Volume-stable high-magnesium Portland cement clinker, preparation method and high-magnesium Portland cement

Abstract

The invention discloses a volume-stable high-magnesium Portland cement clinker, a preparation method and high-magnesium Portland cement. The clinker is prepared from the following mineral components in percentage by weight: 45 to 60 percent of C3S, 15 to 25 percent of C2S, 5 to 10 percent of C3A, 10 to 15 percent of C4AF, 2 to 8 percent of Ca3Mg (SiO4) 2 and 0.1 to 1 percent of 3MgO. V2O5. By introducing the vanadium-containing waste catalyst, the sintering temperature of the clinker can be obviously reduced, a 3MgO. V2O5 compound is formed, free magnesium oxide is converted into a combined stable calcium-magnesium compound, the volume-stable high-magnesium Portland cement clinker is obtained, and the autoclaving expansion rate of the cement is less than 0.01% when the content of magnesium oxide in the clinker reaches 4.5-10%.

Description

Technical Field

[0001] The invention belongs to the technical field of Portland cement clinker building materials, and in particular relates to a volume-stable high-magnesium Portland cement clinker, a preparation method and high-magnesium Portland cement. Background Art

[0002] High-quality cement clinker is the basis for producing cement and concrete with excellent mechanical properties and good durability. With the development of the cement industry, high-quality high-calcium limestone resources are facing depletion, forcing a large number of enterprises to use high-magnesium low-grade limestone to produce cement clinker. The increase in magnesium content in clinker has caused a series of technical problems in process and materials, such as poor cement stability. Part of the magnesium oxide in cement clinker is dissolved in the clinker minerals, and the other part exists in a free state. The dissolved magnesium oxide has no expansion effect, while the free magnesium oxide forms periclase, which hydrates very slowly in water at room temperature. The free magnesium oxide hydrates to form magnesium hydroxide, and the volume expansion reaches 118%. When cement has been hardened for a long time, the expansion due to the hydration of periclase may damage mortar and concrete components, which is potentially harmful. Therefore, the national standard stipulates that the maximum content limit of magnesium oxide in clinker is below 5%, which makes cement production only use low-magnesium and high-calcium limestone. A large amount of high-magnesium low-grade limestone is difficult to use, resulting in a large waste of resources. If high-magnesium low-grade limestone can be used to produce volume-stable high-magnesium silicate cement clinker, it will have important practical significance for comprehensive resource utilization and engineering safety.

[0003] As my country's atmospheric nitrogen oxide emissions are increasingly strictly controlled, flue gas denitrification catalysts are increasingly widely used. It is estimated that after 2025, my country will produce 250,000 to 300,000 m3 of nitrogen oxides per year. 3 Of the waste denitration catalysts, part of them can be reused through the regeneration process, while the other part, about 50%, cannot be regenerated due to severe damage to the mechanical properties and is treated as waste. Since the denitration catalyst uses rare metal elements such as vanadium and titanium as active catalytic substances, the metal element vanadium can catalyze and accelerate the reaction of nitrogen oxides and ammonia in the exhaust gas to convert into nitrogen under certain conditions, thereby eliminating the air pollution caused by nitrogen oxides. Therefore, it is widely used in flue gas denitration catalysts. Once the catalyst containing the metal element vanadium is discarded, the vanadium in it will have a certain impact on the environment. Therefore, a large number of vanadium-containing denitration catalysts need to be treated urgently. Summary of the invention

[0004] In order to solve the problems existing in the prior art, the present invention provides a volume-stable high-magnesium Portland cement clinker, a preparation method and high-magnesium Portland cement, which solve the volume stability problem caused by using low-grade limestone to prepare high-magnesium clinker, make full use of a large amount of stockpiled low-grade high-magnesium limestone resources and rare metal elements such as vanadium in waste denitrification catalysts, and achieve the goal of obtaining volume-stable Portland cement clinker while ensuring the high-quality performance of the clinker.

[0005] The present invention is achieved in that:

[0006] A volume-stable high-magnesium silicate cement clinker, composed of the following minerals in percentage by weight: C 3 S: 45-60%, C 2 S: 15-25%, C 3 A: 5-10%, C 4 AF: 10-15%, Ca 3 Mg(SiO 4 ) 2 : 2-8%, 3MgO·V 2 O 5 : 0.1-1%.

[0007] Preferably, the raw materials of the high-magnesium silicate cement clinker include: calcium raw materials, silicon raw materials, aluminum raw materials and iron raw materials.

[0008] Further preferably, the calcium raw material is high-magnesium limestone; the silicon raw material is sandstone; the aluminum raw material is slag; and the iron raw material is iron tailings and vanadium-containing waste catalyst.

