High-alkali high-magnesium Portland cement clinker and preparation method thereof

Abstract

The invention discloses a high-alkali high-magnesium Portland cement clinker and a preparation method thereof, the alkali content in the clinker is greater than or equal to 1.5% in terms of sodium equivalent, and the alkali in the clinker exists in the form of potassium feldspar and albite; the content of magnesium oxide in the clinker is greater than or equal to 4.5%, and all magnesium oxide is dissolved in clinker minerals; the raw material of the clinker comprises a reduction synergist, the reduction synergist is electrolytic aluminum overhaul slag, and the addition proportion of the electrolytic aluminum overhaul slag accounts for 0.1-0.3% of the total raw materials. The electrolytic aluminum overhaul slag is introduced, decomposition of alkali-containing mineral phases such as RC23S12 and RC8A3 is promoted, R2AS3 feldspar minerals are formed, the content of silicate minerals is increased, and the performance of the clinker is improved; meanwhile, the melting amount of magnesium oxide in clinker minerals is increased, formation of periclase is eliminated, and expansion damage is avoided; the negative influence of alkali and magnesium on the performance of the clinker is avoided, the application range of the high-alkali and high-magnesium calcareous raw material is expanded, and efficient utilization of resources is realized.

Description

Technical Field

[0001] This invention belongs to the technical field of preparing silicate cement clinker using high-alkali, high-magnesium, and low-grade limestone, and specifically relates to a high-alkali, high-magnesium silicate cement clinker and its preparation method. Background Technology

[0002] During crustal movements, limestone is eroded by magnesium salts and alkalis, forming complex limestone deposits containing dolomite and alkali phases. The older the geological period, the more complex the formation of such limestone deposits. When high-quality limestone resources are abundant, these high-alkali, high-magnesium limestones are often discarded as waste, resulting in resource waste. With the large-scale consumption of high-quality limestone resources in cement production, enterprises are forced to face the practical problem of using high-alkali, high-magnesium limestone, which brings a series of problems to production operations and clinker quality.

[0003] High-alkali, high-magnesium limestone introduces K₂O, Na₂O, and small amounts of alkali into the clinker, which can lower the clinker firing temperature and does not harm the clinker's properties. However, when the alkali content (in sodium equivalent) exceeds 1.5%, it will react to form an alkali-containing solid solution (RC) that is harmful to the clinker's properties. 23 S 12 RC8A3 not only consumes the silicon and calcium components originally used to form clinker minerals, but also causes the clinker to have a high free calcium content, resulting in a decline in clinker quality, and at the same time leads to the formation of crusts and blockages due to cyclic enrichment.

[0004] Magnesium oxide introduced into clinker by high-alkali and high-magnesium limestone can reach 2% solid solubility in clinker minerals under conventional calcination conditions. When the magnesium oxide content exceeds this value, periclase is formed. Solidly dissolved magnesium oxide has no expansion effect, while periclase formed from free magnesium oxide hydrates very slowly in water at room temperature. Over a long period of time, periclase hydrates to form magnesium hydroxide, which expands by up to 118% in volume, causing a series of technical problems in the process and materials, such as poor cement stability.

[0005] Electrolytic aluminum overhaul slag is a type of waste generated during the electrolytic aluminum production process. It mainly includes waste cathode carbon blocks, waste refractory materials, and waste insulation materials. Waste cathode carbon blocks typically contain 30%–70% carbon, 30%–50% fluoride, and approximately 0.2% cyanide. Therefore, directly stockpiling or landfilling large quantities of electrolytic aluminum overhaul slag would seriously impact the environment and endanger human health, necessitating urgent treatment and resource utilization. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention provides a high-alkali, high-magnesium silicate cement clinker and its preparation method, which solves the problems of clinker quality decline and expansion damage caused by using high-alkali, high-magnesium limestone to prepare cement clinker, makes full use of the large stockpiled high-alkali, high-magnesium limestone resources, and significantly improves the performance of silicate cement clinker.

