Method for simultaneously producing light calcium carbonate and cement raw material from steel slag

Abstract

The application discloses a method for simultaneously preparing light calcium carbonate and cement raw material from steel slag, which comprises the following steps: (1) crushing the steel slag, adding acetic acid solution for acidification, and preparing acidified steel slag; (2) performing microwave activation treatment on the acidified steel slag, and preparing activated steel slag; (3) performing air quenching on the activated steel slag, then diluting the activated steel slag with water to a mass ratio of leaching solution to steel slag of 3-10:1, adjusting pH to 2.0-2.5, stirring for 10-90 min, and filtering to obtain a calcium-containing filtrate and tailings; and (4) introducing CO2 gas into the calcium-containing filtrate, stirring at 40-70 DEG C for 30-120 min, adjusting pH to 7-8, and filtering to obtain light calcium carbonate and filtrate. The method solves the technical problems of resource utilization of steel slag waste and carbon dioxide.

Description

Technical Field

[0001] This invention belongs to the field of waste resource utilization technology, specifically relating to a method for simultaneously preparing lightweight calcium carbonate and cement raw materials from steel slag. Technical Background

[0002] While the main components of steel slag are suitable as cement raw materials, the presence of free calcium oxide significantly reduces its stability when used as a building material. Therefore, solidifying CO2 from steel slag to reduce carbon emissions and producing high-value-added lightweight calcium carbonate and cement raw materials not only achieves the effect of "treating waste with waste" but also realizes the effective utilization of secondary resources.

[0003] Common methods for solidifying CO2 with steel slag include dry and wet carbonation methods. Dry carbonation involves the direct reaction of steel slag with carbon dioxide. Patent CN101269920A discloses a method for carbonation treatment of steel slag, in which steel slag with a particle size ≤15mm reacts with CO2 gas for 2–12 hours in a fluidized bed reactor at 350–800℃ and 0.1–3.6 atm. This invention completes the carbonation reaction in one step, and the process is simple, but it is carried out under high temperature and pressure, resulting in high energy consumption and poor economic efficiency.

[0004] The wet carbonation method first leaches calcium and magnesium ions from steel slag, then introduces carbon dioxide to generate carbonate products. These products have high purity and can be used in the production of chemical raw materials. Patent CN104828850A discloses a method for producing high-purity light calcium carbonate from steel slag. This invention involves finely grinding the steel slag to 40μm, extracting calcium oxide from the slag using 0.5% acetic acid, adjusting the pH with alkali, filtering, clarifying, and then introducing carbon dioxide gas from steel plant flue gas for carbonation, thereby producing high-purity light calcium carbonate. Furthermore, the reduced calcium oxide content in the steel slag allows it to be used as a filler in cement-based products. However, this method requires fine grinding, resulting in high energy consumption, a high solid-liquid ratio of 1:200, and high water consumption. The leachate is not recycled, posing a risk of secondary pollution. Patent CN116462217A discloses a method for producing calcium carbonate from steel slag. After finely grinding the steel slag, a solution of ammonium chloride and ammonium nitrate is used for stirring and leaching, followed by solid-liquid separation by settling. Carbon dioxide gas is then introduced for a carbonation reaction to obtain calcium carbonate. This method allows for the recycling of the leaching agent and waste liquid, making it environmentally friendly. However, it still requires finely grinding the steel slag to 100μm (0.1mm), increasing production costs. Patent CN 105197975A discloses a method for preparing light calcium carbonate from converter steel slag. After finely grinding the steel slag, it is mixed with a large amount of NH4Cl solution, and microwave-assisted leaching is used. After filtration, a mixture of CO2 and air is introduced to obtain calcium carbonate. This method has a high leaching rate, simple process, and reusable ammonium chloride solution. However, finely grinding the steel slag to a particle size <150μm results in high grinding energy consumption, increasing production costs. Summary of the Invention

[0005] The purpose of this invention is to provide a method for simultaneously preparing lightweight calcium carbonate and cement raw materials from steel slag, which can effectively solve the problems of steel slag waste and large-scale carbon dioxide emissions.