[0009] Preferably, the lime saturation ratio KH of the high-magnesium silicate cement clinker is controlled at 0.86-0.92, the silicon content SM is controlled at 0.24-0.28, and the aluminum content IM is controlled at 1.1-1.5.

[0010] Preferably, the weight percentage of MgO in the high-magnesium silicate cement clinker is 4.5-10.0%.

[0011] Preferably, the pressure steam expansion rate of the cement ground by adding an appropriate amount of gypsum to the high-magnesium silicate cement clinker is not more than 0.01%.

[0012] The method for preparing the volume-stable high-magnesium silicate cement clinker comprises the following steps:

[0013] S1, the raw materials are crushed and homogenized before batching;

[0014] S2, the raw materials after batching are ground to prepare raw meal, and the raw meal fineness is controlled at 80 micron sieve residue of 8-15%;

[0015] S3, homogenizing the raw material out of the mill;

[0016] S4, the homogenized raw material is calcined, the outlet temperature of the decomposition furnace is controlled not higher than 850°C, the apparent decomposition rate is controlled at 90-95%, and the sintering temperature is controlled at 1350-1400°C;

[0017] S5. The clinker discharged from the kiln enters the grate cooler for rapid cooling to obtain volume-stable high-magnesium silicate cement clinker.

[0018] Preferably, in step S2, the raw material fineness is controlled at 80 micron sieve residue of 8-10%.

[0019] Preferably, in step S4, the sintering temperature is controlled at 1350-1375°C.

[0020] A volume-stable high-magnesium silicate cement comprises the above-mentioned high-magnesium silicate cement clinker and gypsum, wherein the weight ratio of the high-magnesium silicate cement clinker to the gypsum is 95:5-92:8.

[0021] Preferably, the cement autoclave expansion rate is no more than 0.01%.

[0022] The main idea of ​​designing the mineral composition of the volume-stable high-magnesium silicate cement clinker of the present invention is, on the one hand, to increase iron-phase minerals and improve the solid solubility of magnesium oxide in the iron-phase minerals by adjusting the clinker rate value, thereby reducing the content of free magnesium oxide; on the other hand, the remaining free magnesium oxide in the clinker is converted into compounds at a relatively low firing temperature, thereby completely eliminating the volume expansion caused by the free magnesium oxide.

[0023] After a large number of experiments, the inventors found that by introducing vanadium-containing waste catalysts into the raw materials, under the condition of high magnesium content (clinker MgO ≥ 4%), free magnesium oxide and metal element vanadium can jointly provide a mineralizer, which can significantly reduce the clinker sintering temperature, so that the clinker can be sintered at 1350-1400°C. Under the above temperature conditions, the free magnesium oxide in the clinker and the vanadium in the waste catalyst can generate compounds, as shown in the reaction formula (1); at the same time, the presence of vanadium and magnesium can also stabilize calcium-magnesium compounds, such as Ca 3 Mg(SiO 4 ) 2 , thereby converting all the free magnesium oxide in the clinker into non-expandable magnesium-containing minerals, reducing volume expansion and improving the volume stability of high-magnesium clinker.

[0024] 3MgO+V 2 O 5 →3MgO·V 2 O 5 (1)

[0025] The aluminum ratio in high magnesium clinker rate is controlled at IM = 1.30 ± 0.20, which is significantly lower than the conventional aluminum ratio control value of 1.6, and can form more iron phase minerals C in the clinker. 4 AF, this phase mineral is a very good stabilizer for magnesium oxide in clinker. The inventors have found that 10-15% C 4AF can dissolve 4-8% MgO, and together with the MgO from low-temperature mineral compounds, the magnesium oxide content in the clinker can reach 4.5-10%, without the presence of free MgO. The pressure steam expansion rate of cement prepared from high-magnesium silicate cement clinker is no more than 0.01%, maintaining excellent volume stability.

[0026] In the preparation method provided by the present invention, the raw material fineness is controlled to be 8-15% of the 80 micron sieve residue, preferably 8-10%, so that the components of the vanadium-containing waste catalyst are more evenly distributed in the raw material, the clinker mineral reaction is more complete, and the free magnesium oxide is eliminated more thoroughly.

[0027] The firing temperature is controlled at 1350-1400°C, preferably 1350-1375°C, which can better maintain the amount of magnesium-containing compounds in the clinker. When the temperature is higher than 1400°C, some magnesium-containing minerals will decompose and re-release free magnesium oxide, causing the clinker to expand in volume.

[0028] The clinker discharged from the kiln enters the grate cooler for rapid cooling, which can ensure that the magnesium oxide in the iron phase is in a solid solution state, and this part of the solid-dissolved magnesium oxide does not form an expansion effect.

