A method of producing a general-purpose cement from a chloridizing roasted aluminosilicate

Abstract

The application discloses a method for preparing general-purpose cement from chloridizing roasting silico-aluminate, which comprises the following steps: firstly, roasting a mixture of silico-aluminate and sodium chloride in a water vapor atmosphere to obtain roasting slag; secondly, mixing and grinding the roasting slag with a material containing calcium oxide and magnesium oxide to prepare raw material powder; thirdly, oxidizing and calcining the raw material powder at a temperature not lower than 1240 DEG C, and then rapidly cooling to obtain calcined slag; and finally, mixing and grinding the calcined slag with 0-3% caustic soda to obtain general-purpose cement powder. The method can fully utilize silico-aluminate waste slag to prepare low-carbon general-purpose cement, and can recover valuable metals in the waste slag, eliminate heavy metal pollution, and has both economic and social benefits.

Description

Technical Field

[0001] This invention belongs to the field of solid waste treatment and cement-based building materials, and specifically relates to a method for preparing general-purpose cement from chlorinated roasted aluminosilicates. Technical Background

[0002] With economic development, the discharge of bulk solid waste is increasing. Its storage not only occupies large amounts of land but also poses serious geological disaster risks and pollutes the environment, soil, water systems, and air. Currently, the main method for effectively utilizing bulk solid waste is the preparation of building materials, including general-purpose cement. Current general-purpose cement is made from silicate cement clinker with a small amount of gypsum and other admixtures. Bulk solid waste is mostly aluminosilicates composed primarily of SiO2 and Al2O3, and the alkali metal oxides and MgO impurities it contains are harmful to the preparation of silicate cement clinker. Furthermore, metallurgical and mining waste often contains heavy metals that seriously harm the environment and cannot be directly used to prepare building materials. The high calcium and low silica-alumina chemical composition of silicate cement clinker determines that it not only has high carbon emissions but also low utilization rates for aluminosilicate waste.

[0003] Developing a general-purpose cement that is low-carbon, environmentally friendly, and has a high capacity for disposing of aluminosilicate waste to replace silicate cement has been a long-term goal for scientists in the cement field. Alkali-activated cement has outstanding advantages such as early strength, corrosion resistance, and good freeze-thaw resistance. It can make extensive use of solid waste, is low-carbon, energy-saving, and environmentally friendly, and is one of the most likely new cements to replace silicate cement. Traditional alkali-activated cement is a two-component cement that is hardened by activating active amorphous aluminosilicate (calcium) salts with strong alkali. It still has many shortcomings: (1) Kaolin resources are scarce, and the prices of other main raw materials such as fly ash and blast furnace slag have increased due to their large-scale use as admixtures in silicate cement; (2) The large amount of industrial alkali activator (accounting for 3-14 wt% based on Na2O) also keeps its cost high and is prone to efflorescence, which affects durability; (3) The inherent variability in the composition of industrial waste makes it difficult to stably control and standardize the performance and preparation process of alkali-activated cement prepared with it as the main raw material.

[0004] Reducing or eliminating the use of alkali activators can effectively lower the cost of alkali-activated cement. Patents CN110371140A and CN110451827A disclose methods for preparing and using alkali-activated cement for room temperature curing and steam curing, respectively. Both methods involve mixing and grinding a small amount of industrial alkali with potassium sodium aluminosilicate and calcareous raw materials, then calcining the mixture at 1250–1300℃ and rapidly cooling it to obtain clinker. The clinker is then finely ground and uniformly mixed with sodium silicate to produce cement. The 28-day compressive strength of their cement pastes exceeds 80 MPa and 110 MPa, respectively. While the amount of alkali activator used in these two types of cement is lower than that used in commonly used two-component alkali-activated cement, it still cannot completely eliminate the alkali activator. Summary of the Invention

[0005] The purpose of this invention is to prepare low-carbon emission general-purpose cement by introducing alkali metal oxides through chlorination and roasting of aluminosilicates.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is: a method for preparing general-purpose cement from chlorinated roasted aluminosilicates, comprising the following sequential steps:

[0007] (1) A homogeneous mixture of aluminosilicate and sodium chloride with SiO2 and Al2O3 as the main chemical components is roasted in a steam atmosphere, and flue gas is discharged to obtain solid roasting residue.

