A method for co-disposing phosphogypsum by using inferior coal and preparing low-carbon clinker

Abstract

The present invention discloses a method for co-processing phosphogypsum and preparing low-carbon clinker by utilizing inferior coal, comprising the following steps: (1) obtaining phosphogypsum, inferior coal, and silicon-aluminum-iron raw materials, drying and crushing them, and then mixing and grinding them according to the designed C:S, KH value, and total CaO:SiO2 mass ratio; (2) adding water to the obtained mixture to form pellets, and drying them; (3) calcining the dried pellets in an oxygen-deficient rotary kiln, and cooling them to obtain low-carbon clinker. The present invention proposes for the first time to use inferior coal of low quality and difficulty in application to replace traditional reducing carbonaceous materials, using phosphogypsum, inferior coal, and silicon-aluminum-iron raw materials as the main raw materials, and adopting a one-step calcination method to achieve efficient preparation of low-carbon clinker; the obtained low-carbon clinker has an SO3 content of ≤1% and a C3S2 content of ≥50%; and the requirements for production equipment and conditions are not high, with significant economic and environmental benefits, making it suitable for promotion and application.

Description

Technical Field

[0001] The present invention belongs to the technical field of building materials, and in particular relates to a method for co-processing phosphogypsum and preparing low-carbon clinker by utilizing inferior coal. Background Art

[0002] Phosphogypsum is a solid waste generated during the wet-process phosphoric acid production process. Its composition is complex, consisting of hydrated calcium sulfate, incompletely decomposed phosphate rock, residual phosphoric acid, fluoride, acid-insoluble matter, and organic matter. The presence of fluorine and organic matter has the greatest impact on the resource utilization of phosphogypsum. Stockpiling occupies significant land and pollutes water and land resources. The resource utilization and safe and efficient use of phosphogypsum are crucial for addressing the environmental pollution and resource waste associated with its stockpiling.

[0003] Using phosphogypsum as a CaO source in cement clinker production, replacing limestone, is a challenging and significant approach to addressing the resource utilization of phosphogypsum. However, compared to CaCO3, CaSO4 requires higher temperatures to fully decompose and desulfurize, increasing operational complexity and cost. Even after high-temperature calcination, it can still be found in large quantities, which undoubtedly restricts the effective application of phosphogypsum. Decomposing CaSO4 at low temperatures requires the use of carbonaceous raw materials as reducing agents. Conventional carbonaceous raw materials, such as coke and pulverized coal, are expensive, increasing the cost of processing phosphogypsum.

[0004] During coal mining, a large amount of low-quality coal is often encountered. Low-quality coal has high ash and sulfur content, low fixed carbon content, and low calorific value. The main reasons why low-quality coal is difficult to use are: (1) it pollutes the atmosphere when burned, forming smog, which is harmful to human health; (2) it has low calorific value and short combustion time; (3) it has high ash content, making it difficult to fully burn, which seriously affects the clinker quality of the cement industry. How to achieve the coordinated disposal of low-quality coal and phosphogypsum, reduce the coal cost when disposing of phosphogypsum, and produce environmentally friendly materials has become a technical problem that needs to be solved urgently. Summary of the Invention

[0005] The main purpose of the present invention is to provide a method for co-processing phosphogypsum and preparing low-carbon clinker using inferior coal, which can effectively reduce the coal cost when processing phosphogypsum and produce environmentally friendly low-carbon clinker. The preparation method involved is relatively simple, has low requirements on production equipment and conditions, and is suitable for promotion and application.

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

[0007] A method for co-processing phosphogypsum and preparing low-carbon clinker using low-quality coal comprises the following steps:

[0008] (1) Obtaining phosphogypsum, inferior coal, and silicon-aluminum-iron raw materials, drying and crushing them, batching them according to the designed C:S, KH value, and total CaO:SiO2 mass ratio, and mixing and grinding them;

[0009] (2) adding water to the obtained mixture to form pellets and drying;

[0010] (3) The dried pellets are calcined in an oxygen-deficient rotary kiln and cooled to obtain low-carbon clinker.

