Method for preparing general-purpose cement by chlorination roasting of aluminosilicates

Abstract

To provide a method for preparing general-purpose cement with low carbon emission by chlorination roasting of aluminosilicates, by which sodium oxide is introduced into the cement.SOLUTION: A mixture of aluminosilicates and sodium chloride is roasted in a steam atmosphere to obtain a roasted slag, the roasted slag is further mixed with a material containing CaO and MgO and ground to prepare a raw meal mixture, the raw meal powder is subjected to oxidative calcination at a temperature not lower than 1240°C followed by rapid cooling to obtain a calcined slag, and the calcined slag is added and mixed with 0-3% of caustic alkali and ground to obtain a general-purpose cement powder. This method can produce low-carbon general-purpose cement using only aluminosilicate slag, recover valuable metals in the slag, eliminate heavy metal pollution, and have both economic and social benefits.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention is in the field of solid waste treatment and cement building materials, and in particular relates to a method for producing general-purpose cement by chlorination roasting of aluminosilicates. [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 systems, 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. Impurities such as alkali metal oxides and MgO are harmful to the production of silicate cement clinker. Meanwhile, metallurgical and mining waste residues often contain heavy metal elements that have serious environmental impacts and cannot be directly used in the production of building materials. Silicate cement clinker 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.

[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% based on Na2O) 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 objective of the present invention is to produce a low carbon footprint general purpose cement by introducing alkali metal oxides through chlorination roasting of aluminosilicates.

[0006] In order to achieve the above object, the technical means of the present invention are as follows.

[0007] A method for producing general-purpose cement by chlorination roasting of an aluminosilicate, comprising steps (1) to (3) in the following order: Step (1): Roasting a homogeneous mixture of aluminosilicate, the main chemical composition of which is SiO2 and Al2O3, and sodium chloride in a steam atmosphere, discharging the exhaust gas, and obtaining a solid roasting residue; Step (2): Mixing the roasting residue with a substance containing CaO and MgO and pulverizing the mixture to obtain powder S1, or pulverizing the roasting residue alone, washing it with water, drying it, and then uniformly mixing it with fine powder containing CaO and MgO to obtain powder S1; Step (3): The powder S1 is sufficiently oxidized and fired at a temperature of 1240°C or higher, and then rapidly cooled to obtain a fired residue S2; Step (4): Adding the calcination residue S2 to sodium hydroxide, mixing, and pulverizing to obtain cement powder, or pulverizing the calcination residue S2 and then storing it separately as an active powder composition of two-component cement, and mixing it with an aqueous solution of sodium hydroxide and / or potassium hydroxide prepared on the spot when using.

[0008] Preferably, in step (1), the flow rate of the water vapor is 60 g min -1 m -2 That's all.

[0009] Preferably, in step (1), the maximum roasting temperature is 800 to 1000°C.

[0010] Preferably, in step (1), the incubation time at the maximum roasting temperature is 1.0 hour or longer.

[0011] Preferably, in the residue obtained by oxidatively incinerating the aluminosilicate at 950°C in step (1), the mass ratio of SiO2+Al2O3+Fe2O3+CaO+MgO+Na2O+K2O exceeds 90.0%, and the masses of each component per 100 parts by mass of SiO2+Al2O3+Fe2O3+CaO+MgO+Na2O+K2O are SiO2: 49.0-82.5, Al2O3: 10.0-46.0, Fe2O3: 0-8.1, CaO: 0-5.0, MgO: 0-9.5, and Na2O+K2O: 0-12.2, respectively.

[0012] Preferably, in step (1), the aluminosilicate and sodium chloride are mixed and pulverized by any method, and the mixed powder is passed through an 80 μm square hole sieve.

[0013] Preferably, in step (1), the amount of sodium chloride is determined so that the mass ratio of SiO2 + Al2O3 to sodium chloride and aluminosilicate is 45.0% or less.

[0014] Preferably, the raw materials in step (2) are blended so as to contain 30.0 to 42.0 parts of SiO2, 10.0 to 17.0 parts of Al2O3, 0 to 6.0 parts of Fe2O3, 22.0 to 46.0 parts of CaO, 0 to 16.0 parts of MgO, and 3.1 to 8.3 parts of Na2O+K2O per 100 parts by mass of SiO2+Al2O3+Fe2O3+CaO+MgO+Na2O+K2O in the firing residue S2 obtained in step (3).

