A method for preparing low-carbon general-purpose cement

Abstract

The invention discloses a method for preparing low-carbon general-purpose cement. The main technical method is to grind raw materials containing silicon, aluminum, calcium, magnesium, potassium and sodium oxides into raw material powder, oxidize and calcine at a temperature not lower than 1210°C until the phase is stable, and then quench to obtain clinker; the latter is mixed with 0-3% caustic soda and ground to obtain cement powder. After the cement is hydrated, it needs to be kept moisturized at room temperature for more than 7 days. The cement is low-carbon, energy-saving, waste-recycling and environmentally friendly, and is expected to have good durability.

Description

Technical Field

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

[0002] With the development of economy, the discharge of bulk solid waste is increasing. Their storage not only occupies a large amount of land, but also poses a serious risk of geological disasters, and pollutes the environment, soil, water system and air. At present, the main method for effectively utilizing bulk solid waste is to prepare building materials, including general-purpose cement. The current general-purpose cement is made of silicate cement clinker mixed with a small amount of gypsum and other mixed materials. Bulk solid waste is mostly aluminosilicates mainly composed of SiO2 and Al2O3, and silicate cement has high carbon emissions due to its chemical composition of high calcium and low silicon and aluminum, and the utilization rate of aluminosilicate waste is not high. Moreover, the content of alkali metal oxides and MgO in many aluminosilicate wastes exceeds the standard and cannot be used to prepare silicate cement.

[0003] The research and development of low-carbon and environmentally friendly general-purpose cement with high aluminosilicate waste slag disposal capacity to replace silicate cement has been the direction that scientists in the cement field have been working towards. Alkali-activated cement has outstanding advantages such as early strength, corrosion resistance and good freeze-thaw resistance. It can make use of a large amount of solid waste slag, is low-carbon, energy-saving and environmentally friendly, and is one of the new cements that is most likely to replace silicate cement. Traditional alkali-activated cement is a two-component cement hardened by using strong alkali to activate active amorphous silicate (calcium) salts. It still has many shortcomings: (1) Kaolin resources are scarce, and other main raw materials such as fly ash and blast furnace slag have risen in price due to their large-scale use as admixtures of silicate cement; (2) The large amount of industrial alkali activator added (3-14wt% as Na2O) also makes its cost high, and it is easy to alkali-fading and affect durability; (3) The inherent variability of the composition of industrial waste slag makes it difficult to stabilize and regulate the performance and preparation process of alkali-activated cement prepared with it as the main raw material.

[0004] Reducing and eliminating the use of alkali activators can effectively reduce the cost of alkali-activated cement. Patents CN110371140A and CN110451827A disclose a method for preparing and using room temperature curing and steam curing alkali-activated cements, respectively. A small amount of industrial alkali is mixed with potassium sodium aluminosilicate and calcium raw materials, and then ground and calcined at 1250-1300°C and rapidly cooled to obtain clinker. The clinker is ground and evenly mixed with sodium water glass to obtain cement. The 28-day compressive strength of their cement pastes exceeds 80MPa and 110MPa, respectively. The amount of alkali activator used in these two types of cement is lower than that of the commonly used two-component alkali-activated cement, but it is still impossible to completely eliminate the alkali activator. Summary of the invention

[0005] The purpose of the present invention is to provide a method for preparing and using low-carbon general-purpose cement.

[0006] To achieve the above object, the present invention adopts a technical solution: a method for preparing low-carbon general-purpose cement, comprising the following steps in order:

[0007] (1) selecting raw materials whose chemical composition must contain SiO2, Al2O3, CaO, MgO, Na2O or K2O, mixing them to obtain raw materials, and grinding the dried raw materials into uniform raw material powder;

[0008] (2) The raw material powder is oxidized and calcined at a temperature not lower than 1210°C until the phase is stable and then rapidly cooled to obtain a clinker mainly composed of a glass phase;

[0009] (3) The clinker is mixed with one or both of sodium hydroxide and potassium hydroxide and then ground to obtain powdered cement, or the clinker is ground alone to obtain clinker powder, and when the cement is used, the clinker powder is mixed with an aqueous solution of one or both of sodium hydroxide and potassium hydroxide.

[0010] Preferably, the mass proportion of SiO2+Al2O3+Fe2O3+CaO+MgO+Na2O+K2O in the clinker is not less than 95%.

[0011] Preferably, in every 100 parts by mass of SiO2+Al2O3+Fe2O3+CaO+MgO+Na2O+K2O of the clinker, the masses of each component are SiO2: 31.5~45.0, Al2O3: 10.0~20.0, Fe2O3: 0~6.2, CaO: 22.0~45.0, MgO: 1.2~16.0, Na2O+K2O: 1.0~8.3.

[0012] Preferably, the chemical composition mass ratio of the clinker satisfies (CaO+MgO) / (SiO2+Al2O3)=0.6~1.0.

[0013] Preferably, the chemical composition mass ratio of the clinker satisfies SiO2 / Al2O3=2.0~4.0.

[0014] Preferably, the chemical composition mass ratio of the clinker satisfies MgO / CaO=0.04-0.66.

