described below with reference to specific embodiments.

[0016] Example 1 A method for synergistic preparation of concrete admixtures from multiple solid wastes, the preparation method is as follows: (1) Mix and grind 100 parts steel slag, 20 parts red mud and 10 parts calcium hydroxide to 600 m² / kg to ensure that they can be fully activated in the later stage to obtain mixed product A; (2) Mix mixture A with 50 parts of water to form a slurry, add dilute sulfuric acid to adjust the pH of the system to 9, and add 14 parts of borax-sodium hydroxide buffer solution with a pH of 9.3 to form slurry B; (3) Pour slurry B into a sealed mixing container, evacuate the container, and then introduce oxygen to atmospheric pressure while stirring. Further heat the container to 60°C and perform ultrasonic vibration activation and curing for 48 hours. The ultrasonic vibration frequency is 100kHz to obtain activated product C. (4) The product cured in step (3) is used directly as activated steel slag slurry.

[0017] Example 2 A method for synergistically preparing concrete admixtures from multiple solid wastes includes the following steps: (1) Mix and grind 100 parts steel slag, 40 parts red mud and 5 parts calcium hydroxide to 680 m² / kg to ensure that they can be fully activated in the later stage to obtain mixed product A; (2) Mix mixture A with 30 parts of water to form a slurry, add dilute sulfuric acid to adjust the pH of the system to within the range of 10, and then add 16 parts of CAPS buffer with a pH of 10 to form slurry B; (3) Pour slurry B into a sealed mixing container, evacuate the container, and then introduce oxygen to atmospheric pressure while stirring. Further heat the container to 40°C and perform ultrasonic vibration activation and curing for 72 hours. The ultrasonic vibration frequency is 80kHz. Activated product C is obtained. (4) The product cured in step (3) is dried to make activated steel slag powder.

[0018] Example 3 A method for synergistically preparing concrete admixtures from multiple solid wastes includes the following steps: (1) Mix and grind 100 parts steel slag, 30 parts red mud and 8 parts calcium hydroxide to 720 m² / kg to ensure that they can be fully activated in the later stage to obtain mixed product A; (2) After mixing mixture A with 40 parts of water to form a slurry, dilute sulfuric acid is added to adjust the pH of the system to within the range of 10.5. Then, 15 parts of borax-sodium hydroxide buffer solution with a pH of 10.5 are added to form slurry B. (3) Pour slurry B into a sealed mixing container, evacuate the container, and then introduce oxygen to atmospheric pressure while stirring. Further heat the container to 50°C and perform ultrasonic vibration activation and curing for 54 hours. The ultrasonic vibration frequency is 98kHz. Activated product C is obtained. (4) The product cured in step (3) is used directly as activated steel slag slurry.

[0019] Comparative Example 1 Compared to Example 3, only 130 parts of steel slag were used, and no red mud was used.

[0020] Comparative Example 2 Compared to Example 3, only 130 parts of red mud were used, and steel slag was not used.

[0021] Comparative Example 3 Compared to Example 3, steel slag and red mud were mixed in a 1:1 ratio, with each accounting for 65 parts.

[0022] Comparative Example 4 Compared to Example 3, no calcium hydroxide was added.

[0023] Comparative Example 5 Compared to Example 3, pH was not controlled.

[0024] Comparative Example 6 Compared to Example 3, no buffer solution was added.

[0025] Comparative Example 7 Compared to Example 3, oxygen was introduced without creating a vacuum.

[0026] Comparative Example 8 Compared to Example 3, ultrasonic cavitation was not performed; instead, curing was carried out at room temperature.

[0027] Comparative Example 9 Compared to Example 3, the ultrasonic frequency was 50 kHz.

[0028] Comparative Example 10 Compared to Example 3, the temperature was kept at 28°C and not increased to 50°C.

[0029] Comparative Example 11 Compared to Example 3, the only difference is that 100 parts of steel slag and 30 parts of red mud are mixed and ground to 720 m² / kg.

[0030] The admixtures prepared in the above embodiments and comparative examples were used to replace 30% of the cement and incorporated into the reference concrete. The mix proportions of the reference concrete are shown in Table 1.

