A method for preparing cement-based materials using carbide steel slag slurry

Abstract

A method for preparing cement-based materials using carbonated steel slag slurry. During preparation, carbon dioxide is introduced while stirring the steel slag and aqueous solution, and the stirring speed and temperature are controlled to obtain carbonated steel slag slurry. The mass of the added water is calculated according to the CO₂ absorption rate, and all the carbonated slurry, the added water, cement and other materials are mixed and stirred to prepare the cement-based materials. The steel slag used in the cement-based materials is converter steel slag with a particle size of 0-75 μm, and the maximum cement replacement rate can reach 30%. Compared with the uncarbonated steel slag composite cement-based materials, the 28-day strength of the carbonated steel slag composite cement-based materials prepared by the present invention can be increased by up to 15%, solving the problem of poor volume stability of steel slag, improving the utilization rate of steel slag, and simultaneously absorbing 10-16 wt.% of carbon dioxide, having obvious economic benefits and environmental protection value.

Description

Technical Field

[0001] The present invention relates to the field of building materials, and particularly to a method for preparing cement-based materials by using carbonated steel slag slurry. Background Art

[0002] Human activities have generated a large amount of carbon dioxide, leading to the global greenhouse effect. "Carbon peak" and "carbon neutrality" are imperative. Alkaline solid wastes can fix carbon dioxide into stable calcium and magnesium carbonates and are potential raw materials for accelerating carbonation to fix carbon dioxide. As the main alkaline solid waste, steel slag is the main by-product in the process of crude steel smelting, and its emission accounts for about 8% - 15% of the crude steel output. Using steel slag as a raw material for fixing carbon dioxide can not only absorb a large amount of carbon dioxide and relieve the greenhouse effect, but also solve the stability problem of steel slag, making it possible to be widely used.

[0003] There are already various ways of carbonating steel slag at home and abroad. Common carbonation methods include solid carbonation and slurry carbonation. Solid carbonation is to carry out carbonation curing of steel slag in a closed space with a certain carbon dioxide concentration, and slurry carbonation is to make a slurry of steel slag and water according to a certain solid-liquid ratio and introduce carbon dioxide during the stirring process to achieve the purpose of carbonating steel slag. Compared with solid carbonation, slurry carbonation takes less time and has a better calcium carbonate crystal form.

[0004] Currently, the technical research on carbonation of steel slag slurry mainly stays in the stage of using the carbonated steel slag powder, that is, filtering the completely carbonated slurry and then drying it to obtain carbonated steel slag powder, which is used as an auxiliary cementitious material to partially replace cement. However, the filtered solution is not utilized. Discharging and treating it will increase capital investment and energy consumption, bring pressure to the environment, and the filtering and drying treatment costs are relatively high, which is not conducive to industrial promotion. Summary of the Invention

[0005] In order to solve the problems existing in the prior art, the present invention provides a method for preparing cement-based materials by using carbonated steel slag slurry with low cost, low resource consumption, environmental friendliness, simple process and short time period. To achieve the above purpose, the technical solution of the present invention is as follows:

[0006] A method for preparing cement-based materials by using carbonated steel slag slurry, comprising the following steps:

[0007] Step 1: Select converter steel slag treated by grinding, and use a sieve with a pore size of 75 μm to screen out the insufficiently ground particles;

[0008] Step 2: Mix the steel slag and water according to a solid-liquid ratio of 0.15 - 0.45 in an open agitator to obtain a slurry;

[0009] Step 3: Heat the slurry in Step 2, and control the temperature during stirring at 20 - 80°C;

[0010] Step 4: Uniformly introduce carbon dioxide gas into the slurry in Step 3 and maintain high-speed stirring to obtain carbonated steel slag slurry. The carbon dioxide concentration is 10 - 99.99%, the gas flow rate is 1 - 3 L / min, the stirring speed is 800 - 1200 rpm / min, and the stirring time of the steel slag slurry is 40 - 120 min.

[0011] Step 5: Calculate the weight gain of the solid part and the water replenishment mass based on the carbon dioxide absorption amount of the steel slag obtained in Step 4, and replenish water to ensure the proportion of water.

[0012] Step 6: After cooling the slurry in Step 5 to room temperature, mix it with materials such as cement to obtain a cement-based material.

[0013] According to the above scheme, the open stirrer in Step 2 is a glass reactor, the lower part of the reactor is a magnetic stirrer with heating function, and the reactor is equipped with a temperature sensor.