[0008] (2) The roasted residue is mixed with a substance containing CaO and MgO and ground into powder S1, or the roasted residue is ground separately, washed and dried with water, and then mixed evenly with fine powder containing CaO and MgO to obtain powder S1.

[0009] (3) Powder S1 is fully oxidized and calcined at a temperature of not less than 1240℃ and then rapidly cooled to obtain calcined slag S2;

[0010] (4) The calcined slag S2 is mixed with sodium hydroxide and ground to obtain cement powder, or the calcined slag S2 is ground and stored separately as an active powder component of two-component cement, and then mixed with freshly prepared aqueous solutions of sodium hydroxide and / or potassium hydroxide when used.

[0011] As an optimization, the water vapor flow rate in step (1) should not be less than 60 g·min. -1 ·m -2 .

[0012] As an optimization, the highest calcination temperature in step (1) is 800-1000℃.

[0013] As an optimization, the holding time at the highest calcination temperature in step (1) shall not be less than 1.0 hour.

[0014] As an optimization, in step (1), the mass percentage of SiO2+Al2O3+Fe2O3+CaO+MgO+Na2O+K2O in the residue obtained by oxidizing and calcining aluminosilicates at 950°C is greater than 90.0%; and in every 100 parts by mass of SiO2+Al2O3+Fe2O3+CaO+MgO+Na2O+K2O, the mass of each component is as follows: SiO2: 49.0~82.5, Al2O3: 10.0~46.0, Fe2O3: 0~8.1, CaO: 0~5.0, MgO: 0~9.5, Na2O+K2O: 0~12.2.

[0015] As an optimization, the aluminosilicate and sodium chloride in step (1) can be mixed and ground in any manner, and the mixed powder can pass through an 80-micron square hole sieve.

[0016] As an optimization, the amount of sodium chloride in step (1) is such that its mass ratio with SiO2+Al2O3 in aluminosilicate is no more than 45.0%.

[0017] As an optimization, the raw material formulation in step (2) should ensure that every 100 parts by mass of SiO2+Al2O3+TFe2O3+CaO+MgO+Na2O+K2O contains SiO2: 30.0-42.0 parts, Al2O3: 10.0-17.0 parts, Fe2O3: 0-6.0 parts, CaO: 22.0-46.0 parts, MgO: 0-16.0 parts, and Na2O+K2O: 3.1-8.3 parts.

[0018] As an optimization, the alkali content in step (4) is determined according to (NaOH+0.713KOH) / S2=0~3.0%.

[0019] As an optimization, the flue gas discharged in step (1) is introduced into water for dissolution and collection. The aqueous solution can be used to produce HCl gas or hydrochloric acid, or to recover valuable metals.

[0020] The present invention has the following beneficial effects:

[0021] (1) By introducing inexpensive alkali metal oxides through chlorination and roasting of aluminosilicates, the cement prepared requires little or no alkali activator, which significantly reduces the cement preparation cost.

[0022] (2) The general-purpose cement prepared uses aluminosilicate as the main raw material. Compared with silicate cement, it not only significantly reduces carbon emissions, but also can dispose of a large amount of aluminosilicate solid waste.

[0023] (3) The alkali metal oxide content in the cement clinker produced by the present invention can be as low as 3.1%, and the alkali used for activation is very little or not used, thereby significantly reducing the efflorescence phenomenon of cement products. This not only improves the durability of cement, but also allows it to be used as decorative cement.

[0024] (4) Valuable metals in mine tailings and metallurgical slag can be recovered through chlorination roasting process, and roasting slag can also be used to prepare cement, thereby achieving efficient and comprehensive utilization of them.