[0029] The pressure steam expansion rate of cement ground by adding appropriate amount of gypsum to high magnesium silicate cement clinker is no more than 0.01%, which is far lower than the standard requirement of no more than 0.5%, thus ensuring the volume stability of cement prepared by clinker.

[0030] The advantages and positive effects of the present invention are:

[0031] (1) The present invention proposes for the first time to introduce vanadium-containing waste catalysts into the raw materials of high-magnesium clinker to form a composite mineralization effect of magnesium and vanadium, thereby reducing the clinker sintering temperature. At the same time, magnesium compounds are formed in the clinker to stabilize calcium-magnesium compounds, reduce free magnesium oxide in the clinker, and eliminate the poor stability of cement caused by free magnesium oxide.

[0032] (2) The present invention increases the iron content in the clinker and the solid solution amount of magnesium oxide in the iron phase in the clinker by adjusting the batching rate, and combines the absorption effect of magnesium compounds on free magnesium oxide, so that when the magnesium oxide content in the clinker reaches a high level of 4.5-10%, the pressure steam expansion rate of the cement is not more than 0.01%, thereby ensuring the volume stability of the cement prepared from the clinker.

[0033] (3) The implementation of the present invention can utilize high-magnesium low-grade limestone and vanadium-containing waste catalysts on a large scale, significantly improving the comprehensive utilization rate of resources and the resource utilization rate of wastes. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is the diffraction pattern of the volume-stable high-magnesium silicate cement clinker provided in Example 1 of the present invention. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0036] Example

[0037] The embodiment of the present invention provides a method for preparing volume-stable high-magnesium silicate cement clinker, comprising the following steps:

[0038] S1, the raw materials are crushed and homogenized before entering the batching system for batching;

[0039] S2. After batching, the raw materials enter the grinding system for grinding to prepare raw meal. The raw meal fineness is controlled at 80 micron sieve residue of 8-15%;

[0040] S3, the raw material out of the mill enters the homogenization system for homogenization;

[0041] S4, the raw material after homogenization enters the preheating and precalcining system and the rotary kiln firing system for calcination, the outlet temperature of the calciner is controlled not higher than 850°C, the apparent decomposition rate is controlled at 90-95%, and the firing temperature is controlled at 1350-1400°C;

[0042] S5. The clinker discharged from the kiln enters the grate cooler for rapid cooling to obtain volume-stable high-magnesium silicate cement clinker.

[0043] The raw materials include: calcium raw materials, silicon raw materials, aluminum raw materials and iron raw materials. The calcium raw materials are preferably high-magnesium limestone; the silicon raw materials are preferably sandstone; the aluminum raw materials are preferably slag; and the iron raw materials are preferably iron tailings and vanadium-containing waste catalysts.

[0044] In Examples 1 to 5, high-magnesium silicate cement clinkers with different mineral compositions were obtained by adjusting the amounts of calcium raw materials, silicon raw materials, aluminum raw materials, iron raw materials and the amount of vanadium-containing waste catalyst introduced.

[0045] Comparative Example 1

[0046] In Comparative Example 1, except that no vanadium-containing waste catalyst was added, the amounts of other raw materials added were the same as those of Example 3.

[0047] Comparative Example 2

[0048] In Comparative Example 2, except that no vanadium-containing waste catalyst was added, the amounts of other raw materials added were the same as those of Example 4.

[0049] In the above-mentioned Examples 1-5 and Comparative Examples 1-2, the content of magnesium oxide in the clinker was determined by chemical analysis; and the different mineral compositions and free magnesium oxide content in the clinker were obtained by quantitative diffraction analysis. The diffraction pattern of the high magnesium silicate cement clinker in Example 1 is as follows: Figure 1 As shown; according to the national standard "Test method for autoclave stability of cement", the autoclave expansion rate of cement ground by adding appropriate amount of gypsum to the clinker is tested.

[0050] The raw material fineness, firing temperature, clinker mineral composition, magnesium oxide content in the clinker, free magnesium oxide content in the clinker and cement pressure steam expansion rate of Examples 1-5 of the present invention and Comparative Examples 1-2 are specifically shown in Table 1.

[0051] Table 1 Data of Examples 1-5 and Comparative Examples 1-2

[0052]

[0053] The data in Table 1 show that in Examples 1-5, as the content of 3MgO·V in the clinker increases, 2 O 5 With the increase of minerals, the clinker burning temperature is reduced from 1400℃ to 1350℃, which is significantly lower than the calcination temperature of conventional silicate cement clinker of 1450℃. 3 Mg(SiO 4 ) 2 The mineral content increases, which shows that the introduction of vanadium can stabilize calcium magnesium silicate minerals, combine more magnesium oxide into compounds, and improve the volume stability of high magnesium clinker. The free magnesium oxide content in the clinkers obtained in Examples 1-4 is less than 0.5%, and the pressure steam expansion rate of the cement prepared from the clinker is less than 0.01%, thereby obtaining a volume-stable high magnesium silicate cement clinker.

