Cement clinker based on composite tailings and steel slag and method for its production

Abstract

The application discloses a cement clinker based on composite tailings and steel slag and a preparation method thereof. The cement clinker comprises the following raw materials in parts by weight: limestone 68.0-75.0 parts, lead-zinc tailings 10.5-20.7 parts, granite tailings 5.1-6.1 parts and steel slag 5.2-12.5 parts. The mass percentage of tetracalcium aluminoferrite in the cement clinker is more than 20 wt%, and the mass percentage of tricalcium silicate is less than 50 wt%. The preparation method comprises the following steps: weighing the raw materials according to the weight ratio, ball milling, drying, sieving, loading into a tablet press mold and pressing into round tablets, ladder heating the round tablets to 1350-1375 DEG C, keeping warm, obtaining the sintered cement clinker, rapidly cooling to below 300 DEG C, and grinding to below 200 mesh using a vibration mill. The application helps to reduce the accumulation of tailings and steel slag resources, effectively improves the comprehensive utilization rate of aluminosilicate industrial solid waste resources and the use range in the building material field.

Description

Technical Field

[0001] This invention relates to a method for utilizing solid waste, specifically a cement clinker based on composite tailings and steel slag and its preparation method. Background Technology

[0002] High-iron, low-calcium phase cement refers to a green, low-carbon, medium- and low-heat silicate cement with a tetracalcium aluminoferrite content higher than 18 wt% and a tricalcium silicate content lower than 50 wt%. Its average calcination temperature is around 1350℃. During cement hydration, the rate and amount of heat released are relatively low, resulting in a dense structure of hydration products that effectively seal in heavy metals and other harmful elements. Currently, the raw materials for silicate cement production, besides ferrous raw materials, are primarily naturally mined limestone, siliceous rocks, and aluminosilicate rocks, among other natural mineral resources. This results in high production costs and huge demand, consuming vast amounts of natural resources. Furthermore, ordinary silicate cement is calcined at very high temperatures, generally above 1450–1500℃, consuming enormous amounts of fuel and generating substantial carbon emissions.

[0003] Currently, the discharge and storage of industrial solid waste such as tailings and steel slag not only occupy a large amount of land resources but also cause direct and irreversible harm to the soil environment. The main components of lead-zinc tailings and steel slag are oxides of calcium, silicon, aluminum, and iron, which also contain harmful elements such as heavy metals. Heavy metals like zinc, lead, cadmium, and manganese pose a leaching risk, significantly reducing their utilization rate in building materials. Existing ordinary silicate cement has high calcination energy consumption, necessitating an improvement in the comprehensive utilization rate of solid waste resources from the aluminosilicate industry. Many existing solid waste utilization methods, due to limitations in the performance requirements of the target products, are difficult to scale up from the laboratory and pilot-scale testing stages to industrialization, resulting in high technical costs. Summary of the Invention

[0004] Purpose of the invention: In order to overcome the shortcomings of the existing technology, the purpose of this invention is to provide a low-calcination-temperature, green and low-carbon cement clinker based on composite tailings and steel slag. Another purpose of this invention is to provide a low-cost method for preparing cement clinker based on composite tailings and steel slag.

[0005] Technical Solution: The present invention discloses a cement clinker based on composite tailings and steel slag, comprising the following raw materials in parts by weight: limestone 68.0–75.0 parts, lead-zinc tailings 10.5–20.7 parts, granite tailings 5.1–6.1 parts, and steel slag 5.2–12.5 parts; the cement clinker contains more than 20 wt% tetracalcium aluminoferrite and less than 50 wt% tricalcium silicate. It has a low tricalcium silicate content, while having higher contents of dicalcium silicate and tetracalcium aluminoferrite.

[0006] Furthermore, limestone accounts for 68–73 wt% of the total mass of limestone, lead-zinc tailings, granite tailings, and steel slag. Lead-zinc tailings, granite tailings, and steel slag account for 27–29 wt% of the total mass of raw materials. This significantly increases the proportion of industrial solid waste in cement production raw materials, expands the applicability of solid waste resources in the building materials field, and conserves natural resources.

