Method for preparing low-carbon general-purpose cement

Abstract

To provide a method for preparing a cement that is low-carbon and energy-saving, environmentally friendly by waste recycling, and that has good durability.SOLUTION: A method of the present invention for preparing a low-carbon general-purpose cement sequentially includes: a step (1) of selecting and mixing a raw material containing necessarily SiO2, Al2O3, CaO, MgO, Na2O, or K2O in the chemical composition to obtain a raw material mixture, and grinding the dried raw material mixture to obtain a uniform powder raw material mixture; a step (2) of oxidizing and calcining the powder raw material mixture at a temperature of 1210°C or more until the phase state becomes stable, followed by rapid cooling to obtain a clinker mainly composed of a glass phase; and a step (3) of mixing the clinker with one or two selected from sodium hydroxide and potassium hydroxide, and finely grinding it to obtain a general-purpose cement, wherein a compounding mass of the sodium hydroxide and the potassium hydroxide is determined such that a mass ratio of NaOH+0.713KOH to the powder clinker is 0 to 3.0%.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to the field of cement building materials, and in particular to a method for preparing low-carbon general-purpose cement. [Background technology]

[0002] With economic development, the amount of bulky solid waste generated has increased. Storage sites not only occupy vast tracts of land, but also pose serious risks to geological disasters and pollute the soil, water, and air. Currently, the most widely used method for utilizing bulky solid waste is to prepare general-purpose cement. Conventional general-purpose cement is made by mixing Portland cement clinker with small amounts of gypsum. Most bulky solid waste is an aluminosilicate composed of SiO2 and Al2O3. Portland cement has a high calcium content and low silicon and aluminum content, resulting in high carbon emissions. Furthermore, the utilization rate of aluminosilicate waste residues is low, and many aluminosilicate waste residues contain alkali metal oxides and magnesium oxide exceeding the standard, making them unsuitable for Portland cement production.

[0003] Cement scientists are striving to develop a low-carbon, environmentally friendly, and versatile cement that can utilize aluminosilicate waste residues as a Portland cement alternative. Alkali-activated cement offers excellent early strength, corrosion resistance, and freeze-thaw resistance. It can utilize large amounts of solid waste residues, making it one of the new low-carbon, energy-saving, and environmentally friendly cements. It has the greatest potential to replace Portland cement. However, conventional alkali-activated cement is a two-component cement that hardens by activating activated amorphous aluminosilicate (calcium) salts with strong alkali. It has the following drawbacks: (1) Kaolin resources are scarce, and other primary raw materials, such as fly ash and blast furnace slag, are widely used as Portland cement admixtures, driving up their prices. (2) The high usage of industrial alkali activators (3–14 wt% on a Na2O basis) increases costs and leads to alkalinity, which impacts durability. (3) The inherent composition of industrial waste residues varies, making it difficult to consistently regulate and standardize the properties and manufacturing process of alkali-activated cement produced using them as the primary raw material.

[0004] Reducing or eliminating the use of alkali activators can effectively reduce the cost of alkali-activated cement. Patents CN110371140A and CN110451827A disclose the preparation and use of ambient-cured and steam-cured alkali-activated cements, respectively. These cements are produced by mixing and grinding sodium potassium aluminosilicate and calcium raw materials, firing them at 1250-1300°C, quenching them to obtain clinker, finely grinding the clinker, and uniformly mixing it with water glass. The compressive strength of the cement paste at 28 days exceeds 80 MPa and 110 MPa, respectively. Although the amount of alkali activator used in these two cements is less than that used in conventional two-component alkali-activated cements, it is not possible to completely eliminate the alkali activator. Summary of the Invention

[0005] The present invention aims to provide a method for preparing low-carbon general-purpose cement that significantly reduces the carbon footprint of cement, conserves non-renewable high-quality limestone resources, and uses little or no alkali for activation.

[0006] The object of the present invention is achieved by the following technical solutions. 1. A method for preparing a low carbon general purpose cement, comprising the steps of: Step (1): Select and mix one or more raw materials to obtain a raw material mixture whose chemical composition must contain SiO2, Al2O3, CaO, MgO, Na2O, or K2O, and pulverize the dried raw material mixture to obtain a uniform powder raw material mixture; Step (2): The powder raw material mixture is oxidized and fired at a temperature of 1210°C or higher until the phase state is stabilized, and then rapidly cooled to obtain clinker with a glass phase as the main component. In the clinker, the mass ratio of SiO2 + Al2O3 + Fe2O3 + CaO + MgO + Na2O + K2O is 93% or more, In 100 parts by mass of the clinker, SiO2+Al2O3+Fe2O3+CaO+MgO+Na2O+K2O, the masses of each component are SiO2: 31.5 to 44.8, Al2O3: 6.1 to 19.9, Fe2O3: 0 to 6.2, CaO: 22.5 to 45.0, MgO: 1.2 to 16.0, and Na2O+K2O: 1.0 to 8.3, Step (3): Mix and finely grind one or two of the clinker, sodium hydroxide, and potassium hydroxide to obtain general-purpose cement, or finely grind the clinker alone to obtain clinker powder, which is then mixed with an aqueous solution of one or two of the clinker powder, sodium hydroxide, and potassium hydroxide when used; The blending mass of the sodium hydroxide and potassium hydroxide is determined so that the ratio of NaOH+0.713KOH to the powdered clinker is 0 to 3.0%.