[0011] According to the above scheme, the low-quality coal in step (1) has a fixed carbon content of ≤45%, an ash content of ≥40%, a sulfur content of ≥3% (preferably a sulfur content of ≥3.5%), and a calorific value of less than 4000 kcal. Conventional ordinary coal, high-sulfur coal, and coke have a fixed carbon content of >45%, a calorific value of more than 4000 kcal, an ash content of ≤25%, a sulfur content of ≤1% for ordinary coal and coke, and a sulfur content of ≥3% for high-sulfur coal, but lower than that of low-quality coal.

[0012] According to the above scheme, the silicon-aluminum-iron raw material in step (1) is one or more of sandstone, coal gangue, silica, clay, fly ash, and various types of waste residues.

[0013] According to the above scheme, the design value of C:S in step (1) is 0.7-0.9, the design value of KH value is 0.38-0.48, and the total CaO:SiO2 mass ratio in the chemical composition is 1.35-1.60.

[0014] Furthermore, the ingredients are adjusted to have an SM value of 3-6.

[0015] According to the above scheme, the diameter of the ball in step (2) is 1-3 cm.

[0016] According to the above scheme, the calcination temperature in step (3) is 1150-1250°C, the calcination time is 5-30 minutes, and the O2 concentration in the calcination environment is 0-10 vol%.

[0017] Furthermore, the O2 concentration of the calcining environment is 5-10 vol%, which has a relatively low requirement on the oxygen content of the calcining environment and is suitable for industrial promotion and application.

[0018] According to the above scheme, the SO3 content of the low-carbon clinker obtained in step (3) is ≤1% and the C3S2 content is ≥50%.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] 1) The present invention proposes for the first time to use low-quality and difficult-to-use inferior coal to replace traditional reducing carbonaceous materials, which can significantly reduce the coal cost when disposing of large amounts of phosphogypsum; at the same time, it can turn inferior coal into superior coal, utilizing the negative sulfur content and the property that it is not easy to fully burn, to achieve a better effect on the reduction and decomposition of phosphogypsum; the SO2 generated by the inferior coal and the SO2 generated by the decomposition of phosphogypsum are jointly fed into the subsequent two-transfer and two-absorption device for acid production.

[0021] 2) The present invention uses phosphogypsum, inferior coal, and silicon-aluminum-iron raw materials as main raw materials, and adopts a one-step calcination method to achieve efficient preparation of low-carbon clinker. Compared with traditional desulfurization furnaces and other equipment, the rotary kiln used has a larger gas volume share and faster circulation, and the O2 content is difficult to control at a low value. The inferior coal used in the present invention has a low fixed carbon content and a high ash content, and is not easy to fully burn, which is conducive to promoting more fixed carbon to directly participate in the decomposition and desulfurization reaction of phosphogypsum in the form of C. At the same time, combined with the design value of C:S, KH value, SM value, total CaO:SiO2 mass ratio and other control measures, efficient resource utilization of inferior coal and phosphogypsum in the field of low-carbon clinker preparation is achieved.

[0022] 3) Under the premise of using low-quality coal, the present invention can achieve a high desulfurization rate of phosphogypsum by performing a one-step calcination, and produce low-carbon clinker with an SO3 content of ≤1% and a C3S2 content of ≥50%, which has significant economic and environmental benefits; and has low requirements on production equipment and conditions, and is suitable for promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The XRD pattern of the calcined product obtained in Example 1 is shown in FIG. DETAILED DESCRIPTION

[0024] The technical solution of the present invention is further described below through specific implementation methods. In order to better illustrate the present invention and facilitate understanding of the technical solution of the present invention, typical but non-limiting embodiments of the present invention are as follows.

[0025] In the following examples, the chemical composition analysis results of a batch of phosphogypsum, coal gangue, fly ash, iron ore soil, and silica are shown in Table 1:

[0026] Table 1 Chemical composition analysis (wt%)

[0027] name Loss on ignition <![CDATA[SiO2]]> <![CDATA[Al2O3]]> <![CDATA[Fe2O3]]> CaO MgO <![CDATA[SO3]]> <![CDATA[K2O]]> <![CDATA[Na2O]]> Phosphogypsum 19.27 6.6 0.23 0.52 29.66 0.03 42.46 0.37 0.08 coal gangue 4.63 76.3 6.62 4.64 1.91 2.35 0.48 1.34 0.55 fly ash 5.33 43.41 32.88 6.44 6.72 0.7 1.2 0.81 0.47 Iron ore soil 3.27 48.9 15.55 15.9 7.56 4.41 0.01 0.78 2.79 silica 1.65 94.56 1.25 1.12 0.35 0.17 0.15 0.31 0.14