[0015] Preferably, the added mass of the sodium hydroxide and potassium hydroxide is determined by a mass ratio of NaOH+0.713KOH to clinker powder of 0-3.0%.

[0016] Preferably, the residue of the cement and / or clinker powder in step (3) passing through a 80-micron square hole sieve is not greater than 5%.

[0017] The method of using the universal cement is that after the cement is hydrated and formed, it must first be cured in water vapor at room temperature for no less than 7 days, and then it can be immersed in water for curing.

[0018] The present invention has the following beneficial effects:

[0019] (1) Compared with silicate cement, the calcium oxide and magnesium oxide contents in the universal cement clinker prepared by the present invention are significantly reduced, which can significantly reduce the carbon emission of cement and save non-renewable high-quality limestone resources.

[0020] (2) The general-purpose cement prepared by the present invention uses aluminosilicate as the main raw material. Compared with silicate cement, aluminosilicate waste residue can be used as the raw material in larger quantities, so the waste utilization rate is high and the sustainability is good.

[0021] (3) The alkali metal oxide content in the cement clinker prepared by the present invention can be as low as 1.0%, and little or no alkali is used for activation, thereby eliminating the efflorescence phenomenon of cement products, which not only improves the durability of cement, but also facilitates its use as decorative cement.

[0022] (4) The firing temperature of the cement clinker produced by the present invention can be as low as 1210°C, which is much lower than the firing temperature of 1450°C of silicate cement, thus achieving better energy-saving effect. DETAILED DESCRIPTION

[0023] The present invention is further described below in conjunction with specific embodiments, but the protection scope of the present invention is not limited thereto.

[0024] (1) Clinker preparation and grinding

[0025] According to the different chemical compositions, 12 kinds of potassium sodium aluminosilicate raw materials, kaolin, analytical pure sodium carbonate, calcium carbonate, silicon dioxide (quartz), iron oxide and natural dolomite were prepared. All kinds of raw materials were dried at 105°C to constant weight and then the chemical composition was detected and listed in Table 1. In the 12 embodiments, the raw materials were mixed according to the formula shown in Table 2 and then ground to obtain raw material powder, and the raw material powder reached a fineness of not more than 10% of the sieve residue on the 80-micron square hole sieve. The raw material powder was loaded into a corundum crucible and moved into a silicon carbide muffle furnace for heating and calcining. The heating rate was 10°C / minute. When the temperature was raised to 1210-1300°C, the constant temperature was maintained for 1, 2 and 3 hours respectively. After the insulation time was over, the loading crucible was immediately taken out of the furnace and rapidly cooled by blasting or quenching to obtain a clinker mainly composed of a glass phase. The clinker powder obtained by grinding the clinker had a sieve residue of not more than 5% on the 80-micron square hole sieve. Through the powder X-ray diffraction method, it was found that when the constant temperature time of the same raw material was changed, the phase characteristics of the clinker samples kept at the constant temperature for 2 hours and 3 hours were the same, but there were some differences in the samples kept at the constant temperature for 1 hour. Therefore, the constant temperature time at the highest temperature when calcining the clinker was selected to be 2 hours. The SiO2+Al2O3+Fe2O3+CaO+MgO+Na2O+K2O contained in the clinker powder is not less than 95%, and in every 100 parts by mass of SiO2+Al2O3+Fe2O3+CaO+MgO+Na2O+K2O, the masses of each component are SiO2: 31.5~45.0, Al2O3: 10.0~20.0, Fe2O3: 0~6.2, CaO: 22.0~45.0, MgO: 1.2~16.0, Na2O+K2O: 1.0~8.3, (CaO+MgO) / (SiO2+Al2O3)=0.6~1.0, SiO2 / Al2O3=2.0~4.0, MgO / CaO=0.04~0.66 (see Table 3 for details).

[0026] (2) Cement mix hydration and curing

[0027] Analytically pure NaOH and / or KOH are dissolved with as little water as possible and cooled to room temperature. The added mass of NaOH and KOH is determined by the mass ratio of (NaOH+0.713KOH) to clinker powder of 0 to 3.0. The alkaline solution is mixed with the clinker powder for 2 to 5 minutes. Water is added during stirring to reduce the consistency of the slurry so that the slurry can be liquefied during subsequent vibration. The slurry is moved into a 40×40×40 cubic steel mold for vibration compaction, and then moved into a cement standard curing box with the mold for curing at 20°C and ≧90% humidity for 1 day. After demolding, the cement slurry test block is obtained. When the strength in 1 day does not meet the demolding requirements, the demolding is delayed, and then the standard curing in moisture is continued until 7 days, and then soaked in water for curing until 28 days. The unconfined compressive strength of the test blocks at 3 days, 7 days and 28 days is tested respectively. The cement slurry ingredients and compressive strength are detailed in Table 4. As can be seen from Table 4, the prepared clinker powder exhibits a certain degree of self-gelling, that is, it can solidify and has good compressive strength by simply adding water. With the increase of alkali content, the strength of cement increases, and the maximum compressive strength of cement paste after 28 days is close to 90MPa.