[0054] Compared with Examples 3 and 4, the raw material of Example 5 has an 80 μm sieve residue of 18%, the fineness is controlled to be coarse, and the clinker expansion rate increases to 0.015%, which is still within the normal range. This shows that the raw material fineness has a certain influence on the volume stability of the clinker. Therefore, the preferred raw material fineness of the present invention is 8-15%.

[0055] The data in Table 1 show that, compared with Examples 3 and 4, Comparative Examples 1 and 2 without adding vanadium-containing spent catalysts do not have Ca 3 Mg(SiO 4 ) 2 Minerals, due to the lack of magnesium-containing compounds, 4-5% of the magnesium oxide in the clinker still exists in a free state, which also leads to a higher cement autoclave expansion rate. The specimen of comparative example 1 was even damaged after autoclave.

[0056] The results of the above embodiments and comparative examples show that the volume-stable high-magnesium silicate cement clinker proposed by the present invention forms magnesium-containing minerals by introducing vanadium-containing waste catalysts, and at the same time increases the iron phase content in the clinker by adjusting the ingredients, eliminates free magnesium oxide in the clinker, and can maintain the volume stability of the cement.

[0057] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents, and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A volume-stable high-magnesium silicate cement clinker, characterized in that: It is composed of the following minerals in percentage by weight: C3S: 45-60%, C2S: 15-25%, C3A: 5-10%, C4AF: 10-15%, Ca3Mg(SiO4)2: 2-8%, 3MgO·V2O5: 0.1-1%.

2. The volume-stable high-magnesium silicate cement clinker according to claim 1, characterized in that: The raw materials of the high-magnesium silicate cement clinker include calcium raw materials, silicon raw materials, aluminum raw materials and iron raw materials.

3. The volume-stable high-magnesium silicate cement clinker according to claim 2, characterized in that: The calcium raw material is high-magnesium limestone; the silicon raw material is sandstone; the aluminum raw material is slag; and the iron raw material is iron tailings and vanadium-containing waste catalyst.

4. The volume-stable high-magnesium silicate cement clinker according to claim 1, characterized in that: The high-magnesium silicate cement clinker has a lime saturation ratio KH controlled at 0.86-0.92, a silicon content SM controlled at 0.24-0.28, and an aluminum content IM controlled at 1.1-1.

5.

5. The volume-stable high-magnesium silicate cement clinker according to claim 1, characterized in that: The weight percentage of MgO in the high-magnesium silicate cement clinker is 4.5-10.0%.

6. The volume-stable high-magnesium silicate cement clinker according to claim 1, characterized in that: The pressure steam expansion rate of the cement ground by adding an appropriate amount of gypsum to the high-magnesium silicate cement clinker is not more than 0.01%.

7. A method for preparing volume-stable high-magnesium silicate cement clinker according to any one of claims 1 to 6, characterized in that: The following steps are involved: S1, the raw materials are crushed and homogenized before batching; S2, the raw materials after batching are ground to prepare raw meal, and the raw meal fineness is controlled at 80 micron sieve residue of 8-15%; S3, homogenizing the raw material out of the mill; S4, the homogenized raw material is calcined, the outlet temperature of the decomposition furnace is controlled not higher than 850°C, the apparent decomposition rate is controlled at 90-95%, and the sintering temperature is controlled at 1350-1400°C; S5. The clinker discharged from the kiln enters the grate cooler for rapid cooling to obtain volume-stable high-magnesium silicate cement clinker.

8. The method for preparing volume-stable high-magnesium silicate cement clinker according to claim 7, characterized in that: In step S2, the raw material fineness is controlled at 80 micron sieve residue of 8-10%.

9. The method for preparing volume-stable high-magnesium silicate cement clinker according to claim 7, characterized in that: In step S4, the firing temperature is controlled at 1350-1375°C.

10. A volume-stable high-magnesium silicate cement, characterized in that: The invention comprises the volume-stable high-magnesium silicate cement clinker and gypsum as described in any one of claims 1 to 6, wherein the weight ratio of the high-magnesium silicate cement clinker to the gypsum is 95:5 to 92:

8.

11. The volume-stable high-magnesium silicate cement according to claim 10, characterized in that: The pressure steam expansion rate of the cement is not more than 0.01%.

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