[0014] According to the above scheme, during the carbonization process in Step 4, control the carbon dioxide flow rate introduced through a flow meter, and a gas stone is connected at the outlet of the flow meter to make the carbon dioxide diffusion more uniform.

[0015] According to the above scheme, the carbon dioxide absorption rate of the carbonated steel slag slurry in Step 4 is 10 - 16 wt.%, and the solution pH is 6 - 9.

[0016] According to the above scheme, the calculation formula for the water replenishment mass in Step 5 is:

[0017] m 补水 =(CO 2吸吸 (%)×m 钢渣 +m 固 )×w / c - m 水

[0018] Where CO 2吸收 (%) is the carbon dioxide absorption rate, m 钢渣 is the mass of the incorporated steel slag, m 固 is the total mass of the used cementitious materials (including steel slag and cement, etc.), w / c is the water-cement ratio, and m 水 is the mass of water used for carbonization.

[0019] According to the above scheme, the cement-based material in Step 6 is a composite material with cement and carbonated steel slag as the main cementitious materials, and the proportion of steel slag replacing cement is 0 - 30%, including but not limited to cement paste, cement mortar or concrete.

[0020] The present invention has the following advantages and beneficial effects:

[0021] (1) The method for pre-treating steel slag provided by the present invention uses a slurry carbonization process to treat steel slag. On the one hand, carbon dioxide consumes free magnesium oxide and free calcium oxide in the steel slag, making the soundness of the steel slag meet the standard; on the other hand, nano-calcium carbonate particles exist on the surface and in the solution of the carbonized steel slag. After being mixed with cement, they provide nucleation sites for cement hydration, promote cement hydration, and improve the early strength. It can effectively avoid problems such as long cycle, poor stability, and complex process in the traditional method of disposing steel slag.

[0022] (2) By carbonizing the steel slag slurry for 40 - 120 minutes and directly adding the entire carbonized slurry to the cement, the present invention reduces the filtration and drying costs brought about by only using the carbonized steel slag powder, makes full use of the carbonized solution, reduces pollution emissions, makes the entire process simpler, more efficient, and more environmentally friendly, and promotes the implementation of industrial production.

[0023] (3) The technology of carbonizing steel slag adopted in the present invention can absorb 10 - 16 wt.% of carbon dioxide, realizing the resource utilization of carbon dioxide in the field of building materials, contributing to reducing the carbon emissions in the whole life cycle of building materials, and having significant environmental protection value and application prospects. Description of the Drawings

[0024] Figure 1 (a) is the scanning electron micrograph of the steel slag powder before carbonization, and (b) is the scanning electron micrograph of the steel slag powder after carbonization.

[0025] Figure 2 is the scanning electron micrograph of the residue after evaporation of the filtrate after carbonization. Embodiment

[0026] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below.

[0027] Example 1

[0028] The steel slag selected in this example is the converter steel slag after grinding treatment, and the median particle size is 8.235 μm. Its chemical composition is shown in Table 1:

[0029] Table 1 Chemical composition of steel slag (wt.%)

[0030] CaO <![CDATA[Fe2O3]]> <![CDATA[SiO2]]> MgO MnO <![CDATA[Al2O3]]> <![CDATA[P2O5]]> 42.09 21.72 16.50 6.71 4.83 3.48 2.18 2.49

[0031] This example includes the following steps:

[0032] (1) Use a sieve with a pore size of 75 μm to screen out the particles that are not sufficiently ground.

[0033] (2) 225 g of steel slag and 600 g of water were mixed in a blender at a solid-liquid ratio of 0.375 to obtain a slurry.

[0034] (3) Raise the temperature of the slurry in the stirrer to 38°C and proceed to step (4).

[0035] (4) Carbon dioxide with a concentration of 99.99% was uniformly introduced into the slurry at a flow rate of 2 L / min and a stirring speed of 1000 rpm / min. The carbonization time of the steel slag slurry was 40 min. The slurry temperature was maintained at 40°C ± 2°C during the whole process, and a carbonized steel slag slurry with a carbon dioxide absorption rate of 11.54 wt.% and a solution pH of 8.163 was obtained.

[0036] (5) Based on the carbon dioxide absorption of steel slag of 11.54 wt.%, the water mass is calculated to be 10.39 g. 10.39 g of water is added to the carbonized steel slag slurry to ensure the proportion of water.

[0037] (6) According to the water-cement ratio of 0.4 and the steel slag content of 15%, it is calculated that 1275g of cement should be added. The carbonized steel slag slurry and cement after cooling to room temperature are added to the cement mortar mixer and stirred at low speed for 2 minutes and at high speed for 2 minutes to obtain the clean slurry.