[0025] (5) Heavy metals in mine tailings and metallurgical slag can be removed by chlorination roasting process, and the residual heavy metals can be further solidified by preparing cement with roasting slag. While realizing the full utilization of solid waste containing heavy metals, the risk of heavy metal pollution is eliminated with "double insurance".

[0026] (6) The exhaust gas from the chlorinated roasted aluminosilicate can be used to produce HCl gas or hydrochloric acid as a byproduct. Detailed Implementation

[0027] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto. The embodiments are described in three parts: chlorination roasting, raw meal calcination, and cement hydration curing.

[0028] (1) Chlorination roasting

[0029] The aluminosilicates used in this application, whose main chemical composition is SiO2 and Al2O3, include two types of lead-zinc tailings, one type of gold tailings, one type of lithium tailings, and a mixture of eight types of aluminosilicate rocks. In addition to common rock-forming element oxides, the metal mine tailings all contain certain recoverable valuable metals. In the calcined matrix obtained by oxidizing and calcining at 950℃, the mass percentage of SiO2+Al2O3+Fe2O3+CaO+MgO+Na2O+K2O is greater than 90.0%, and the mass percentages of each component in every 100 parts by mass of SiO2+Al2O3+Fe2O3+CaO+MgO+Na2O+K2O are as follows: SiO2: 49.0–82.5%, Al2O3: 10.0–46.0%, Fe2O3: 0–8.1%, CaO: 0–5.0%, MgO: 0–9.5%, Na2O+K2O: 0–12.2%. Dry aluminosilicates and sodium chloride were mixed and ground finely. The sodium chloride content was such that the mass ratio of NaCl to SiO2+Al2O3 in the aluminosilicates was no more than 45.0%. The fineness of the ground mixed powder was tested using an 80-micron square-hole sieve; all mixed powders in each embodiment passed through the 80-micron square-hole sieve. The ground mixed powder was placed in a boat-shaped crucible in a tube furnace and calcined at a rate of 5°C / min. When the temperature reached 500°C, water vapor was introduced. When the temperature reached 800-1000°C, it was maintained at a constant temperature for 1 to 4 hours. Then, the power was turned off and the water vapor input was stopped, while the air inlet pipe was connected to the air. During calcination, the exhaust gas was introduced into water to dissolve until the calcined residue cooled to room temperature. The flow rate of water vapor introduced during calcination was no less than 60 g·min. -1 ·m -2 Up to 700g·min -1 ·m -2 The process parameters for each embodiment are detailed in Table 1.

[0030] Table 1. Summary of process parameters for sodium chloride calcination of aluminosilicates

[0031]

[0032] a The content of each oxide is calculated with SiO2+Al2O3+Fe2O3+CaO+MgO+Na2O+K2O as 100%.

[0033] b Unit: g·min -1 ·m-2

[0034] When aluminosilicates contain valence metals and heavy metals, chemical composition analysis of the cooled roasted slag was performed. The analysis results showed that the decomposition rate of sodium chloride in each embodiment (roasting number) ranged from 60% to 99.8%, with most sodium chloride being converted to Na₂O and remaining in the roasted slag. The residual Cl ion content in the roasted slag ranged from 0.25% to 6.67%. After chlorination roasting, all valence metals in the metal tailings were effectively removed. The tail gas solution could be further treated with physicochemical methods to recover valence metals and heavy metals. Aluminosilicates without valence metals and heavy metals would generate HCl gas after chlorination roasting. The HCl gas was introduced into water through the tail gas pipe and dissolved. Distillation purification could then provide commercial HCl gas or hydrochloric acid. The chlorination roasting effects of each embodiment are detailed in Table 2.