[0007] The above-mentioned method for preparing cement clinker based on composite tailings and steel slag includes the following steps:

[0008] Step 1: Weigh the raw materials according to the weight ratio, ball mill, dry, and sieve;

[0009] Step 2: Place the material obtained in Step 1 into a tableting mold and press it into a round tablet;

[0010] Step 3: The circular plates are heated in a stepped manner to 1350-1375℃ and held at that temperature to obtain fired cement clinker;

[0011] Step 4: Rapidly cool the fired cement clinker to below 300°C;

[0012] Step 5: Grind the material obtained in Step 4 to below 200 mesh using a vibratory mill to obtain cement clinker based on composite tailings and steel slag.

[0013] Further, in step one, the ball mill speed is 300–350 r / min, the time is 30–60 min, and the material-to-ball ratio is 1:2–3. The drying temperature is 60–80℃, and the drying time is 6–8 h. Sieving is performed through a 200–325 mesh sieve. A ball mill speed less than 300 r / min will result in insufficient grinding fineness of the cement raw meal and uneven mixing; a ball mill speed greater than 350 r / min will cause the raw meal to settle and clump at the bottom of the ball mill jar. A drying temperature below 60℃ will result in too low a moisture evaporation efficiency; a drying temperature above 80℃ will result in unnecessary energy consumption.

[0014] Furthermore, in step two, the thickness of the disc is 5–7 mm.

[0015] Furthermore, in step three, the stepped heating regime is as follows: heat to 900–1000℃ at a rate of 8–10℃ / min, then heat to 1350–1375℃ at a rate of 4–5℃ / min, and hold for 45–60 minutes. Insufficient holding time may result in incomplete high-temperature remodeling reaction of cement raw materials, leading to poor cement stability; excessive holding time may cause overburning, adversely affecting the activity of clinker mineral phases and reducing the quality of cement clinker. A heating rate greater than 10℃ / min in the first stage or greater than 5℃ / min in the second stage may cause malfunctions in the laboratory's high-temperature heating equipment.

[0016] Furthermore, in step four, rapid cooling is carried out by an industrial fan with a wind speed of 2-3 m / s and a cooling time of 10-15 min, to prevent the decomposition of the C3S mineral phase and the unfavorable transformation of the C2S mineral phase crystal form.

[0017] Furthermore, in step five, the vibration frequency of the vibratory mill is 1000-1200 r / min, the amplitude is 10-15 min, and the vibration time is 5-10 min, so as to quickly and efficiently crush and grind the relatively hard cement clinker after firing into powder.

[0018] Preparation Principle: The main components of industrial aluminosilicate solid wastes such as lead-zinc tailings, granite tailings, and steel slag are similar to those of cement raw materials. They can partially or completely replace the SiO2, Fe2O3, Al2O3, and CaO required for cement clinker production, saving raw materials and fuel for cement clinker production, disposing of industrial solid waste, and reducing production costs and carbon emissions. Due to the different effects of various components on clinker calcination during the high-temperature reconstruction reaction, their synergistic effect promotes interionic reactions, contributing to the achievement of low eutectic characteristics. The Fe2O3 component in lead-zinc tailings and steel slag can serve as the iron source for tetracalcium aluminoferrite in the clinker, increasing the liquid phase content and viscosity during calcination, and promoting the formation and crystallization of the silicate phase in cement. The alkali metal oxides and other trace elements in lead-zinc tailings and steel slag can act as mineralizing agents to effectively reduce the cement calcination temperature, significantly reducing the energy consumption of cement clinker calcination and resulting in high economic benefits. Meanwhile, during the hydration process of high-speed rail low-calcium phase cement clinker, the hydration products of high-content tetracalcium aluminoferrite have a dense structure, which plays a good role in chemical solidification and physical sealing of heavy metal elements in lead-zinc tailings and steel slag, effectively reducing the risk of heavy metal leaching.

[0019] Beneficial effects: Compared with the prior art, the present invention has the following significant features:

[0020] 1. It helps reduce the accumulation of tailings and steel slag resources, effectively improves the comprehensive utilization rate of solid waste resources in the aluminosilicate industry and the scope of its use in the building materials field. It has a strong ability to solidify heavy metal elements and is suitable for application in building materials to realize industrialization.