[0015] Preferably, in step (4), the blending mass of the base is determined as (NaOH+0.713KOH) / S2=0 to 3.0%.

[0016] Preferably, the exhaust gas discharged in step (1) is introduced into water, dissolved and collected, and the aqueous solution can be used to produce HCl gas or hydrochloric acid, or to recover valuable metals.

[0017] The present invention has the following beneficial effects: (1) By introducing inexpensive alkali metal oxides through the chlorination roasting of aluminosilicates, the cement produced requires little or no base activator, significantly reducing the production cost of cement. (2) The produced general-purpose cement is mainly made of aluminosilicate, which significantly reduces carbon emissions compared to silicate cement and also consumes a large amount of aluminosilicate solid slag. (3) The content of alkali metal oxides in the cement clinker produced by the present invention is as low as 3.1%, and little or no alkali (base) is required for activation, which significantly prevents alkali precipitation in cement products, improves the durability of the cement, and allows it to be used as decorative cement. (4) Through the chlorination roasting process, valuable metals in mine tailings and metallurgical slag can be recovered, and the roasting residue can also be used to produce cement, which allows them to be utilized efficiently and comprehensively. (5) Heavy metals in mine tailings and metallurgical slag can be removed by the chlorination roasting process, and the remaining heavy metals can be further utilized by using the roasting residue to produce cement, thereby realizing effective utilization of solid waste containing heavy metals and eliminating the risk of heavy metal contamination through "double insurance." (6) The exhaust gas from the chlorination roasting of aluminosilicates can be used to produce HCl gas or hydrochloric acid. DETAILED DESCRIPTION OF THE INVENTION

[0018] The present invention will be further described below with reference to specific examples, but the scope of protection of the present invention is not limited to these examples. The examples are divided into three parts: chlorination roasting, calcination of raw material mixture, and cement hydration curing.

[0019] (1) Chloride roasting The main chemical compositions used in this invention are SiO2 and Al2O3 aluminosilicates, and include two lead-zinc tailings, one gold tailing, one lithium tailing, and a mixture of eight aluminosilicate rocks. In addition to common rock-forming element oxides, metal mine tailings also contain valuable metals that are worth recovering. The mass percentage of SiO2+Al2O3+Fe2O3+CaO+MgO+Na2O+K2O in the incineration residue obtained by oxidative incineration at 950°C exceeds 90.0%, and for every 100 mass parts of SiO2+Al2O3+Fe2O3+CaO+MgO+Na2O+K2O, the mass percentages of each component are SiO2: 49.0-82.5%, Al2O3: 10.0-46.0%, Fe2O3: 0-8.1%, CaO: 0-5.0%, MgO: 0-9.5%, and Na2O+K2O: 0-12.2%. Dried aluminosilicate and sodium chloride are mixed and finely divided, and the amount of sodium chloride blended is such that the mass ratio of SiO2+Al2O3 to NaCl and aluminosilicate is 45.0% or less. The fineness of the ground mixed powder was tested using an 80 μm square-hole sieve, and all mixed powders in each example passed through the 80 μm square-hole sieve. The finely ground mixed powder was placed in a boat-shaped crucible and placed in a tubular atmosphere furnace. The temperature was raised at a rate of 5°C / min and roasted. When the temperature reached 500°C, steam introduction began. When the temperature reached 800-1000°C, a constant temperature was maintained for 1-4 hours. After that, the power was turned off, the introduction of steam was stopped, and the intake pipe was opened to air. During the roasting period, exhaust gas was introduced into the water to dissolve it. After the roasting residue had cooled to room temperature, the introduction of gas into the water from the exhaust gas pipe was stopped. The flow rate of steam introduction during the roasting period was 60 g·min -1 m -2 or more, maximum 700g·min -1 m -2 The process parameters for each example are shown in Table 1.