[0006] To achieve the above objectives, the technical solution provided by the present invention is as follows:

[0007] A method for simultaneously preparing lightweight calcium carbonate and cement raw materials from steel slag includes the following steps:

[0008] (1) Crush the steel slag, add acetic acid solution to acidify it, and make acidified steel slag;

[0009] (2) The acidified steel slag is subjected to microwave activation treatment to produce activated steel slag;

[0010] (3) The activated steel slag is gas quenched and cooled, diluted with water to a mass ratio of leaching solution to steel slag of 3 to 10:1, and the pH is adjusted to 2.0 to 2.5. The mixture is stirred for 10 to 90 min and filtered to obtain calcium-containing filtrate and tailings.

[0011] (4) Introduce CO2 gas into the calcium-containing filtrate, stir at 40-70℃ for 30-120 min, adjust pH to 7-8, and filter to obtain light calcium carbonate and filtrate.

[0012] Furthermore, the main components and mass percentages of the steel slag described in this invention are CaO: 40%–50%, MgO: 5%–15%, SiO2: 10%–20%, Al2O3: 1%–5%, FeO: 10%–20%, and MnO: 1%–5%.

[0013] Furthermore, the particle size of the steel slag after crushing in step (1) of the present invention is 5 to 50 mm.

[0014] Furthermore, the acetic acid solution in step (1) of the present invention has a mass concentration of 30-70% and is prepared using industrial acetic acid; the mass ratio of the steel slag to the acetic acid solution is 1-3:1.

[0015] Furthermore, the acidification temperature in step (1) of the present invention is 40-80°C, and the acidification time is 30-90 min.

[0016] Furthermore, in step (2) of the present invention, the microwave frequency during microwave activation is 2435-2465MHz, and the activation time is 30-60min.

[0017] Furthermore, in step (3) of the present invention, the gas quenching is performed using air, with a quenching pressure of 0.2 to 0.5 MPa and a quenching time of 10 to 30 min;

[0018] Furthermore, the free calcium oxide content in the tailings of step (3) of the present invention is less than 0.5%, and the calcium-containing cementitious component is relatively high, so it can be used as a cement raw material.

[0019] Furthermore, the CO2 gas mentioned in step (4) of the present invention is steel plant tail gas, and the CO2 concentration in the steel plant tail gas is 15-45%.

[0020] Furthermore, the filtrate produced in step (4) of the present invention can be adjusted to pH=2 with nitric acid and then reused in the acetic acid acidification in step (1).

[0021] In step (3) of this invention, the leaching rate of calcium ions in the calcium-containing filtrate is greater than 60%;

[0022] The whiteness of the light calcium carbonate in step (4) of this invention is above 95.

[0023] This invention has the following advantages and positive effects:

[0024] (1) High-concentration acetic acid acidification expands the cracks in steel slag, promoting the dissolution of calcium-containing components, especially free calcium oxide. The phase containing free calcium oxide is the weakest part of steel slag. The thermal effect, cavitation effect, and mechanical effect generated by microwave strengthening treatment further improve the reactivity of steel slag. By activating steel slag through air quenching, the damage healing process of steel slag can be interrupted, effectively refining steel slag minerals, further improving the calcium leaching rate, and oxidizing ferrous acetate to ferric acetate, which then produces ferric hydroxide after hydrolysis, reducing interference with the subsequent carbonization process. The combination of acetic acid acidification-microwave activation-air quenching makes this process less demanding on steel slag particle size, reducing the high energy consumption cost required for fine grinding.

[0025] (2) This process uses a high concentration of acetic acid solution with a small amount of water, which effectively saves water resources; the slurry produced by the carbonation reaction is returned to the front-end step, and the system is circulated internally, avoiding environmental pollution; the free calcium oxide content in the tailings is extremely low and the calcium-containing cementitious components are high, making it suitable as a cement raw material; the process is simple to operate and the calcium carbonate product has high purity, which effectively solves the technical problems of steel slag waste and carbon dioxide resource utilization. Attached Figure Description

[0026] Figure 1 A schematic diagram of the process for simultaneously preparing lightweight calcium carbonate and cement raw materials from steel slag, provided by the present invention.

[0027] Figure 2 The image shows the XRD pattern of the light calcium carbonate prepared in Example 1. Implementation

[0028] The technical solution of the present invention will be further described in detail below through specific embodiments and in conjunction with the accompanying drawings. Example 1

[0029] The main components and their mass percentages of the steel slag in this embodiment are CaO: 44%, MgO: 12%, SiO2: 13%, Al2O3: 3%, FeO: 12%, and MnO: 4%.