[0028] The low-quality coal used was subjected to conventional analysis and chemical composition analysis of the ash, and the results are shown in Table 2 and Table 3 respectively:

[0029] Table 2 Conventional analysis of low-quality coal (wt%)

[0030] name Moisture ash content Volatile matter Fixed carbon content Total sulfur Qnet,ad Qnet,d Low-quality coal 3.14 48.68 8.26 39.92 3.87 13.18 14.08

[0031] Table 3 Chemical composition analysis of ash of low-quality coal (wt%)

[0032]

[0033] Example 1

[0034] A method for co-processing phosphogypsum and preparing low-carbon clinker using low-quality coal comprises the following steps:

[0035] 1. Ratio design

[0036] The SO3 in the chemical composition of phosphogypsum is included in its own ignition loss, and the remaining chemical composition is measured according to the ignition loss 19.27% + 42.46% = 61.73%. The remaining chemical composition corresponds to the substance mainly composed of CaO, and the design ratio with the silicon-aluminum-iron raw materials and inferior coal is based on the molar ratio of C in inferior coal to SO3 in phosphogypsum of 0.8146, KH value of 0.409, SM value of 4.150, and the mass ratio of total CaO to SiO2 in the chemical composition of 1.444. That is, the amount of inferior coal = amount of phosphogypsum * 0.4246 * 0.8146 * 12 /

[0037] (80*0.3992), the weight ratio of phosphogypsum: coal gangue: inferior coal is 87.2:12.8:11.34, and the weight of ash introduced by inferior coal is 11.34*0.4868=5.52. The ratio and corresponding indicators are shown in Table 4 and Table 5 respectively:

[0038] Table 4 Proportions

[0039]

[0040] Table 5 Indicators corresponding to the ratio

[0041] C:S KH SM IM <![CDATA[Total CaO:SiO2]]> 0.8146 0.409 4.150 2.022 1.444

[0042] 2. Ball making

[0043] The phosphogypsum, coal gangue and low-quality coal measured in the above ratio are mixed and ground, and then water is added to form balls with an average diameter of 2 cm, and then naturally dried for 1 day.

[0044] 3. Calcination

[0045] The naturally dried pellets are placed in an oxygen-deficient rotary kiln after burning coal (coal that provides temperature and heat) for calcination. The O2 concentration is 6%. After calcination, they are cooled to obtain low-carbon clinker. The calcination temperature of the kiln is set to 1200℃ and the time is 10 minutes.

[0046] Example 2

[0047] A method for co-processing phosphogypsum and preparing low-carbon clinker using low-quality coal comprises the following steps:

[0048] 1. Ratio design

[0049] The SO3 in the chemical composition of phosphogypsum is included in its own ignition loss, and the remaining chemical composition is measured according to the ignition loss 19.27% + 42.46% = 61.73%. The remaining chemical composition corresponds to the substance mainly composed of CaO, and the design ratio with the silicon-aluminum-iron raw materials and inferior coal is based on the molar ratio of C in inferior coal to SO3 in phosphogypsum of 0.8146, KH value of 0.416, SM value of 3.497, and the mass ratio of total CaO to SiO2 in the chemical composition of 1.507. That is, the amount of inferior coal = amount of phosphogypsum * 0.4246 * 0.8146 * 12 /

[0050] (80*0.3992), the weight ratio of phosphogypsum: iron ore soil: coal gangue: inferior coal is 87:3:10:11.31, and the weight of ash introduced by inferior coal is 11.31*0.4868=5.51. The ratio and corresponding indicators are shown in Table 6 and Table 7 respectively:

[0051] Table 6 Proportions

[0052]

[0053] Table 7 Indicators corresponding to the ratio

[0054] C:S KH SM IM <![CDATA[Total CaO:SiO2]]> 0.8146 0.416 3.497 1.787 1.507

[0055] 2. Ball making

[0056] The phosphogypsum, coal gangue and low-quality coal measured in the above ratio are mixed and ground, and then water is added to form balls with an average diameter of 2 cm, and then naturally dried for 1 day.

[0057] 3. Calcination

[0058] The naturally dried pellets are placed in an oxygen-deficient rotary kiln after burning coal (coal that provides temperature and heat) for calcination. The O2 concentration is 8%. After calcination, they are cooled to obtain low-carbon clinker. The calcination temperature of the kiln is set to 1200℃ and the time is 8 minutes.