[0035] Table 2. Overview of Chlorination Roasting Effects

[0036]

[0037] (2) Raw meal calcination

[0038] The roasted residues obtained from each chlorination roasting example were mixed and ground together with raw materials containing CaO and MgO to obtain raw meal powder S1. Among them, roasted residue No. 7, due to its high chloride ion residue, was ground separately, washed with water, dried, and then mixed evenly with other pre-ground raw materials using a powder mixer. Other raw materials besides roasted residue included kaolin, analytical grade sodium carbonate, silica (quartz powder), iron oxide, and natural dolomite powder. The chemical composition of each raw material is detailed in Table 3. The mixed powder was placed in a corundum crucible and transferred into a silicon carbide muffle furnace for calcination at a heating rate of 10°C / min. When the temperature reached 1240–1300°C, it was held at a constant temperature for 1, 2, and 3 hours, respectively. After the holding time, the crucible was immediately removed from the furnace and rapidly cooled by forced air (air cooling) or water quenching (water cooling) to obtain calcined product S2, which is mainly composed of a glass phase. Analysis using powder X-ray diffraction revealed that when the isothermal time of calcination of the same raw material changed, the phase characteristics of clinker samples with isothermal time of 2 hours and 3 hours were the same, but some samples with isothermal time of 1 hour showed differences. Therefore, the highest calcination temperature and holding time used in practice were all selected as 2 hours. The raw material formulation and the highest calcination temperature of each embodiment are detailed in Table 4. S2 was finely ground to obtain calcined material (clinker) powder. Chemical analysis showed that in S2, per 100 parts by mass of SiO2+Al2O3+Fe2O3+CaO+MgO+Na2O+K2O, the proportions of each chemical component were as follows: SiO2: 30.0-42.0%, Al2O3: 10.0-17.0%, Fe2O3: 0-6.0%, CaO: 22.0-46.0%, MgO: 0-16.0%, Na2O+K2O: 3.1-8.3% (see Table 5).

[0039] Table 3 Chemical composition of other raw materials used in cement raw meal batching (unit: wt%)

[0040] <![CDATA[SiO2]]> <![CDATA[Al2O3]]> <![CDATA[TFe2O3]]> CaO MgO <![CDATA[Na2O]]> <![CDATA[K2O]]> other Kaolin 42.7 38.3 0.5 0.3 0.3 0.5 0.6 16.7 dolomite 31.6 20.2 48.3 Sodium carbonate 58.5 41.5 Calcium carbonate 56.0 44.0 quartz 99.9 0.1 iron oxide 99.9 0.1

[0041] Table 4. Summary of Cement Raw Material Proportions and Calcination Temperatures (Unit: wt%)

[0042]

[0043] a The mass of No. 7 roasted slag is calculated based on the sum of SiO2 + Al2O3 + TFe2O3 + CaO + MgO + Na2O + K2O.

[0044] b The roasting residue is washed, dried, and then used in the formulation.

[0045] (3) Cement hydration curing

[0046] S2 is ground into a fine powder. NaOH and / or KOH are dissolved in as little water as possible and cooled to room temperature. The mass of NaOH and / or KOH added is determined according to (NaOH + 0.713KOH) / S2 = 0 to 3.0. The alkaline solution is mixed with clinker powder and stirred for 2 to 5 minutes. During stirring, an appropriate amount of water is added to reduce the consistency of the slurry to facilitate liquefaction during subsequent vibration. The slurry is transferred into a 40×40×40 steel mold and vibrated to compact it. Then, the mold and the slurry are transferred into a standard cement curing chamber and cured at 20℃ and ≥90% humidity for 1 day. After curing, the cement paste specimens are demolded. If the strength after 1 day does not meet the demolding requirements, demolding is delayed. The specimens are then cured at room temperature in a humid environment for 3 days, 7 days, and 28 days. The unconfined compressive strength of the specimens at different ages is then tested. The cement paste mix design and compressive strength are detailed in Table 6. As shown in Table 6, the prepared clinker powder exhibits certain self-cementing properties, that is, it can be cured by adding water alone and has good compressive strength. With the increase of alkali content, the strength of cement shows an increasing trend, and the maximum compressive strength of cement paste after 28 days is close to 100 MPa.