[0038] (7) Place the slurry into the mold and vibrate evenly on a vibration table for 1 minute to form the mold.

[0039] (8) Cover the cement mortar with plastic film and remove the mold after curing for 24 hours in an indoor environment.

[0040] According to the above scheme, the open stirrer in step (2) is a glass reactor, the lower part of the reactor is a magnetic stirrer with a heating function, and a temperature sensor is provided in the reactor.

[0041] According to the above scheme, during the carbonization process in step (4), the flow rate of the introduced carbon dioxide is controlled by a flow meter, and an air stone is connected to the outlet of the flow meter to make the carbon dioxide diffuse more evenly.

[0042] Comparative Example 1:

[0043] The steel slag selected in this comparative example is the same as that in Example 1.

[0044] Compared with Example 1, this comparative example does not include the carbonized steel slag slurry steps (3) (4) (5), and the remaining steps are the same.

[0045] The compressive strength test was performed on the samples of Example 1 and Comparative Example 1, with reference to GB / T17671-1999 "Test method for strength of cement mortar (ISO method)". The test results are shown in Table 2.

[0046] Table 2 Compressive strength test results of Example 1 and Comparative Example 1

[0047] Others Group 1 day (MPa) 3 days (MPa) 7 days (MPa) 13.57 31.73 47.47 64.30 28 days (MPa) 9.20 27.00 39.57 55.90

[0048] It can be seen from the test results of compressive strength that, compared with Comparative Example 1, the strength of Example 1 has been significantly improved. The strength at 1 day and 3 days has increased by 47.50% and 17.52% respectively, and the strength at 7 days and 28 days has increased by 19.96% and 15.03% respectively.

[0049] The volume stability of the samples of Example 1 and Comparative Example 1 was tested. The boiling test was carried out in accordance with GB / T 1346-2001 "Test Methods for Water Requirement of Normal Consistency, Setting Time and Soundness of Cement" to detect the volume stability problem caused by free calcium oxide. When the average value of the increase distance of the two specimens after boiling is not greater than 5.0 mm, it is considered that the soundness is qualified, otherwise it is unqualified. The autoclave test was carried out in accordance with GB / T750-1992 "Test Method for Autoclave Soundness of Cement" to detect the volume stability problem caused by free magnesium oxide. When the autoclave expansion rate is not greater than 0.50%, it is considered that the volume stability is qualified, otherwise it is unqualified. The test results are shown in Table 3.

[0050] Table 3 Volume stability test results of Example 1 and Comparative Example 1

[0051] Example 1 Comparative Example 1 Group Expansion amount by boiling method (mm) Autoclave expansion rate (%) 1.635 0.30 Whether qualified Example 1 6.301 1.30 Yes

[0052] As can be seen from the above table, the expansion of Comparative Example 1 is significantly higher than the standard values of 5.0 mm and 0.50%, while the volume stability test of Example 1 has reached the specification standard.

[0053] Example 2

[0054] The steel slag selected in this example is the converter steel slag after grinding treatment, and the median particle size is 14.588 μm. Its chemical composition is shown in Table 4:

[0055] Table 4 Chemical composition of steel slag (wt.%)

[0056] Comparative Example 1 <![CDATA[Fe2O3]]> <![CDATA[SiO2]]> No CaO <![CDATA[Al2O3]]> <![CDATA[P2O5]]> MgO 45.69 23.42 13.72 4.23 4.78 3.59 1.49 3.08

[0057] The difference between this example and Example 1 is that: the carbonization time was extended to 80 minutes, and a carbonized steel slag slurry with a carbon dioxide absorption rate of 10.87 wt.% and a solution pH of 7.391 was obtained, and the calculated water replenishment mass was 9.78 g.

[0058] Comparative Example 2:

[0059] The difference between this Comparative Example 2 and Comparative Example 1 is that: the steel slag selected in this comparative example is the same as that in Example 2, and the rest of the operation steps are the same as those in Comparative Example 1.

[0060] The compressive strength of the samples of Example 2 and Comparative Example 2 was tested, and the test results are shown in Table 5.

[0061] Table 5 Compressive strength test results of Example 2 and Comparative Example 2

[0062]

[0063]

[0064] It can be seen from the test results of the compressive strength that, compared with Comparative Example 2, the strength of Example 2 was significantly improved. The strength at 1 day and 3 days increased by 57.62% and 26.58% respectively, and the strength at 7 days and 28 days increased by 14.05% and 6.50% respectively.