[0059] Example 3

[0060] A method for co-processing phosphogypsum and preparing low-carbon clinker using low-quality coal comprises the following steps:

[0061] The SO3 in the chemical composition of phosphogypsum is included in its own ignition loss, and the remaining chemical composition is measured according to the loss on ignition 19.27% + 42.46% = 61.73%. The remaining chemical composition corresponds to the substance mainly composed of CaO. The proportioning is designed with the ferro-silica raw material and inferior coal according to the molar ratio of C in inferior coal to SO3 in phosphogypsum of 0.8146, KH value of 0.450, SM value of 5.517, and the mass ratio of total CaO to SiO2 in the chemical composition of 1.491. That is, the amount of inferior coal = the amount of phosphogypsum * 0.4246 * 0.8146 * 12 / (80 * 0.3992), the weight ratio of phosphogypsum: silica: inferior coal is 90.11:9.89:11.71, and the weight of ash introduced by the inferior coal is 11.71 * 0.4868 = 5.70. The proportioning and corresponding indicators are shown in Tables 8 and 9 respectively:

[0062] Table 8 Proportions

[0063]

[0064] Table 9 Indicators corresponding to the ratio

[0065] C:S KH SM IM <![CDATA[Total CaO:SiO2]]> 0.8146 0.450 5.517 2.288 1.491

[0066] The other steps are the same as those in Example 2.

[0067] Comparative Example 1

[0068] A method for preparing low-carbon clinker using phosphogypsum, wherein the preparation steps are substantially the same as those in Example 2, except that ordinary pulverized coal is used instead of inferior coal. The results of conventional analysis of the pulverized coal and chemical composition analysis of the ash are shown in Tables 10 and 11, respectively:

[0069] Table 10 Conventional analysis of coal powder

[0070] name Moisture ash content Volatile matter Fixed carbon content Total sulfur Qnet,ad Qnet,d Pulverized coal 3.23 15.14 32.30 49.33 0.97 25.51 27.43

[0071] Table 11 Chemical composition analysis of ash in coal powder

[0072]

[0073] The SO3 in the chemical composition of phosphogypsum is calculated into its own ignition loss, and the ignition loss is 19.27% + 42.46% = 61.73%. The remaining chemical composition corresponds to the substance mainly composed of CaO, and the molar ratio of C in the coal powder to SO3 in the phosphogypsum is 0.8146 (so that the fixed carbon content provided by the coal powder in the ratio is equal to that of the inferior coal in Example 2), the KH value is 0.415, the SM value is 3.499, and the total CaO in the chemical composition is 0.8146. The designed proportion is 1.506 for the mass ratio of coal powder to SiO2, that is, the amount of coal powder = the amount of phosphogypsum * 0.4246 * 0.8146 * 12 / (80 * 0.4933), the weight ratio of phosphogypsum: fly ash: iron ore soil: coal gangue: coal powder is 82.9:4.4:2.8:9.9:8.79, and the weight of ash introduced by coal powder is 8.79 * 0.1514 = 1.33. The final proportion is similar to that of Example 2. The proportions and corresponding indicators are shown in Table 12 and Table 13 respectively:

[0074] Table 12 Proportions

[0075]

[0076]

[0077] Table 13 Indicators corresponding to the ratio

[0078] C:S KH SM IM <![CDATA[Total CaO:SiO2]]> 0.8146 0.415 3.499 1.780 1.506

[0079] Comparative Example 2

[0080] A method for preparing low-carbon clinker using phosphogypsum, wherein the preparation steps are substantially different from those in Example 2, except that high-sulfur coal is used instead of low-quality coal. The results of conventional analysis of the high-sulfur coal and chemical composition analysis of the ash are shown in Tables 14 and 15, respectively:

[0081] Table 14 Conventional analysis of high sulfur coal

[0082] name Moisture ash content Volatile matter Fixed carbon content Total sulfur Qnet,ad Qnet,d High sulfur coal 1.42 23.48 10.25 64.85 2.99 25.25 26.33

[0083] Table 15 Chemical composition analysis of ash of high sulfur coal

[0084]