[0007] Preferably, the mass ratio of the chemical composition of the clinker satisfies the following formula: (CaO+MgO) / (SiO2+Al2O3)=0.6~1.0

[0008] Preferably, the mass ratio of the chemical composition of the clinker satisfies the following formula: SiO2 / Al2O3=2.0~7.0

[0009] Preferably, the mass ratio of the chemical composition of the clinker satisfies the following formula: MgO / CaO=0.03~0.66

[0010] Specifically, in step (2), the rapid cooling is air cooling or water quench cooling.

[0011] Preferably, in step (3), the sieve residue of the general-purpose cement and the clinker powder after passing them through a 75 μm square-hole sieve is 5% or less.

[0012] Preferably, after the general-purpose cement has been hydrated and molded, it is cured in steam at room temperature for 7 days or more, and then immersed in water for further curing. [Effects of the Invention]

[0013] Compared with the prior art, the present invention has the following beneficial effects: (1) Compared with Portland cement, the calcium oxide and magnesium oxide contents in the clinker of the general-purpose cement prepared by the present invention are significantly reduced, which significantly reduces the carbon emissions of the cement and saves non-renewable high-quality limestone resources. (2) The general-purpose cement produced by the method of the present invention uses aluminosilicate as its main raw material. Therefore, compared with Portland cement, a large amount of aluminosilicate waste residue can be used as a raw material, resulting in a higher waste utilization rate and better sustainability. (3) The clinker produced by the method of the present invention has an alkali metal oxide content as low as 1.0% and requires little or no alkali activator, eliminating the efflorescence phenomenon of cement products, which improves the durability and accelerates curing, and may be used as decorative cement. (4) The firing temperature of the clinker produced by the method of the present invention is as low as 1210°C, which is much lower than the firing temperature of Portland cement, 1450°C, and therefore has a high energy-saving effect. DETAILED DESCRIPTION OF THE INVENTION

[0014] The present invention will be further described below with reference to examples, but the scope of protection of the present invention is not limited thereto.

[0015] (1) Preparation and crushing of clinker Twelve types of aluminum potassium sodium silicate raw materials, as shown in Table 1, and kaolin, sodium carbonate, calcium carbonate, silica (quartz), iron oxide, and natural dolomite of analytical purity were prepared according to their chemical compositions. Each raw material was dried at 105°C to a constant weight, and then its chemical composition was determined. The results are shown in Table 1. In 14 examples, the raw materials were mixed and pulverized according to the formulation shown in Table 2 to obtain a powder raw material mixture. All of the powder raw material mixtures were fine enough to have a sieve residue of 10% or less on a 75 μm square aperture sieve. The powder raw material mixture was placed in a corundum crucible, transferred to a silicon carbide muffle furnace, heated, and fired. The temperature was raised at a rate of 10°C / min until the temperature reached 1210-1350°C, and then maintained for 1, 2, and 3 hours, respectively. Immediately after the holding time, the crucible was removed from the furnace and rapidly cooled by blast cooling or water cooling to obtain a clinker consisting primarily of a glass phase. The clinker was then finely pulverized to obtain a powdered clinker. The sieve residue of the powdered clinker on a 75 μm square-hole sieve is 5% or less. Powder X-ray diffraction analysis revealed that when the same raw material mixture is kept at the maximum firing temperature for different periods, the phase characteristics of the clinker samples kept at the maximum temperature for 2 and 3 hours are the same, but the phase characteristics of the clinker sample kept at the maximum temperature for 1 hour are different. Therefore, when burning clinker, the maximum temperature is kept at the maximum temperature for 2 hours. The content of SiO2 + Al2O3 + Fe2O3 + CaO + MgO + Na2O + K2O in the clinker powder is 93% or more. In 100 parts by mass of SiO2 + Al2O3 + Fe2O3 + CaO + MgO + Na2O + K2O, the masses of each component are SiO2: 31.5-44.8, Al2O3: 6.1-19.9, Fe2O3: 0-6.2, CaO: 22.5-45.0, MgO: 1.2-16.0, Na2O + K2O: 1.0-8.3, respectively. Therefore, (CaO + MgO) / (SiO2 + Al2O3) = 0.6-1.0, SiO2 / Al2O3 = 2.0-7.0, and MgO / CaO = 0.03-0.66 (see Table 3).