[0007] The present invention is achieved as follows: a high-alkali and high-magnesium silicate cement clinker, wherein the alkali content in the clinker is greater than or equal to 1.5% by sodium equivalent, and the alkali in the clinker exists in the form of potassium feldspar and sodium feldspar; the magnesium oxide content in the clinker is greater than or equal to 4.5%, and all of it is dissolved in the clinker minerals.

[0008] Preferably, the raw materials for the high-alkali, high-magnesium silicate cement clinker include a reducing synergist.

[0009] More preferably, the reducing synergist is electrolytic aluminum overhaul slag, and the addition ratio of electrolytic aluminum overhaul slag accounts for 0.1-0.3% of the total raw materials. The carbon content of the electrolytic aluminum overhaul slag is 25%-75%, and the fluoride content is 25%-55%.

[0010] More preferably, the raw materials for the high-alkali, high-magnesium silicate cement clinker also include: calcareous raw materials, siliceous raw materials, aluminous raw materials, and ferrous raw materials.

[0011] More preferably, the calcareous raw material is high-magnesium, high-alkali limestone; the siliceous raw material is sandstone; the aluminous raw material is slag; and the ferrous raw material is iron tailings.

[0012] Preferably, in the high-alkali and high-magnesium silicate cement clinker, the saturation ratio KH is controlled at 0.88-0.95, the silica ratio SM is controlled at 2.5-3.0, and the aluminum ratio IM is controlled at 1.6-2.0.

[0013] More preferably, in the high-alkali high-magnesium silicate cement clinker, the saturation ratio KH is controlled at 0.88-0.95, the silica ratio SM is controlled at 2.7-2.9, and the aluminum ratio IM is controlled at 1.7-1.9.

[0014] Preferably, the firing temperature of the high-alkali high-magnesium silicate cement clinker is 1275-1375℃.

[0015] The preparation method of the above-mentioned high-alkali and high-magnesium silicate cement clinker includes the following steps: S1. After crushing and homogenizing the calcium raw materials, silicon raw materials, aluminum raw materials and iron raw materials, they are sent to the corresponding blending warehouses. After crushing the reducing synergist, it is sent to the corresponding blending warehouses. S2. Measure the raw materials prepared in step S1 according to the set ratio. Send the measured raw materials to the raw material mill and grind them together to prepare raw material. The fineness of the raw material is controlled so that the residue on the 80-micron sieve is 12-20%. S3. The raw material exiting the mill is sent to the raw material silo for homogenization; S4. After homogenization, the raw material is preheated and then calcined. The outlet temperature of the decomposition furnace is controlled to be no higher than 820℃, and the apparent decomposition rate is controlled to be greater than 90%. The hot raw material after decomposition is put into the kiln for calcination, and the calcination temperature is controlled at 1275-1375℃. S5. The clinker exiting the kiln enters the grate cooler for rapid cooling to obtain high-alkali and high-magnesium silicate cement clinker.

[0016] Preferably, in step S2, the fineness of the raw material is controlled to have a residue of 12-18% on an 80-micron sieve.

[0017] The main design concept of the mineral composition of the high-alkali, high-magnesium silicate cement clinker of this invention is as follows: The calcium fluoride introduced through the slag from the electrolytic aluminum overhaul can lower the temperature at which the liquid phase appears, promoting clinker firing and thus reducing the volatilization of alkali in the clinker. The carbonaceous particles introduced through the slag, under low-temperature firing conditions, create a localized reducing atmosphere around the clinker particles, promoting the reaction of alkali with silicon in the clinker to form potassium feldspar and sodium feldspar, thus preventing the formation of solid solutions (RC). 23 S 12 Along with alkali-containing mineral phases such as RC8A3, the local reducing atmosphere under low-temperature conditions also increases the melting amount of magnesium oxide in clinker minerals, avoiding the formation of periclase minerals and significantly reducing the expansion damage to clinker caused by high magnesium oxide content.