[0085] The SO3 in the chemical composition of phosphogypsum is calculated into its own ignition loss, and the remaining chemical composition is measured according to the ignition loss 19.27% + 42.46% = 61.73%, and the remaining chemical composition corresponds to the substance mainly composed of CaO, and the molar ratio of C in high-sulfur coal to SO3 in phosphogypsum is 0.8146 (so that the fixed carbon content provided by the high-sulfur coal in the ratio is equal to that of the inferior coal in Example 2), the KH value is 0.416, the SM value is 3.497, and the total CaO in the chemical composition is 0.8146. The mass ratio of SiO2 is 1.508, and the designed ratio is that the amount of high-sulfur coal is = the amount of phosphogypsum * 0.4246 * 0.8146 * 12 / (80 * 0.6485), the weight ratio of phosphogypsum: fly ash: iron ore soil: coal gangue: high-sulfur coal is 83.4:4.7:1.8:10.1:6.67, and the weight of ash introduced by high-sulfur coal is 6.67 * 0.2348 = 1.57. The final ratio is similar to that of Example 2. The ratio and corresponding indicators are shown in Table 16 and Table 17 respectively:

[0086] Table 16 Proportions

[0087]

[0088] Table 17 Indicators corresponding to the ratio

[0089] C:S KH SM IM <![CDATA[Total CaO:SiO2]]> 0.8146 0.416 3.497 1.789 1.508

[0090] Comparative Example 3

[0091] A method for preparing low-carbon clinker using phosphogypsum, wherein the preparation steps are substantially different from those of Example 2, except that: the high-sulfur coal in Comparative Example 2 is used, SO3 in the chemical composition of phosphogypsum is calculated into its own ignition loss, and the ignition loss is 19.27% + 42.46% = 61.73%, and the remaining chemical components are measured according to the substance mainly composed of CaO, and the molar ratio of C in the carbonaceous raw material to SO3 in the phosphogypsum is 0.8146, the KH value is 0.475, and the S is added. The M value is 6.629, and the mass ratio of total CaO to SiO2 in the chemical composition is 1.491. The designed proportion is that the amount of high-sulfur coal = the amount of phosphogypsum * 0.4246 * 0.8146 * 12 / (80 * 0.6485), the weight ratio of phosphogypsum: coal gangue 2: high-sulfur coal is 86:14:6.88, and the weight of ash introduced by high-sulfur coal is 6.88 * 0.2348 = 1.62. When using coal gangue 2 with a higher SiO2 content, the proportions and corresponding indicators are shown in Tables 18 and 19 respectively:

[0092] Table 18 Proportions

[0093]

[0094] Table 19 Indicators corresponding to the ratio

[0095] C:S KH SM IM <![CDATA[Total CaO:SiO2]]> 0.8146 0.475 6.629 1.115 1.491

[0096] In addition to using the temperature of 1200°C described in the present invention, each embodiment and comparative example further set a calcination temperature of 1100°C for comparison. The SO3 content of the calcined product (clinker) is shown in Table 20, and the SO3 content is measured by total sulfur analysis. The main mineral content is shown in Table 21, and the main mineral content is obtained by analyzing the XRD pattern of the calcined product (clinker) using jade software.

[0097] Table 20 SO3 content of calcined product (clinker)

[0098] project <![CDATA[SO3 content after firing at 1100℃]]> <![CDATA[SO3 content after firing at 1200℃]]> Example 1 2.88％ 0.76％ Example 2 3.24％ 0.92％ Example 3 3.29％ 0.69％ Comparative Example 1 3.40％ 1.35％ Comparative Example 2 3.31％ 1.27％ Comparative Example 3 3.42％ 1.08％

[0099] Table 21 Main mineral content (%)

[0100]

[0101]

[0102] Research shows that:

[0103] The present invention uses inferior coal to replace traditional reducing carbon materials. Due to its low fixed carbon content and high ash content, it is not easy to fully burn, which is conducive to creating a better reducing environment. At the same time, combined with the promoting effect of its negative sulfur, as well as the design value of C:S, KH value, SM value, total CaO:SiO2 mass ratio and other control measures, it can achieve efficient utilization of inferior coal and phosphogypsum in the field of low-carbon clinker preparation.