[0021] 2. Using lead-zinc tailings and steel slag to replace cement raw materials in the production of cement clinker not only reduces the production cost of cement clinker, but also utilizes the low eutectic properties of heavy metals and other harmful elements in solid waste at high temperatures to reduce the temperature and time of the appearance of the molten liquid phase during the calcination process of cement clinker, significantly reducing the calcination temperature and reducing energy consumption in the production process.

[0022] 3. The high-iron low-calcium phase cement clinker prepared by this invention has a tetracalcium aluminoferrite content of over 20% and a tricalcium silicate content of less than 50%. It belongs to medium-heat silicate cement clinker, with low hydration exothermic heat and high early strength. It effectively solidifies harmful metal elements in solid waste, reduces the risk of heavy metal leaching during solid waste storage, reduces potential harm to the ecological environment and human health, and realizes the harmless utilization of solid waste resources in aluminosilicate industry. Attached Figure Description

[0023] Figure 1 This is the XRD pattern of the present invention. Detailed Implementation

[0024] In the following embodiments, limestone provided by Guangxi Yufeng Cement Plant and lead-zinc tailings provided by Jilin Zijian New Materials Co., Ltd. were used. The raw materials consisted of limestone (CaO content of about 65wt%), granite tailings (SiO2 content of about 80wt%), steel slag (CaO content of about 45wt%, Fe2O3 content of about 25wt%), and lead-zinc tailings (SiO2 content of about 40wt%, Fe2O3 content of about 25wt%).

[0025] Example 1

[0026] A method for preparing high-iron, low-calcium phase cement clinker based on composite tailings and steel slag includes the following steps:

[0027] (1) Weigh 71.5 parts of raw material limestone, 10.5 parts of lead-zinc tailings, 5.5 parts of granite tailings, and 12.5 parts of steel slag. The total mass of lead-zinc tailings, granite tailings, and steel slag accounts for 28.5 wt% of the total mass of raw materials. Ball mill at 300 r / min for 40 min. The ball milling media is zirconia balls, and the material-to-ball ratio is 1:2. Dry at 60℃ for 6 h and pass through a 200 mesh sieve.

[0028] (2) Take an appropriate amount of the material obtained in step (1) and put it into the tableting mold to press it into a round sheet. The diameter of the round sheet is 30mm and the thickness is 5mm.

[0029] (3) Place the round pieces obtained in step (2) into a blast furnace box furnace, heat them to 1000℃ at 10℃ / min, heat them to 1350℃ at 5℃ / min, and hold them for 60 min to obtain high-temperature calcined cement clinker.

[0030] (4) Quickly transfer the calcined high-temperature clinker to an industrial electric fan and rapidly cool it for 15 minutes at a wind speed of 3 m / s.

[0031] (5) The cooled clinker obtained in step (4) is placed in a vibrating mill with a vibration frequency of 1000 r / min, an amplitude of 10 min, and a vibration time of 10 min. It is then passed through a 200-mesh sieve to obtain high-iron low-calcium phase cement clinker based on composite tailings and steel slag.

[0032] (6) The clinker powder sample obtained in step (5) was subjected to XRD test, and based on the structural model and the XRDRietveld refinement principle, the nonlinear least squares method was used to perform full spectrum fitting on the data spectrum to obtain the contents of tetracalcium aluminoferrite (C4AF) and tricalcium silicate (C3S) in the clinker sample, as shown in Table 1 below.

[0033] Example 2

[0034] A method for preparing high-iron, low-calcium phase cement clinker based on composite tailings and steel slag includes the following steps:

[0035] (1) Weigh 68 parts of raw material limestone, 20.7 parts of lead-zinc tailings, 6.1 parts of granite tailings, and 5.2 parts of steel slag. The total mass of lead-zinc tailings, granite tailings, and steel slag accounts for 32 wt% of the total mass of raw materials. Ball mill at 350 r / min for 40 min. The ball milling media is zirconia balls, and the material-to-ball ratio is 1:2. Dry at 60℃ for 6 h and pass through a 200 mesh sieve.