[0031] Table 1. Concrete Standard Mix Proportion The admixture prepared above was used to replace cement at a dosage of 30% to form a cementitious material, which was then added to the concrete. The properties of the concrete are shown in Table 2. The compressive strength was tested according to the provisions of GB / T 50081 "Standard for Test Methods of Physical and Mechanical Properties of Concrete"; the electrical flux was tested according to GB / T 50082 "Standard for Test Methods of Long-Term Performance and Durability of Concrete"; and the heavy metal leaching was tested according to HJ557 "Leaching Toxicity of Solid Waste - Horizontal Vibration Method".

[0032] Table 2 Concrete Properties As can be seen from the comparison of the examples and the benchmark concrete in Table 2, the 7-day and 28-day compressive strengths of the concrete with the admixture prepared according to the present invention did not decrease, and the 7-day compressive strength was improved to a certain extent, while the 28-day compressive strength was also slightly improved. This indicates that the iron and aluminum mineral phases in the mineral admixtures contribute to the formation of early strength and are beneficial to the improvement of concrete density and the ability to solidify heavy metals.

[0033] Comparing Example 3 and Comparative Example 1, it can be seen that the compressive strength decreased slightly, the electrical flux increased, and the heavy metal solidification ability weakened. Red mud contains a large amount of iron and aluminum oxides, which increases the formation of active ferrohydrates and aluminum oxide active products. This is beneficial for the formation of hydrated iron and aluminum oxides in cement hydration products, improving the density and structural stability of concrete structures. Without red mud, only iron oxides from steel slag form ferrohydrate active products, but the amount is insufficient, and the formation of aluminum phase active minerals is lacking, thus weakening the effect on improving concrete performance.

[0034] Comparing Example 3 and Comparative Example 2, it can be seen that the compressive strength decreased slightly, the electrical flux increased, and the heavy metal solidification ability weakened. Steel slag contains abundant iron-phase minerals, which facilitates the formation of ferrohydrate products, increasing the heavy metal adsorption capacity and the dissolution of active products in the silica-alumina phase. The lack of an iron phase reduces the formation of these active products, resulting in a decrease in the corresponding hydration products in the concrete, weakening its compactness and binding properties, and ultimately reducing its overall performance.

[0035] Comparing Example 3 and Comparative Example 3, it can be seen that the compressive strength decreased slightly, the electrical flux increased, and the heavy metal solidification ability weakened. This indicates that when red mud and steel slag are mixed in a certain proportion, the ratio of iron and aluminum active products in the generated active products can be coordinated, resulting in the formation of a dense iron-aluminum gel in the concrete hydration products. This helps to improve the compactness of the concrete and enhance its corrosion resistance and mechanical properties. When the ratio of the two is different, it will affect the type of hydration products generated, and the improving effect on the concrete will be weakened. This illustrates the importance of controlling the ratio of red mud and steel slag.

[0036] Comparing Example 3 and Comparative Example 4, it can be seen that the compressive strength decreased, the electrical flux increased, and the heavy metal curing ability weakened. Calcium hydroxide mainly plays a role in activating the pre-dissolution of active substances in the early stage; its lack of participation in the reaction affects the formation of iron and aluminum active oxides in the later stage.

[0037] Comparing Example 3 and Comparative Example 5, it can be seen that the concrete strength decreases and the heavy metal adsorption capacity weakens. Without pH control, the generated active ferrohydrate becomes unstable, crystallizes and precipitates, losing its hydration activity, thus leading to a decrease in concrete strength and a weakened heavy metal adsorption capacity.

[0038] Comparing Example 3 and Comparative Example 6, it can be seen that the concrete strength decreases and the heavy metal adsorption capacity weakens. Similar to Comparative Example 5, without the addition of buffer solution, the alkaline substances in the red mud will release a large amount of alkaline substances during the activation process, increasing the pH of the slurry, causing the generated ferrous ore products to crystallize and precipitate, losing their adsorption and hydration capabilities.