[0018] To mitigate the impact of high alkali content on clinker performance, the applicant conducted extensive experimental research. Results showed that electrolytic aluminum overhaul slag, acting as a reducing synergist, can simultaneously introduce calcium fluoride and carbonaceous particles. Calcium fluoride lowers the clinker's firing temperature, reducing it from 1450℃ to 1275-1375℃. Under these temperature conditions, the carbonaceous particles generate a localized reducing atmosphere, resulting in improved RC (reducing calorific value) performance. 23 S 12 It decomposes with alkali-containing mineral phases such as RC8A3, see formula (1) and formula (2) below. The decomposed alkali reacts with silicon and aluminum under reducing atmosphere to generate feldspar minerals, see formula (3) below. At the same time, the decomposed dicalcium silicate and tricalcium aluminate increase the silicate mineral content in clinker, which helps to improve clinker performance.

[0019] (1) (2) (3) In order for the alkali to form feldspar minerals, some silicon and aluminum are required. Therefore, the silicon content (SM) in the clinker is controlled to be higher than the conventional 2.6, preferably 2.7-2.9, and the aluminum content (IM) is also appropriately increased from the conventional 1.6 to 1.7-1.9.

[0020] The applicant also observed that the solid solubility of magnesium oxide in clinker increased with the addition of electrolytic aluminum overhaul slag, which was added at a ratio of 0.1-0.3% of the raw material. Magnesium oxide in the clinker could be completely melted into the clinker minerals. The study found that the localized reducing atmosphere generated during clinker calcination by the tiny carbonaceous particles in the electrolytic aluminum overhaul slag could inhibit the formation of periclase grains and increase the melting amount of magnesium oxide in the clinker minerals. This is highly beneficial for eliminating the expansion of periclase and ensuring the volume stability of the clinker.

[0021] In the preparation method provided by the present invention, the fineness of the raw material is controlled to be 12-20% on an 80-micron sieve, preferably 12-18%, which makes the composition of the electrolytic aluminum overhaul slag more evenly distributed in the raw material, and the reaction of clinker minerals more complete, which is conducive to the formation of alkali feldspar minerals and the elimination of periclase.

[0022] The outlet temperature of the decomposition furnace is controlled to be no higher than 820℃, and the apparent decomposition rate is controlled to be greater than 90%. This is because the slag from the overhaul of electrolytic aluminum can reduce the decomposition temperature of limestone as a reducing agent. In order to avoid the decomposition furnace from forming a crust, the outlet temperature of the decomposition furnace is reduced from the conventional 900℃ to no more than 820℃. The slag from the overhaul of electrolytic aluminum can reduce the liquid phase formation temperature in the clinker as a reducing agent, thereby reducing the firing temperature. Therefore, the firing temperature is reduced from the conventional 1450℃ to 1275-1375℃. Under this temperature range and local micro-reducing atmosphere, the alkali feldspar minerals are preserved.

[0023] The advantages and positive effects of this invention are: (1) This invention is the first to propose introducing electrolytic aluminum overhaul slag into high-alkali and high-magnesium clinker raw materials to promote RC 23 S 12 The decomposition of alkali-containing mineral phases such as RC8A3 forms R2AS3 feldspar minerals, increasing the silicate mineral content and improving clinker performance; at the same time, it increases the melting amount of magnesium oxide in clinker minerals, eliminates the formation of periclase, and avoids expansion damage.

[0024] (2) By adjusting the silicon ratio and aluminum ratio, the present invention provides formation conditions for feldspar minerals, which helps the transformation of alkali minerals.

[0025] (3) The implementation of this invention can make large-scale use of high-alkali, high-magnesium, low-grade limestone and electrolytic aluminum overhaul slag solid waste, significantly improving the comprehensive utilization rate of resources and the resource utilization rate of waste. Attached Figure Description

[0026] Figure 1 The diffraction pattern is shown for the high-alkali, high-magnesium silicate cement clinker prepared in Example 1 of this invention. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0028] Example An embodiment of the present invention provides a high-alkali, high-magnesium silicate cement clinker, wherein the alkali content in the clinker is greater than or equal to 1.5% based on sodium equivalent, and the alkali in the clinker exists in the form of potassium feldspar and sodium feldspar; the magnesium oxide content in the clinker is greater than or equal to 4.5%, and is completely dissolved in the clinker minerals.