[0104] The XRD pattern of the calcined product obtained in Example 1 is as follows: Figure 1 As shown, combined Figure 1 It can be seen from Table 16 and Table 17 that a high desulfurization rate has been achieved at 1100℃, and no CaSO4 peak can be seen. Desulfurization is based on the formation of C2S. A large amount of C3S2 can be formed when the calcination temperature is increased to 1200℃. The calcination product at 1100℃ is mainly C2S, which can be used as a highly active mixed material and admixture; the calcination product at 1200℃ is clinker with C3S2≥50%, that is, low-carbon clinker.

[0105] It can be seen from Comparative Example 1 and Example 2 that, under the premise that the fixed carbon content provided by the coal powder is equal, the final design ratio is similar to that of Example 2. At this time, the SO3 content after desulfurization in Comparative Example 1 is higher than that in Example 2, and the SO3 content at 1200°C cannot be reduced to below 1%. In addition to fixed carbon, other substances that can play a reducing role are volatile matter and negative sulfur. The difference between the two types of coal is that the coal powder has a high volatile matter content and a low ash content, which is easy to burn fully, while the negative sulfur content and ash content introduced by the inferior coal are high and not easy to burn fully; Comparative Example 2 uses high-sulfur coal. Although the negative sulfur content is also high, it is lower than that of the inferior coal, and its ash content is low, which is easy to burn fully, and the SO3 content at 1200°C cannot be reduced to below 1%.

[0106] Example 3 and Comparative Example 3 respectively further increase the SM value to reduce the side effects of Al2O3 and Fe2O3 on desulfurization. Under the calcination atmosphere conditions of 8% O2 concentration described in the present invention, the SO3 content of the low-carbon clinker obtained under the calcination conditions of 1200°C in Example 3 using inferior coal is 0.69%, while the SO3 content of the low-carbon clinker obtained under the same calcination conditions in Comparative Example 3 using high-sulfur coal is 1.08%.

[0107] The above results show that, on the one hand, low-quality coal has a high sulfur content, and its negatively charged sulfur has a better effect on the reduction and decomposition of phosphogypsum. On the other hand, low-quality coal has a low fixed carbon content and a high ash content, which makes it difficult to fully burn, making it easier to create a reducing atmosphere. Moreover, more fixed carbon directly participates in the decomposition and desulfurization reaction of phosphogypsum in the form of C, making the use of low-quality coal more effective in rotary kilns with high O2 concentrations, and increasing the concentration of SO2 in the flue gas, which is beneficial for subsequent two-rotation and two-absorption acid production. The present invention can achieve the coordinated treatment of low-quality coal and phosphogypsum and the production of sulfuric acid, further reducing the coal cost when disposing of large amounts of phosphogypsum, and is more suitable for rotary kiln processes with low energy consumption and high output.

[0108] The above embodiments are only preferred embodiments of the present invention and cannot be used to limit the scope of protection of the present invention. Any non-substantial changes and replacements made by technicians in this field on the basis of the present invention fall within the scope of protection required by the present invention.

Claims

1. A method for co-processing phosphogypsum and preparing low-carbon clinker using low-quality coal, characterized in that: The following steps are involved: (1) obtaining phosphogypsum, inferior coal, and silicon-aluminum-iron raw materials, drying and crushing them, and then mixing and grinding them according to the designed C:S, KH value, and total CaO:SiO2 mass ratio; wherein the designed C:S value is 0.7-0.9, the designed KH value is 0.38-0.48, and the total CaO:SiO2 mass ratio in the chemical composition is 1.35-1.60; (2) Add water to the obtained mixture to form pellets and dry them; (3) The dried pellets are calcined in an oxygen-deficient rotary kiln and cooled to obtain low-carbon clinker; the calcination temperature is 1150-1250°C; The low-quality coal in step (1) has a fixed carbon content of ≤45%, an ash content of ≥40%, a sulfur content of ≥3%, and a calorific value of less than 4000 kcal; The hypoxic condition was an O2 concentration of 0-10 vol%.

2. The method according to claim 1, characterized in that The silicon-aluminum-iron raw material in step (1) is one or more of sandstone, coal gangue, silica, clay, fly ash and waste residue.

3. The method according to claim 1, characterized in that The diameter of the ball in step (2) is 1-3 cm.

4. The method according to claim 1, wherein The calcination time in step (3) is 5-30 minutes.

5. The low-carbon clinker prepared by the method according to any one of claims 1 to 4, characterized in that: Its SO3 content is ≤1% and its C3S2 content is ≥50%.

Images