[0030] The process flow for simultaneously preparing lightweight calcium carbonate and cement raw materials from steel slag is as follows: Figure 1 As shown, the details are as follows:

[0031] (1) Crush the steel slag to a particle size of P 80 =20.3 mm, add 45% acetic acid solution to acidify, to prepare acidified steel slag; the mass ratio of steel slag to acetic acid solution is 3:1; the acidification temperature is 60℃; the acidification time is 30min.

[0032] (2) The acidified steel slag was microwave activated to produce activated steel slag; the microwave frequency during microwave activation was 2435MHz, the microwave activation time was 60min, and the temperature of the steel slag after microwave activation was 300℃.

[0033] (3) The activated steel slag was air-quenched for 10 min at a pressure of 0.5 MPa; water was added to dilute it to a mass ratio of leaching solution to steel slag of 3:1, and pH was adjusted to 2. The mixture was stirred and reacted for 90 min. The filtrate and tailings were obtained by filtration. The free calcium oxide content in the tailings was 0.2%, and the calcium-containing cementitious component was 19.13%, which was used as cement raw material.

[0034] (4) Introduce CO2 gas into the calcium-containing filtrate. The CO2 gas used is the tail gas of the steel plant. The CO2 concentration in the tail gas is 45%. Stir at 60°C for 30 minutes, adjust pH=8, and filter to obtain light calcium carbonate and filtrate. Add nitric acid to the filtrate to adjust pH=2, and use it in step (1) acetic acid acidification.

[0035] In this embodiment, the calcium leaching rate in the calcium-containing filtrate obtained in step (3) is 70.42%.

[0036] Using the same minerals, acidified steel slag was directly subjected to air quenching without microwave activation. Under the same conditions, a comparative experiment was conducted, and the calcium leaching rate was 58.59%.

[0037] Using the same minerals, acidified steel slag was directly activated by microwave without air quenching. Under the same conditions, a comparative experiment was conducted, and the calcium leaching rate was 63.61%.

[0038] The light calcium carbonate prepared in this embodiment has a purity of 95.7% and a whiteness of 96; the XRD pattern of the light calcium carbonate is shown below. Figure 2 ,Depend on Figure 2 It can be seen that its product is calcium carbonate with high purity. Example 2

[0039] The main components and mass percentages of the steel slag in this embodiment are CaO: 50%, MgO: 5%, SiO2: 20%, Al2O3: 1%, FeO: 10%, and MnO: 1%.

[0040] The method for simultaneously preparing lightweight calcium carbonate and cement raw materials from steel slag is the same as in Example 1, except that:

[0041] (1) Crush the steel slag to a particle size of P 80 =15.0 mm, acetic acid solution mass concentration 70%; steel slag mass to acetic acid solution mass ratio 1:1; acidification temperature 80℃; acidification time 90min.

[0042] (2) The microwave frequency during microwave activation treatment was 2450MHz, the microwave activation time was 40min, and the temperature of the steel slag after microwave activation was 250℃.

[0043] (3) The activated steel slag was air-quenched for 30 min at a pressure of 0.2 MPa; water was added to dilute it to a mass ratio of 10 to 2.5, and the pH was adjusted to 2.5. The stirring time was 10 min. The free calcium oxide content in the tailings was 0.2%, and the calcium-containing cementitious component was 20.79%.

[0044] (4) Introduce CO2 with a concentration of 15%, stir at 40°C for 120 min, and adjust pH to 7.5.

[0045] In this embodiment, the calcium leaching rate in the calcium-containing filtrate obtained in step (3) is 73.08%.

[0046] Using the same minerals, acidified steel slag was directly subjected to air quenching without microwave activation, and other conditions were kept the same. A comparative experiment was conducted, and the calcium leaching rate was 60.17%.

[0047] Using the same minerals, acidified steel slag was directly activated by microwave without air quenching and other conditions were the same. A comparative experiment was conducted, and the calcium leaching rate was 65.33%.

[0048] The light calcium carbonate prepared in this embodiment has a purity of 95.1% and a whiteness of 97. Example 3

[0049] The main components and their mass percentages of the steel slag in this embodiment are CaO: 40%, MgO: 15%, SiO2: 10%, Al2O3: 5%, FeO: 20%, and MnO: 5%.