[0020] Table 1: Process parameters for sodium chloride roasted aluminosilicate [Table 1] aThe content of each oxide is calculated assuming that SiO2 + Al2O3 + Fe2O3 + CaO + MgO + Na2O + K2O is 100%. b Unit: g·min -1 m -2

[0021] When valuable metals and heavy metals were contained in the aluminosilicate, the chemical composition of the cooled roasting residue was analyzed. Based on the analysis results, the decomposition rate of sodium chloride for each example (roasting number) was calculated and found to be 60 to 99.8%. Most of the sodium chloride was converted to Na2O and remained in the roasting residue. The Cl ion content remaining in the roasting residue was 0.25% to 6.67%. After chlorination roasting of the metal tailings, all valuable metals were effectively removed. Valuable metals and heavy metals can be recovered by treating the exhaust gas solution through subsequent physicochemical treatment. HCl gas is generated after chlorination roasting of aluminosilicates free of valuable metals and heavy metals. The latter can be introduced into water through the exhaust gas pipe, dissolved, and purified by distillation to produce commercially available HCl gas or hydrochloric acid. The chlorination roasting effect for each example is shown in Table 2.

[0022] Table 2: Effect of chlorination roasting [Table 2]

[0023] (2) Firing the raw material mixture The roasting residue obtained in each chlorination roasting example was mixed with raw materials containing CaO and MgO and pulverized to obtain raw material mixture powder S1. Among these, roasting residue No. 7, due to its high residual chloride ion content, was milled alone, washed with water, dried, and then uniformly mixed with the other pre-milled raw material powders in a mixer. The raw materials other than the roasting residue included kaolin, analytical-grade sodium carbonate, silica (quartz powder), iron oxide, and natural dolomite powder. The chemical composition of each raw material is shown in Table 3. The mixed powder was placed in a corundum crucible and transferred to a silicon carbide muffle furnace where it was fired while heating. The heating rate was 10°C / min. The temperature was raised to 1240–1300°C, and the temperature was maintained at this constant temperature for 1, 2, and 3 hours, respectively. Immediately after the warming period, the crucible was removed from the furnace and rapidly cooled by air or water quenching to obtain fired product S2, which was primarily composed of a glass phase. Powder X-ray diffraction analysis revealed that when the same raw material mixture was fired at different temperatures for 2 and 3 hours, the phase characteristics of the clinker samples were the same, while the samples fired at 1 hour showed differences. Therefore, the actual firing time at the maximum firing temperature was set to 2 hours. The raw material formulation and maximum firing temperature for each example are shown in Table 4. S2 was pulverized to obtain a clinker powder. Chemical analysis revealed the chemical composition of S2 (SiO2 + Al2O3 + Fe2O3 + CaO + MgO + Na2O + K2O) per 100 parts by mass: SiO2: 30.0-42.0%, Al2O3: 10.0-17.0%, Fe2O3: 0-6.0%, CaO: 22.0-46.0%, MgO: 0-16.0%, and Na2O + K2O: 3.1-8.3% (Table 5).

[0024] Table 3: Chemical composition of other ingredients used in the cement raw mix (unit: wt%) [Table 3]

[0025] Table 4: Raw material composition and firing temperature of cement raw material mixture (unit: wt%) [Table 4] a The mass of roasting residue No. 7 is calculated as the sum of SiO2 + Al2O3 + TFe2O3 + CaO + MgO + Na2O + K2O contained therein. b This roasted residue was washed with water and dried before blending.

[0026] (3) Cement hydration curing S2 was crushed into powder, and NaOH and / or KOH were dissolved in the smallest amount of water possible and cooled to room temperature. The mass ratio of NaOH and / or KOH was determined as (NaOH + 0.713KOH) / S2 = 0-3.0. The alkaline solution and clinker powder were mixed and stirred for 2-5 minutes. To facilitate liquefaction of the slurry during subsequent vibration, an appropriate amount of water was added while stirring to reduce the viscosity of the slurry. The slurry was transferred to a 40x40x40 steel mold and vibrated to compact it. The mold was 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 further cured at room temperature for three, seven, and 28 days in a humid atmosphere. The unconfined compressive strength of the test blocks after different curing periods was measured. The cement paste mix and compressive strength are shown in Table 6. As can be seen from Table 6, the prepared clinker powder exhibits a certain degree of self-gelling property, i.e., it can be hardened by simply adding water, and has good compressive strength. The strength of the cement increases with increasing alkali content. The maximum compressive strength of the cement paste at 28 days was close to 100 MPa.