[0036] (2) Take an appropriate amount of the material obtained in step (1) and put it into the tableting mold to press it into a round sheet. The diameter of the round sheet is 30mm and the thickness is 5mm.

[0037] (3) Place the round pieces obtained in step (2) into a blast furnace box furnace, heat them to 1000℃ at 10℃ / min, heat them to 1350℃ at 5℃ / min, and hold them for 60 min to obtain high-temperature calcined cement clinker.

[0038] (4) Quickly transfer the calcined high-temperature clinker to an industrial electric fan and rapidly cool it for 15 minutes at a wind speed of 3 m / s.

[0039] (5) The cooled clinker obtained in step (4) is placed in a vibrating mill with a vibration frequency of 1000 r / min, an amplitude of 10 min, and a vibration time of 10 min. It is then passed through a 200-mesh sieve to obtain high-iron low-calcium phase cement clinker based on composite tailings and steel slag.

[0040] Example 3

[0041] A method for preparing high-iron, low-calcium phase cement clinker based on composite tailings and steel slag includes the following steps:

[0042] (1) Weigh 75 parts of raw material limestone, 14.3 parts of lead-zinc tailings, 5.1 parts of granite tailings, and 5.6 parts of steel slag. The total mass of lead-zinc tailings, granite tailings, and steel slag accounts for 25 wt% of the total mass of raw materials. Ball mill at 300 r / min for 40 min. The ball milling media is zirconia balls, and the material-to-ball ratio is 1:2. Dry at 60℃ for 6 h and pass through a 200 mesh sieve.

[0043] (2) Take an appropriate amount of the material obtained in step (1) and put it into the tableting mold to press it into a round sheet. The diameter of the round sheet is 30mm and the thickness is 5mm.

[0044] (3) Place the round pieces obtained in step (2) into a blast furnace box furnace, heat them to 1000℃ at 10℃ / min, heat them to 1350℃ at 5℃ / min, and hold them for 60 min to obtain high-temperature calcined cement clinker.

[0045] (4) Quickly transfer the calcined high-temperature clinker to an industrial electric fan and rapidly cool it for 15 minutes at a wind speed of 3 m / s.

[0046] (5) The cooled clinker obtained in step (4) is placed in a vibrating mill with a vibration frequency of 1000 r / min, an amplitude of 10 min, and a vibration time of 10 min. It is then passed through a 200-mesh sieve to obtain high-iron low-calcium phase cement clinker based on composite tailings and steel slag.

[0047] Table 1. 28-day hydration strength and main mineral phase content of high-speed ferrous low-calcium phase cement clinker

[0048] Strength (MPa) 67.31 76.87 69.04 <![CDATA[C3S(wt.%)]]> 45.47 49.92 47.89 <![CDATA[C4AF(wt.%)]]> 24.75 18.87 19.56

[0049] Table 2. Leaching concentrations and limits (mg / L) of heavy metals

[0050] Zn <0.02 <0.02 <0.02 1.0 Cd <0.02 <0.02 <0.02 0.03 Pb <0.02 <0.02 <0.02 0.3 Mn <0.02 <0.02 <0.02 1.0 Cr <0.02 <0.02 <0.02 0.2

[0051] X-ray diffraction analysis was performed on the high-iron, low-calcium phase cement clinker prepared in Examples 1-3. The XRD diffraction patterns are shown below. Figure 1 As shown, the C4AF content in the sample of Example 1 was significantly higher than that in Examples 2 and 3, with an increase of up to 18.51%. The reason for this is that steel slag is rich in Fe2O3, and compared to traditional iron-based cement raw materials, it has a higher iron content. More Fe2O3 participates in the reaction during the cement raw material process, leading to the formation of more C4AF. In Examples 2 and 3, the actual proportion of clinker mineral phases did not differ much, all being less than 10%. It can be seen that, with a fixed amount of steel slag, changes in the amount of lead-zinc tailings have a relatively small impact on the mineral phase content, and the C3S content of the clinker is relatively high. This implies that the mix design of the combined solid waste group is reasonable, and the trace elements abundant in the solid waste are related to the reduction of the initial temperature for the formation of the molten liquid phase.