[0065] The volume stability of the samples of Example 1 and Comparative Example 1 was tested, and the test results are shown in Table 6.

[0066] Table 6 Volume stability test results of Example 2 and Comparative Example 2

[0067] MnO Others Group Expansion amount by boiling method (mm) Autoclave expansion rate (%) 1.704 0.40 Whether qualified Example 2 6.405 1.50 Yes

[0068] As can be seen from the above table, the expansion of Comparative Example 2 was significantly higher than the standard of 5.0 mm and 0.50%, while the volume stability test of Example 2 had reached the specification standard.

[0069] The principle of the present invention is as follows:

[0070] The free calcium oxide (f-CaO) and calcium silicate (C3S and C2S) in the steel slag, and the dissolved calcium ions (Ca 2+ ) are prone to carbonization reaction with carbon dioxide to form nanoscale calcite (as Comparative Example 2 shown), which can provide additional nucleation sites for the hydration of C3S, promote the cement hydration reaction. The products of carbonization and hydration can fill the pores, making the microstructure of the test block more dense and improving the early strength. There are a large amount of magnesium elements in the solution after filtering the carbonized slurry (see Table 7). Scanning electron microscopy analysis was carried out on the solid residue after evaporating the filtrate. It can be seen from No that there are a large number of equidiameter columnar minerals in the residue, with a length of dozens of micrometers, which is MgCO3·3H2O, proving that carbonizing steel slag by the slurry carbonization method can effectively solve the volume stability problem caused by free calcium oxide and free magnesium oxide in the steel slag. During the cement hydration process, the carbonate ions in the carbonized steel slag slurry will react with the aluminate phase in the cement to form calcium aluminate carbonate, which can improve the strength of the specimen.

[0071] Table 7 Concentrations of various elements in the solution after carbonization (mg / L)

[0072] Figure 1 Figure 2 Mg Ca K Si Na Fe 1133.02 583.58 127.22 84.02 9.42 0.76

[0073] The above description of the embodiments is provided to enable those of ordinary skill in the art to understand and use the invention. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative efforts. Therefore, the present invention is not limited to the above embodiments, and all improvements and modifications made by those skilled in the art without departing from the scope of the present invention according to the disclosure of the present invention should be within the protection scope of the present invention.

Claims

1. A method for preparing a cement-based material using a carbide steel slag slurry system, characterized in that It includes the following steps: Step 1: Select the converter steel slag treated by grinding, and use a sieve with a pore size of 75 μm to screen out the insufficiently ground particles; Step 2: Mix the steel slag and water at a solid-liquid ratio of 0.15 - 0.45 in an open stirrer to obtain a slurry; Step 3: Heat the slurry in Step 2, and control the temperature during stirring at 20 - 80 °C; Step 4: Uniformly introduce carbon dioxide gas into the slurry in Step 3 and maintain high-speed stirring to obtain a carbonated steel slag slurry. The carbon dioxide concentration is 10 - 99.99%, the gas flow rate is 1 - 3 L / min, the stirring speed is 800 - 1200 rpm / min, and the stirring time of the steel slag slurry is 40 - 120 min; Step Five: According to the carbon dioxide absorption rate of the steel slag obtained in Step Four, calculate the water replenishment mass through the following formula: m 补水 =(CO 2吸收 (%)×m 钢渣 +m 固 )×w / c - m 水 Among them, CO 2吸收 (%) is the carbon dioxide absorption rate of steel slag, m 钢渣 is the mass of the added steel slag, m 固 is the total mass of the used steel slag and cement, w / c is the water-cement ratio, m 水 is the mass of water used for carbonation; water is replenished according to the calculation results to maintain the proportion of water; Step 6: Cool the steel slag slurry obtained in Step 5 to room temperature and then mix it with cement to obtain a cement-based material.

2. The method for preparing a cement-based material using a steel slag slurry according to claim 1, characterized in that: The carbon dioxide absorption rate of the carbonated steel slag slurry described in Step 4 is 10 - 16 wt.%, and the solution pH is 6 - 9.

3. A method for preparing a cement-based material using a carbide steel slag slurry according to claim 1, characterized in that: The cement-based material described in Step 6 is a composite material with cement and carbonated steel slag as the main cementitious materials. The proportion of steel slag replacing cement is 0 - 30%, and it includes neat cement paste, cement mortar or concrete.

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