[0016] Table 1: List of chemical composition of each raw material in the raw material mixture (unit: wt%) [Table 1] TFe2O3 refers to the sum of iron in different valence states converted into equal amounts of Fe2O3.

[0017] Table 2: Mass ratios of each raw material in the cement raw material mixture and firing temperatures (unit: %) [Table 2]

[0018] [Table 3] a The content of each oxide is expressed as a percentage when the total of SiO2 + Al2O3 + Fe2O3 + CaO + MgO + Na2O + K2O is taken as 100%. Others indicate the content of other chemical components in the clinker.

[0019] (2) Hydration and curing of cement mix The NaOH and / or KOH for analysis was dissolved in the smallest amount of water possible and cooled to room temperature. The mass ratio of NaOH and KOH to powdered clinker (NaOH + 0.713KOH) was determined to be 0-3.0. The alkaline solution and powdered clinker were mixed and stirred for 2-5 minutes. Water was added during stirring to reduce the consistency of the slurry so that it could be liquefied during subsequent vibration. The slurry was then transferred to a 40x40x40 cubic steel mold and vibrated to compact it. The mold and the mold were then transferred to a standard cement curing box and cured at 20°C and ≥90% humidity for one day before being demolded to obtain cement paste test blocks. If the strength after one day of curing did not meet the demolding requirements, demolding was delayed and the blocks were subjected to standard humidity curing for seven days, followed by water immersion curing for 28 days. The unconfined compressive strength of the test blocks was measured on days 3, 7, and 28, respectively. The cement paste mix proportions and compressive strengths are shown in Table 4. As can be seen from Table 4, the prepared powdered clinker exhibits a certain degree of self-gelling properties, meaning that it can harden simply by adding water and has good compressive strength. As the mix proportion increases, the strength of the cement increases. The maximum compressive strength of the cement paste at 28 days was close to 106 MPa.

[0020] Table 4: Cement paste mix parameters and compressive strength for different periods of room temperature curing [Table 4]

Claims

1. 1. A method for preparing a low carbon general purpose cement, comprising the steps of: Step (1): Select and mix one or more raw materials to ensure that the chemical composition contains SiO ２ , Al ２ O ３ , CaO, MgO, Na ２ O or K ２ obtaining a raw material mixture containing O; obtaining the raw material mixture; and pulverizing the dried raw material mixture to obtain a uniform powder raw material mixture; Step (2): The powder raw material mixture is oxidized and fired at a temperature of 1210°C or higher until the phase state is stabilized, and then rapidly cooled to obtain clinker mainly composed of a glass phase; In the clinker, SiO ２ +Al ２ O ３ +Fe ２ O ３ +CaO+MgO+Na ２ O+K ２ The mass proportion of O is 93% or more, 100 parts by mass of SiO in the clinker ２ +Al ２ O ３ +Fe ２ O ３ +CaO+MgO+Na ２ O+K ２ In O, the mass of each component is SiO ２ :31.5~44.8, Al ２ O ３ :6.1~19.9, Fe ２ O ３ : 0-6.2, CaO: 22.5-45.0, MgO: 1.2-16.0, Na ２ O+K ２ O: 1.0 to 8.3, Step (3): Mix and finely grind one or two of clinker, sodium hydroxide, and potassium hydroxide to obtain general-purpose cement, or finely grind the clinker alone to obtain clinker powder, which is then mixed with an aqueous solution of one or two of the clinker powder, sodium hydroxide, and potassium hydroxide when used; The blending mass of the sodium hydroxide and potassium hydroxide is determined so that the mass ratio of NaOH + 0.713KOH to powdered clinker is 0 to 3.0%. A method for preparing a low-carbon general-purpose cement, comprising:

2. The mass ratio of the chemical composition of the clinker satisfies the following formula: (CaO+MgO) / (SiO ２ +Al ２ O ３ )=0.6~1.0 2. The method for preparing a low-carbon general-purpose cement according to claim 1.

3. The mass ratio of the chemical composition of the clinker satisfies the following formula: SiO ２ / Al ２ Oh ３ =2.~7.0 2. The method for preparing a low-carbon general-purpose cement according to claim 1.

4. The mass ratio of the chemical composition of the clinker satisfies the following formula: MgO / CaO=0.03~0.66 2. The method for preparing a low-carbon general-purpose cement according to claim 1.

5. In step (2), the rapid cooling is blow cooling or water quench cooling.

2. The method for preparing a low-carbon general-purpose cement according to claim 1.

6. In step (3), the sieve residue after the general-purpose cement and the powdered clinker pass through a 75 μm square hole sieve is 5% or less.

2. The method for preparing a low-carbon general-purpose cement according to claim 1.

7. After the general-purpose cement is hydrated and molded, it is cured in steam at room temperature for 7 days or more, and then immersed in water for curing.

2. The method for preparing a low-carbon general-purpose cement according to claim 1.

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