[0027] Table 5: Content of each rock-forming oxide and residual chlorine in the calcined material (*unit: wt%) [Table 5] *Oxide content is calculated as the content in SiO2 + Al2O3 + Fe2O3 + CaO + MgO + Na2O + K2O.

[0028] Table 6: Cement paste mix and compressive strength of paste test blocks

Table 6

Claims

1. A method for producing general-purpose cement by chlorination roasting of an aluminosilicate, comprising steps (1) to (3) in the following order: Step (1): SiO ２ and Al ２ O ３ A homogeneous mixture of aluminosilicate and sodium chloride having the chemical composition as the main component is roasted, and exhaust gas is discharged to obtain a solid roasting residue. Step (2): Mixing the roasting residue with a substance containing CaO and MgO in a predetermined amount and pulverizing the mixture to obtain powder S1, or pulverizing the roasting residue alone, washing with water, drying, and then uniformly mixing the mixture with fine powder containing CaO and MgO to obtain powder S1; Step (3): The powder S1 is oxidized and fired at a temperature of 1240°C or higher until the phase state is stabilized, and then rapidly cooled to obtain a fired residue S2; Step (4): The method is characterized in that the calcination residue S2 is mixed and pulverized with a solid strong base of sodium hydroxide and / or potassium hydroxide to obtain a general-purpose cement powder, or the calcination residue S2 is pulverized and then stored alone, and mixed with an aqueous solution of sodium hydroxide and / or potassium hydroxide when used.

2. In step (1), the flow rate of water vapor is 60 g min －１ ・m －２ The method according to claim 1, characterized in that

3. 2. The method according to claim 1, wherein in step (1), the maximum roasting temperature is 800 to 1000°C.

4. 2. The method of claim 1, wherein in step (1), the incubation time at the maximum roasting temperature is 1.0 hour or more.

5. In the residue obtained by oxidative incineration of the aluminosilicate in step (1) at 950°C, SiO ２ +Al ２ O ３ +Fe ２ O ３ +CaO+MgO+Na ２ O+K ２ The mass ratio of O exceeds 90.0% and 100 mass parts SiO ２ +Al ２ O ３ +Fe ２ O ３ +CaO+MgO+Na ２ O+K ２ The mass of each composition is SiO ２ :49.0~82.5, Al ２ O ３ :10.0~46.0, Fe ２ O ３ : 0-8.1, CaO: 0-5.0, MgO: 0-9.5, Na ２ O+K ２ 2. The method according to claim 1, wherein O is 0 to 12.

2.

6. 2. The method according to claim 1, wherein in step (1), the aluminosilicate and sodium chloride are mixed and ground by any method, and the mixed powders all pass through an 80 μm square hole sieve.

7. In step (1), the amount of sodium chloride to be added is determined by the ratio of SiO to the amount of sodium chloride and aluminosilicate. ２ +Al ２ O ３ The method according to claim 1, characterized in that the mass ratio of is determined to be 45.0% or less.

8. In the firing residue S2 obtained in step (3), 100 parts by mass of SiO ２ +Al ２ O ３ +Fe ２ O ３ +CaO+MgO+Na ２ O+K ２ The mass of each component contained in O is SiO ２ :30.0~42.0, Al ２ O ３ :10.0~17.0, Fe ２ O ３ : 0-6.0, CaO: 22.0-46.0, MgO: 0-16.0, Na ２ O+K ２ 2. The method according to claim 1, wherein the β-glucan is O: 3.1-8.

3.

9. The method according to claim 1, wherein in step (4), the mass of the base added is calculated as (NaOH + 0.713KOH) / S2 = 0 to 3.0%.

10. 2. The method according to claim 1, characterized in that the tail gas discharged in step (1) is introduced into water, dissolved and collected, and the aqueous solution is used for producing HCl gas or hydrochloric acid, or for recovering valuable metals.

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