[0039] Comparing Example 3 and Comparative Example 7, it can be seen that the concrete strength decreases, the electrical flux increases, and the heavy metal adsorption capacity weakens. Vacuuming and introducing oxygen while stirring are used to create an oxygen-rich environment. Under these conditions, ferrous ions in the minerals are easily oxidized and detached from the ore, increasing reaction and activation efficiency. When oxygen is not introduced, the oxidation of ferrous ions in the minerals is extremely slow, resulting in a significant reduction in activation efficiency, which in turn reduces the amount of active products generated and diminishes the improvement effect on the concrete.

[0040] Comparing Example 3 and Comparative Example 8, it can be seen that the concrete strength decreases, the electrical flux increases, and the heavy metal adsorption capacity weakens. This indicates that ultrasonic cavitation can significantly increase the excitation effect on ferrous ions, thereby increasing the dissolution of active substances. Without ultrasonic cavitation, the activation efficiency and activation products decrease significantly.

[0041] Comparing Example 3 and Comparative Example 9, it can be seen that the concrete strength decreases, the electrical flux increases, and the heavy metal adsorption capacity weakens. This indicates that at lower ultrasonic cavitation frequencies, the excitation efficiency is poor, and the generation of active products decreases, making it necessary to control the ultrasonic frequency.

[0042] Comparing Example 3 and Comparative Example 10, it can be seen that the concrete strength decreased, the electrical flux increased, and the heavy metal adsorption capacity weakened. This indicates that increasing the temperature can increase the reaction rate and is beneficial to the formation of active products.

[0043] Comparing Example 3 and Comparative Example 11, it can be seen that without activation treatment, the concrete strength, electrical flux, and heavy metal curing ability are significantly reduced, which fully demonstrates the effectiveness of the activation of the present invention.

Claims

1. A method for synergistic preparation of concrete admixtures from multiple solid wastes, characterized in that, Includes the following steps: (1) Steel slag, red mud and calcium hydroxide are mixed and ground to obtain mixed product A; (2) After mixing the mixed product A obtained in step (1) with water to form a slurry, add dilute sulfuric acid to adjust the pH of the system to the range of 9 to 10.5, then add buffer solution and mix evenly to form slurry B; The buffer solution is a borax-sodium hydroxide buffer solution or a CAPS buffer solution; (3) Pour the slurry B obtained in step (2) into a sealed mixing container, evacuate the container, and then introduce oxygen to atmospheric pressure while stirring. After that, heat the container to 40~60℃ and perform ultrasonic vibration activation curing to obtain activated product C, which is the concrete admixture.

2. The method for co-preparing concrete admixtures from multiple solid wastes according to claim 1, characterized in that, In step (1), the powder is ground to a density of not less than 600 m² / kg.

3. The method for co-preparing concrete admixtures from multiple solid wastes according to claim 1, characterized in that, The red mud mentioned in step (1) is red mud produced by the Bayer process.

4. The method for co-preparing concrete admixtures from multiple solid wastes according to claim 1, characterized in that, In step (2), the pH value of the borax-sodium hydroxide buffer solution is controlled between 9.3 and 10.5; The pH value of the CAPS buffer solution is controlled between 9 and 10.

5. The method for co-preparing concrete admixtures from multiple solid wastes according to claim 1, characterized in that, The ultrasonic vibration activation and curing time in step (3) is more than 48 hours.

6. The method for co-preparing concrete admixtures from multiple solid wastes according to claim 1, characterized in that, The ultrasonic vibration frequency in step (3) is 80~100kHz.

7. The method for co-preparing concrete admixtures from multiple solid wastes according to claim 1, characterized in that, The mass fractions of each raw material component in each step are as follows: 100 portions of steel slag 20-40 parts red mud 5-10 parts calcium hydroxide, 30-50 parts water 14-16 portions of buffer solution.

8. A method for using a concrete admixture prepared by the method according to any one of claims 1 to 7, characterized in that, The concrete admixture can be used directly as activated steel slag slurry, or it can be dried and made into activated steel slag powder for use.

9. The method of use according to claim 8, characterized in that, When the concrete admixture is used in concrete, it replaces 20% to 40% of the cement. If it is used as activated steel slag slurry, the water content must be calculated and deducted.

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