[0047] Table 5. Summary of rock-forming oxide content and chlorine residue in calcined feedstock *Unit: wt%

[0048]

[0049] *Oxide content is calculated based on its content in SiO2+Al2O3+Fe2O3+CaO+MgO+Na2O+K2O

[0050] Table 6. Cement paste mix design and compressive strength of paste test blocks

[0051]

Claims

1. A method for preparing general-purpose cement from chlorinated roasted aluminosilicates, characterized in that, The steps include the following sequence: (1) A homogeneous mixture of aluminosilicates with SiO2 and Al2O3 as the main chemical components is calcined at 800~1000℃ in a steam atmosphere, and the flue gas is discharged to obtain solid calcined residue. (2) The roasting residue is quantitatively mixed with a substance containing CaO and MgO and then ground to obtain powder S1, or the roasting residue is ground separately, washed and dried, and then mixed evenly with fine powder containing CaO and MgO to obtain powder S1. (3) Powder S1 is oxidized and calcined at a temperature of not less than 1240℃ until the phase state is stable, and then rapidly cooled to obtain calcined slag S2; (4) The calcined slag S2 is mixed with solid strong alkali sodium hydroxide and / or potassium hydroxide and ground to obtain general-purpose cement powder; or the calcined slag S2 is ground and stored separately, and then mixed with an aqueous solution of sodium hydroxide and / or potassium hydroxide when used; the mass of alkali added in step (4) is calculated as (NaOH+0.713KOH) / S2=0~3.0%.

2. The method for preparing general-purpose cement from chlorinated roasted aluminosilicates as described in claim 1, characterized in that: In step (1), the flow rate of water vapor shall not be less than 60 g·min. -1 ·m -2 .

3. The method for preparing general-purpose cement from chlorinated roasted aluminosilicates as described in claim 1, characterized in that: Step (1) The holding time at the highest roasting temperature shall not be less than 1.0 hour.

4. The method for preparing general-purpose cement from chlorinated roasted aluminosilicates as described in claim 1, characterized in that: In step (1), the mass percentage of SiO2+Al2O3+Fe2O3+CaO+MgO+Na2O+K2O in the residue obtained by oxidizing and calcining the aluminosilicate at 950℃ is greater than 90.0%, and the mass of each component in each 100 mass parts of SiO2+Al2O3+Fe2O3+CaO+MgO+Na2O+K2O is as follows: SiO2: 49.0~82.5, Al2O3: 10.0~46.0, Fe2O3: 0~8.1, CaO: 0~5.0, MgO: 0~9.5, Na2O+K2O: 0~12.

2.

5. The method for preparing general-purpose cement from chlorinated roasted aluminosilicates as described in claim 1, characterized in that: In step (1), the aluminosilicate and sodium chloride are mixed and ground in any manner, and the mixed powder is passed through an 80-micron square hole sieve.

6. The method for preparing general-purpose cement from chlorinated roasted aluminosilicates as described in claim 1, characterized in that: In step (1), the amount of sodium chloride is such that its mass ratio with SiO2+Al2O3 in aluminosilicate is not greater than 45.0%.

7. The method for preparing general-purpose cement from chlorinated roasted aluminosilicates as described in claim 1, characterized in that: In the calcined slag S2 obtained in step (3), the mass of each component in 100 parts by mass of SiO2+Al2O3+Fe2O3+CaO+MgO+Na2O+K2O is as follows: SiO2: 30.0~42.0, Al2O3: 10.0~17.0, Fe2O3: 0~6.0, CaO: 22.0~46.0, MgO: 0~16.0, Na2O+K2O: 3.1-8.

3.

8. The method for preparing general-purpose cement from chlorinated roasted aluminosilicates as described in claim 1, characterized in that: Step (1) The exhaust gas is introduced into water to dissolve and collect. The aqueous solution can be used to produce HCl gas or hydrochloric acid, or to recover valuable metals.

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