[0028] Table 1 Chemical composition of raw materials Unit: wt%

[0029] Raw materials <![CDATA[SiO2]]> <![CDATA[Al2O3]]> <![CDATA[TFe2O3]]> CaO MgO <![CDATA[K2O]]> <![CDATA[Na2O]]> other Potassium Sodium Aluminosilicate 1 65.9 12.6 7.4 3.0 0.8 0.9 9.5 0.0 Potassium Sodium Aluminosilicate 2 58.1 25.7 3.9 1.5 0.4 0.5 9.8 0.0 Potassium Sodium Aluminosilicate 3 46.7 21.2 5.8 4.0 8.5 1.6 12.3 0.0 Potassium Sodium Aluminosilicate 4 69.5 10.9 2.8 1.9 0.7 1.2 13.0 0.0 Potassium Sodium Aluminosilicate 5 72.4 8.8 1.0 3.2 0.8 0.8 13.2 0.0 Potassium Sodium Aluminosilicate 6 62.5 10.4 5.6 4.4 3.7 0.8 12.6 0.0 Potassium Sodium Aluminosilicate 7 62.4 20.3 3.1 1.4 0.7 2.2 9.9 0.0 Potassium Sodium Aluminosilicate 8 72.5 13.9 0.6 1.0 0.3 0.8 11.0 0.0 Potassium Sodium Aluminosilicate 9 46.6 42.7 1.5 0.4 0.4 0.5 7.9 0.0 Potassium Sodium Aluminosilicate 10 51.6 38.7 0.6 0.3 0.3 0.3 8.2 0.0 Potassium Sodium Aluminosilicate 11 48.1 27.0 4.9 0.4 0.6 6.2 12.9 0.0 Potassium Sodium Aluminosilicate 12 49.0 37.3 0.2 0.2 0.1 0.2 13.2 0.0 Kaolin 42.7 38.3 0.5 0.3 0.3 0.6 0.5 16.7 dolomite 31.6 20.2 48.3 Sodium carbonate 58.5 41.5 Calcium carbonate 56.0 44.0 quartz 100.0 0.0 Iron Oxide 100.0 0.0

[0030] Table 2 List of cement raw material mass ratio and calcination system Unit: %

[0031]

[0032] Table 3 Chemical composition and regularity of clinker

[0033]

[0034] a The content of each oxide refers to the percentage when the sum of SiO2+Al2O3+Fe2O3+CaO+MgO+Na2O+K2O is 100%, and the others refer to the content of other chemical components in the clinker.

[0035] Table 4 Cement paste ingredients and compressive strength at different ages after curing at room temperature

[0036]

Claims

1. A method for preparing low-carbon general-purpose cement, characterized in that: The steps include the following sequence: (1) Selecting raw materials whose chemical composition must contain SiO2, Al2O3, CaO, MgO, Na2O or K2O, mixing them to obtain raw materials, and grinding the dried raw materials into uniform raw material powder; (2) The raw material powder is oxidatively calcined at a temperature not lower than 1210°C until the physical state is stable and then rapidly cooled to obtain a clinker mainly composed of a glass phase, wherein the mass proportion of SiO2+Al2O3+Fe2O3+CaO+MgO+Na2O+K2O in the clinker is not less than 95%, and in every 100 parts by mass of SiO2+Al2O3+Fe2O3+CaO+MgO+Na2O+K2O, the masses of each component are SiO2: 31.5-45.0, Al2O3: 10.0-20.0, Fe2O3: 0-6.2, CaO: 22.0-45.0, MgO: 1.2-16.0, and Na2O+K2O: 1.0-8.3; (3) Clinker is mixed with one or both of sodium hydroxide and potassium hydroxide and then ground to obtain general-purpose cement, or clinker is ground alone to obtain clinker powder, which is then mixed with an aqueous solution of one or both of sodium hydroxide and potassium hydroxide for use.

2. The method for preparing low-carbon general-purpose cement according to claim 1, characterized in that: The chemical composition mass ratio of the clinker satisfies (CaO+MgO) / (SiO2+Al2O3)=0.6~1.

0.

3. The method for preparing low-carbon general-purpose cement according to claim 1, characterized in that: The chemical composition mass ratio of the clinker satisfies SiO2 / Al2O3=2.0~4.

0.

4. The method for preparing a low-carbon general-purpose cement according to claim 1, characterized in that: The chemical composition mass ratio of the clinker satisfies MgO / CaO=0.04~0.

66.

5. The method for preparing low-carbon general-purpose cement according to claim 1, characterized in that: The rapid cooling in step (2) is blast cooling or water quenching cooling.

6. The method for preparing low-carbon general-purpose cement according to claim 1, characterized in that: The added mass of the sodium hydroxide and potassium hydroxide is determined according to the mass ratio of NaOH+0.713KOH to clinker powder being 0-3.0%.

7. The method for preparing low-carbon general-purpose cement according to claim 1, characterized in that: The mass of the cement and / or clinker powder in step (3) that passes through an 80-micron square hole sieve is no more than 5%.

Images