[0029] The preparation method of the above-mentioned high-alkali and high-magnesium silicate cement clinker includes the following steps: S1. After crushing and homogenizing the calcium raw materials, silicon raw materials, aluminum raw materials and iron raw materials, they are sent to the corresponding blending warehouses. After crushing the reducing synergist, it is sent to the corresponding blending warehouses. Among them, the calcareous raw material is high-magnesium and high-alkali limestone, the siliceous raw material is sandstone, the aluminous raw material is slag, the ferrous raw material is iron tailings, and the reducing enhancer is electrolytic aluminum overhaul slag. The carbon content of the electrolytic aluminum overhaul slag is 25% to 75%, and the fluoride content is 25% to 55%.

[0030] S2. Measure the raw materials prepared in step S1 according to the set ratio. Send the measured raw materials to the raw material mill and grind them together to prepare raw material. The fineness of the raw material is controlled so that the residue on the 80-micron sieve is 12-20%. Among them, the proportion of electrolytic aluminum overhaul slag added accounts for 0.1-0.3% of the total raw materials; S3. The raw material exiting the mill is sent to the raw material silo for homogenization; S4. After homogenization, the raw material is preheated and then calcined. The outlet temperature of the decomposition furnace is controlled to be no higher than 820℃, and the apparent decomposition rate is controlled to be greater than 90%. The hot raw material after decomposition is put into the kiln for calcination, and the calcination temperature is controlled to be 1275-1375℃. S5. The clinker exiting the kiln enters the grate cooler for rapid cooling to obtain high-alkali and high-magnesium silicate cement clinker.

[0031] Examples 1 to 5 obtained high-magnesium silicate cement clinker with different alkali-containing mineral compositions and magnesium oxide content by adjusting the amounts of calcareous raw materials, siliceous raw materials, aluminous raw materials, ferrous raw materials, the amount of electrolytic aluminum overhaul slag introduced, and the preparation process parameters.

[0032] Comparative Example 1 In Comparative Example 1, except for the absence of electrolytic aluminum overhaul slag, the amounts of other raw materials added were the same as those in Example 2, and the preparation process parameters were the same as those in Example 2.

[0033] In the above Examples 1-5 and Comparative Example 1, the content of magnesium oxide in clinker was determined by chemical analysis; the composition of alkali-containing minerals and the content of periclase in clinker were obtained by diffraction quantitative analysis; and the autoclaving expansion rate of cement ground after adding an appropriate amount of gypsum to clinker was tested according to the national standard "Test Method for Autoclaving Soundness of Cement".

[0034] The specific parameters of the electrolytic aluminum overhaul slag introduction amount, raw material fineness, firing temperature, alkali mineral composition in clinker, magnesium oxide content in clinker, magnesia content in clinker, and cement autoclaving expansion rate of Examples 1-5 and Comparative Example 1 are shown in Table 1 below.

[0035] Table 1 Examples and Comparative Examples

[0036] Table 1 shows that with the increase in the amount of slag introduced during the electrolytic aluminum overhaul, the NaC8A3 content in the clinker of Examples 1 and 5 was very low, and no NaC8A3 minerals were observed in Examples 2-4, thus reducing the consumption of calcium by the alkali. Meanwhile, the RAS3 content in the clinker of Examples 1-5 increased significantly, indicating that under the slightly reducing atmosphere generated by the slag during the electrolytic aluminum overhaul, the NaC8A3 minerals decomposed to form RAS3 minerals, while simultaneously releasing clinker minerals such as C2S and C3A. Compared to Example 2, Comparative Example 1, with the same alkali content, is a typical high-alkali clinker containing 21.12% NaC8A3 minerals, consuming the dicalcium silicate and tricalcium aluminate that should have formed clinker minerals.

[0037] Table 1 also shows that with the increase in the amount of electrolytic aluminum overhaul slag introduced, no periclase appeared in the clinker of Examples 1-5, resulting in very low or no autoclaving expansion of the cement (e.g., Examples 1, 2, and 5) or no expansion (Examples 3 and 4). In contrast, compared to Example 2, the periclase content in the clinker of Comparative Example 1, with the same magnesium oxide content, reached 3%, leading to clinker damage during autoclaving. This indicates that the localized reducing atmosphere generated by the electrolytic aluminum overhaul slag can inhibit the formation of periclase grains, promote the melting of magnesium oxide in the clinker minerals, and avoid autoclaving expansion damage of high-magnesium clinker.