[0052] The hydration strength test results of the high-iron, low-calcium phase cement clinker prepared in Examples 1-3 after 28 days are shown in Table 1 above. The sample in Example 2 had the highest strength value, which was 14.20% and 11.34% higher than that of the samples in Examples 1 and 3, respectively. High amounts of lead-zinc tailings significantly promoted the hydration strength. This is because sulfur (S) solidified in the clinker can react with Ca(OH)₂ to generate CaSO₄, which has a high heat of hydration, thus accelerating the cement hydration reaction. Furthermore, sulfur in the raw meal may also improve the grindability of the cement clinker and reduce the particle size of cement particles, thereby increasing the cement hydration strength.

[0053] The leaching results of heavy metal elements in hardened cement paste are shown in Table 2 above. The results show that under neutral conditions, heavy metal ions such as Zn, Cd, Pb, Mn, and Cr did not leach out, and the leaching concentrations were all below the instrument detection limits, far below the standard leaching concentration limits. This is because after high-temperature calcination, heavy metal elements such as Cu, Mn, Zn, Cd, As, and Pb in the raw material are stably present in the form of solid solutions and oxides, and can exist stably in a neutral environment with a pH of 7. The results indicate that high-iron, low-calcium phase cement clinker has a good solidification effect on heavy metal elements.

[0054] Example 4

[0055] A method for preparing high-iron, low-calcium phase cement clinker based on composite tailings and steel slag includes the following steps:

[0056] (1) Weigh 71.5 parts of raw material limestone, 10.5 parts of lead-zinc tailings, 5.5 parts of granite tailings, and 12.5 parts of steel slag. The total mass of lead-zinc tailings, granite tailings, and steel slag accounts for 28.5 wt% of the total mass of raw materials. Ball mill at 300 r / min for 40 min. The ball milling media is zirconia balls, and the material-to-ball ratio is 1:2. Dry at 60℃ for 6 h and pass through a 200 mesh sieve.

[0057] (2) Take an appropriate amount of the material obtained in step (1) and put it into the tableting mold to press it into a round sheet. The diameter of the round sheet is 30mm and the thickness is 5mm.

[0058] (3) Place the round piece obtained in step (2) into a blast furnace box furnace, heat it to 1000℃ at 10℃ / min, heat it to 1375℃ at 5℃ / min, and hold it for 45 minutes to obtain high-temperature calcined cement clinker.

[0059] (4) Quickly transfer the calcined high-temperature clinker to an industrial electric fan and rapidly cool it for 15 minutes at a wind speed of 3 m / s.

[0060] (5) The cooled clinker obtained in step (4) is placed in a vibrating mill with a vibration frequency of 1000 r / min, an amplitude of 10 min, and a vibration time of 10 min. It is then passed through a 200-mesh sieve to obtain high-iron low-calcium phase cement clinker based on composite tailings and steel slag.

[0061] Example 5

[0062] A method for preparing high-iron, low-calcium phase cement clinker based on composite tailings and steel slag includes the following steps:

[0063] (1) Weigh 71.5 parts of raw material limestone, 10.5 parts of lead-zinc tailings, 5.5 parts of granite tailings, and 12.5 parts of steel slag. The total mass of lead-zinc tailings, granite tailings, and steel slag accounts for 28.5 wt% of the total mass of raw materials. Ball mill at 300 r / min for 40 min. The ball milling media is zirconia balls, and the material-to-ball ratio is 1:2. Dry at 60℃ for 6 h and pass through a 200 mesh sieve.

[0064] (2) Take an appropriate amount of the material obtained in step (1) and put it into the tableting mold to press it into a round sheet. The diameter of the round sheet is 30mm and the thickness is 5mm.

[0065] (3) Place the round piece obtained in step (2) into a blast furnace box furnace, heat it to 1000℃ at 10℃ / min, heat it to 1325℃ at 5℃ / min, and hold it for 60min to obtain high-temperature calcined cement clinker.

[0066] (4) Quickly transfer the calcined high-temperature clinker to an industrial electric fan and rapidly cool it for 15 minutes at a wind speed of 3 m / s.