[0050] The method for simultaneously preparing lightweight calcium carbonate and cement raw materials from steel slag is the same as in Example 1, except that:

[0051] (1) Crush the steel slag to a particle size of P 80 =35.9 mm, acetic acid solution mass concentration 30%; steel slag mass to acetic acid solution mass ratio 2:1; acidification temperature 40℃; acidification time 60min;

[0052] (2) The microwave frequency during microwave activation treatment was 2465MHz, the microwave activation time was 30min, and the temperature of the steel slag after microwave activation was 200℃.

[0053] (3) The activated steel slag was air-quenched for 20 min at a pressure of 0.4 MPa; water was added to dilute the solution to a mass ratio of 7:1 to steel slag, pH was adjusted to 2.3, and stirring was performed for 60 min; the free calcium oxide content in the tailings was 0.3%, and the calcium-containing cementitious component was 17.74%.

[0054] (4) Introduce CO2 with a concentration of 30%, stir at 70°C for 90 minutes, and adjust the pH to 7.

[0055] In this embodiment, the calcium leaching rate in the calcium-containing filtrate obtained in step (3) is 68.61%.

[0056] Using the same minerals, acidified steel slag was directly subjected to air quenching without microwave activation. Under the same conditions, a comparative experiment was conducted, and the calcium leaching rate was 59.95%.

[0057] Using the same minerals, acidified steel slag was directly activated by microwave without air quenching. Under the same conditions, a comparative experiment was conducted, and the calcium leaching rate was 60.46%.

[0058] The light calcium carbonate prepared in this embodiment has a purity of 94.1% and a whiteness of 95.

Claims

1. A method for simultaneously preparing lightweight calcium carbonate and cement raw materials from steel slag, characterized in that, Includes the following steps: (1) Crush the steel slag, add acetic acid solution to acidify it, and make acidified steel slag; (2) The acidified steel slag is subjected to microwave activation treatment to produce activated steel slag; (3) The activated steel slag is gas quenched and then diluted with water to a mass ratio of leaching solution to steel slag of 3 to 10:

1. The pH is adjusted to 2.0 to 2.5, stirred for 10 to 90 min, and filtered to obtain calcium-containing filtrate and tailings. (4) Introduce CO2 gas into the calcium-containing filtrate, stir at 40-70℃ for 30-120 min, adjust pH to 7-8, and filter to obtain light calcium carbonate and filtrate.

2. The method for simultaneously preparing lightweight calcium carbonate and cement raw materials from steel slag according to claim 1, characterized in that, The main components and their mass percentages of the steel slag are as follows: CaO: 40%–50%, MgO: 5%–15%, SiO2: 10%–20%, Al2O3: 1%–5%, FeO: 10%–20%, and MnO: 1%–5%.

3. The method for simultaneously preparing lightweight calcium carbonate and cement raw materials from steel slag according to claim 1, characterized in that, The steel slag in step (1) has a particle size of 5-50 mm after crushing.

4. The method for simultaneously preparing lightweight calcium carbonate and cement raw materials from steel slag according to claim 1, characterized in that, The mass concentration of the acetic acid solution in step (1) is 30-70%; the mass ratio of the steel slag to the acetic acid solution is 1-3:

1.

5. The method for simultaneously preparing lightweight calcium carbonate and cement raw materials from steel slag according to claim 1, characterized in that, The acidification temperature in step (1) is 40-80℃ and the acidification time is 30-90min.

6. The method for simultaneously preparing lightweight calcium carbonate and cement raw materials from steel slag according to claim 1, characterized in that, In step (2), the microwave frequency during microwave activation is 2435–2465 MHz, and the activation time is 30–60 min.

7. The method for simultaneously preparing lightweight calcium carbonate and cement raw materials from steel slag according to claim 1, characterized in that, The gas quenching in step (3) uses air, with a quenching pressure of 0.2 to 0.5 MPa and a quenching time of 10 to 30 minutes.

8. The method for simultaneously preparing lightweight calcium carbonate and cement raw materials from steel slag according to claim 1, characterized in that, The CO2 gas used in step (4) is steel plant tail gas, and the CO2 concentration in the steel plant tail gas is 15-45%.

9. The method for simultaneously preparing lightweight calcium carbonate and cement raw materials from steel slag according to claim 1, characterized in that, The filtrate in step (4) is adjusted to pH 2 by adding acid and then returned to the acidification process described in step (1) by adding acetic acid solution.

10. The method for simultaneously preparing lightweight calcium carbonate and cement raw materials from steel slag according to claim 1, characterized in that, The light calcium carbonate described in step (4) has a whiteness of 95 or higher.

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