[0038] In Examples 2-4, the residue on the 80μm sieve of the raw material was controlled at 12-18%. This not only avoided the formation of NaC8A3 minerals but also resulted in a low cooking expansion rate. This indicates that the fineness of the raw material has a certain impact on the volume stability of the clinker. Therefore, the fineness of the raw material in this invention is preferably 12-18%.

[0039] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions 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 high-alkali high-magnesia Portland cement clinker, characterized in that, The alkali content in the clinker is greater than or equal to 1.5% in terms of sodium equivalent, and the alkali in the clinker exists in the form of potassium feldspar and sodium feldspar; the magnesium oxide content in the clinker is greater than or equal to 4.5%, and is completely solid-solved in the clinker minerals.

2. The high-alkali, high-magnesia Portland cement clinker according to claim 1, characterized in that, The raw material of the high-alkali and high-magnesium silicate cement clinker comprises a reduction synergist.

3. The high-alkali, high-magnesia Portland cement clinker according to claim 2, characterized in that, The reduction synergist is electrolytic aluminum overhaul slag, and the addition proportion of the electrolytic aluminum overhaul slag accounts for 0.1-0.3% of the total raw material, the carbon content in the electrolytic aluminum overhaul slag is 25%-75%, and the fluoride content is 25%-55%.

4. The high-alkali, high-magnesia Portland cement clinker according to claim 2, characterized in that, The raw material of the high-alkali and high-magnesium silicate cement clinker further comprises calcareous raw material, siliceous raw material, aluminous raw material and ferruginous raw material.

5. The high-alkali, high-magnesia silicate cement clinker according to claim 4, characterized in that, The calcareous raw material is high-magnesium and high-alkali limestone, the siliceous raw material is sandstone, the aluminous raw material is slag, and the ferruginous raw material is iron tailings.

6. The high-alkali, high-magnesia Portland cement clinker according to claim 1, characterized in that, In the high-alkali and high-magnesium silicate cement clinker, the saturation ratio KH is controlled to be 0.88-0.95, the silicon ratio SM is controlled to be 2.5-3.0, and the aluminum ratio IM is controlled to be 1.6-2.

0.

7. The high-alkali, high-magnesia silicate cement clinker according to claim 6, characterized in that, In the high-alkali and high-magnesium silicate cement clinker, the saturation ratio KH is controlled to be 0.88-0.95, the silicon ratio SM is controlled to be 2.7-2.9, and the aluminum ratio IM is controlled to be 1.7-1.

9.

8. The high-alkali, high-magnesia Portland cement clinker according to claim 1, characterized in that, The firing temperature of the high-alkali and high-magnesium silicate cement clinker is 1275-1375 DEG C.

9. A method for the production of a high-alkali high-magnesia Portland cement clinker according to any one of claims 1 to 8, characterized in that, The method comprises the following steps: S1, crushing and homogenizing the calcareous raw material, the siliceous raw material, the aluminous raw material and the ferruginous raw material, and then sending them into corresponding blending bins, crushing the reduction synergist and then sending it into a corresponding blending bin; S2, metering the raw materials prepared in step S1 according to a set proportion, and sending the metered raw materials to a raw mill to prepare raw meal together, and controlling the fineness of the raw meal to be 12-20% of 80-micron residue; S3, sending the raw meal out of the mill to a raw meal bin for homogenization; S4, calcining the homogenized raw meal after preheating, controlling the outlet temperature of the decomposing furnace to be not higher than 820 DEG C, and controlling the apparent decomposition rate to be greater than 90%, and then putting the decomposed hot raw meal into a kiln for calcination, and controlling the firing temperature to be 1275-1375 DEG C; S5, sending the clinker out of the kiln into a grate cooler for rapid cooling to obtain the high-alkali and high-magnesium silicate cement clinker.

10. The method of producing a high-alkali high-magnesia Portland cement clinker according to claim 9, characterized by, In step S2, the fineness of the raw meal is controlled to be 12-18% of 80-micron residue.

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