[0067] (5) The cooled clinker obtained in step (4) is placed in a vibrating mill with a vibration frequency of 1000 r / min, an amplitude of 10 min, and a vibration time of 10 min. It is then passed through a 200-mesh sieve to obtain high-iron low-calcium phase cement clinker based on composite tailings and steel slag.

[0068] Comparative Example 1

[0069] The remaining steps of this comparative example are the same as those of Example 1, except that the highest temperature in step (3) is raised to 1375℃ and held for 45 minutes. The 28-day compressive strength was measured to be 68.43 MPa, indicating that the holding time can be reduced by increasing the calcination temperature in this invention, while ensuring the performance of the cement clinker.

[0070] Comparative Example 2

[0071] The remaining steps of this comparative example are the same as those in Example 1, except that the highest temperature in step (3) is lowered to 1325℃. The 28-day compressive strength was measured to be 49.26 MPa, and the free calcium oxide content exceeded 1.5%, which does not meet national standards. This indicates that the minimum calcination temperature in this invention is 1350℃. Temperatures below this will reduce the hydration performance of cement clinker and cause poor stability of the cement clinker.

[0072] Of the above embodiments, the optimal embodiment is Embodiment 1, which has the highest iron phase content and a tetracalcium aluminoferrite mass percentage exceeding 24 wt%, ensuring low eutectic properties among the oxide components during calcination, reducing the calcination temperature, and resulting in lower heat release and rate during hydration. The resulting cement stone exhibits good wear resistance and strong resistance to chloride ions and sulfates, making it suitable for large-volume and marine concrete applications. Furthermore, the lowest calcination temperature among all embodiments reduces costs and carbon emissions.

Claims

1. A method for preparing cement clinker based on composite tailings and steel slag, characterized in that, Includes the following steps: Step 1: Weigh the raw materials according to the weight ratio, ball mill, dry, and sieve; Step 2: Place the material obtained in Step 1 into a tableting mold and press it into a round tablet; Step 3: The circular plates are heated in a stepped manner to 1350~1375℃ and held at that temperature to obtain fired cement clinker; Step 4: Rapidly cool the fired cement clinker to below 300°C; Step 5: Grind the material obtained in Step 4 to below 200 mesh using a vibratory mill to obtain cement clinker based on composite tailings and steel slag; In step three, the stepped heating regime is as follows: the temperature is increased to 900-1000℃ at 8-10℃ / min, then increased to 1350-1375℃ at 4-5℃ / min, and held for 45-60min. In step four, rapid cooling is performed by an industrial fan with a wind speed of 2-3 m / s and a cooling time of 10-15 min. The cement clinker based on composite tailings and steel slag comprises the following raw materials in parts by weight: limestone 68.0~75.0 parts, lead-zinc tailings 10.5~20.7 parts, granite tailings 5.1~6.1 parts, and steel slag 5.2~12.5 parts; the mass percentage of tetracalcium aluminoferrite in the cement clinker exceeds 20 wt%, and the mass percentage of tricalcium silicate is less than 50 wt%.

2. The method for preparing cement clinker based on composite tailings and steel slag according to claim 1, characterized in that: The total mass of limestone accounts for 68-73 wt% of the total mass of limestone, lead-zinc tailings, granite tailings, and steel slag.

3. The method for preparing cement clinker based on composite tailings and steel slag according to claim 1, characterized in that: In step one, the ball mill rotation speed is 300~350 r / min, the time is 30~60 min, and the material-to-ball ratio is 1:2~3.

4. The method for preparing cement clinker based on composite tailings and steel slag according to claim 1, characterized in that: In step one, the drying temperature is 60~80℃ and the drying time is 6~8h.

5. The method for preparing cement clinker based on composite tailings and steel slag according to claim 1, characterized in that: In step one, the sieving is performed through a 200-325 mesh sieve.

6. The method for preparing cement clinker based on composite tailings and steel slag according to claim 1, characterized in that: In step two, the thickness of the disc is 5-7 mm.

7. The method for preparing cement clinker based on composite tailings and steel slag according to claim 1, characterized in that: In step five, the vibration frequency of the vibratory mill is 1000~1200 r / min, the amplitude is 10~15 min, and the vibration time is 5~10 min.

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