Method for preparing alkali activator and mineral admixture by converting silicon-calcium-based solid waste material

Abstract

The invention relates to a method for preparing an alkali activator and a mineral admixture by converting a silicon-calcium-based solid waste material, which comprises the following steps: dispersing the silicon-calcium-based solid waste material in a sodium carbonate aqueous solution for reaction, and then carrying out solid-liquid separation to obtain filtrate and solid waste residues; excessive sodium carbonate is separated from the filtrate, and a silicon-rich high-alkali solution is obtained; carrying out modulus and concentration determination on the silicon-rich high-alkali solution, and adjusting the molar ratio of SiO2 to Na2O in the silicon-rich high-alkali solution to 1.0-2.0 to obtain a regenerated alkali activator; the solid waste is doped and dried, and the regenerated mineral admixture is obtained. By means of the method, the silicon-calcium-based solid waste material can be converted to generate the regenerated alkali activator and the mineral admixture, the regenerated material obtained through conversion can serve as a raw material of a cementing material, energy consumption and carbon emission are reduced, and meanwhile high-valued closed-loop utilization of the silicon-calcium-based solid waste is achieved.

Description

Technical Field

[0001] This invention relates to the field of solid waste resource utilization and green building materials technology, and more specifically, to a method for converting silicon-calcium based solid waste materials into alkali activators and mineral admixtures. Background Technology

[0002] With the continuous advancement of infrastructure construction and urban renewal, steel smelting and building demolition have generated a large amount of silicon-calcium based solid waste, including converter steel slag, electric furnace steel slag, recycled waste concrete powder, and cement kiln ash. Public research shows that typical converter steel slag generally contains more than 35% CaO and more than 10% SiO2, and also contains a certain amount of free calcium oxide and free magnesium oxide, which can be regarded as underutilized potential cementitious material resources.

[0003] Taking steel slag as an example, although its main crystalline phase is similar to that of cement clinker, its high content of free calcium oxide and free magnesium oxide makes it prone to poor volume stability when used directly as a building material, resulting in a long-term low utilization rate. It is mostly disposed of through stockpiling or low-value landfill. The preparation of recycled aggregates from waste concrete has some application in engineering, but the recycled powder portion is mostly composed of hydrated calcium silicate and calcium hydroxide, which have low activity and are often discarded. Existing utilization pathways for silicon-calcium based solid waste mostly involve single-component extraction, failing to fully realize high-value utilization of all components. Existing processes often focus on extracting silicon dioxide or specific metal elements from silicon-calcium based solid waste, but the resulting solid residue is difficult to further utilize.

[0004] Meanwhile, alkali-activated cementitious materials are considered a potential green building material system to replace silicate cement due to their low clinker consumption and excellent mechanical properties. However, the commonly used activators for this system currently include commercial water glass and sodium hydroxide, which are costly; moreover, commercial water glass is usually produced by melting quartz sand and soda ash at temperatures above 1300℃, resulting in high energy consumption and large carbon emissions. Summary of the Invention

[0005] Based on the aforementioned technical problems in the existing technology, this invention innovatively proposes a method for preparing alkali activators and mineral admixtures by converting all components of silicon-calcium-based solid waste. By converting calcium in the solid waste material into calcium carbonate and leaving it in the solid phase, the silicon component and the alkali generated in situ enter the liquid phase, and are converted into alkali activators through liquid phase conditioning. The modified solid waste residue is then used as a mineral admixture to prepare alkali-activated materials. This method achieves high-value closed-loop utilization of silicon-calcium-based solid waste while reducing energy consumption and carbon emissions.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] A method for converting silicon-calcium based solid waste materials into alkali activators and mineral admixtures includes the following steps:

[0008] S1. Disperse the silicon-calcium based solid waste material in an aqueous sodium carbonate solution, react it, and then separate the solid and liquid to obtain filtrate and solid waste residue;

[0009] S2. Separate excess sodium carbonate from the filtrate to obtain a silicon-rich, highly alkaline solution;

[0010] S3. The modulus and concentration of the silicon-rich, high-alkali solution are determined, and the molar ratio of SiO2 to Na2O in the silicon-rich, high-alkali solution is adjusted to 1.0-2.0 to obtain a regenerated alkali activator; the solid waste is dried to obtain a regenerated mineral admixture.

[0011] Calcium silicate-based solid waste materials are rich in minerals such as tricalcium silicate and dicalcium silicate. This invention utilizes the chemical instability of calcium silicate-based solid waste in concentrated sodium carbonate solution to dissolve it in sodium carbonate solution, obtaining a silicon-rich, highly alkaline solution. Taking simplified dicalcium silicate as an example, its main reaction in sodium carbonate solution can be summarized as: 2CaO·SiO2(solid) + 2Na2CO3(liquid) + H2O → 2CaCO3(solid) + Na2SiO3(liquid) + 2NaOH(liquid); some free CaO or other calcium phases can also react with sodium carbonate as follows: CaO(solid) + Na2CO3(liquid) + H2O → CaCO3(solid) + 2NaOH(liquid). Therefore, silicon enters the liquid phase in the form of sodium silicate, and calcium is enriched in the solid phase in the form of calcium carbonate. Sodium hydroxide and some unreacted sodium carbonate are present in the liquid phase, forming a highly alkaline, low-molecular-weight solution.

[0012] In some embodiments, in step S1, the concentration of the sodium carbonate aqueous solution is 1.5-3 mol / L; the solid-liquid ratio is 10-25 ml / g.

[0013] In some embodiments, the reaction temperature in step S1 is 20-55°C.

[0014] In some embodiments, in step S3, the silicon-rich alkaline solution is concentrated or silicon-based materials are added to the silicon-rich alkaline solution to adjust the solid content of the silicon-rich alkaline solution to 30-45 wt%, thereby adjusting the molar ratio of SiO2 to Na2O in the silicon-rich alkaline solution to 1.0-2.0.

[0015] In some embodiments, the siliceous material is at least one of silica fume and silica.

[0016] In some embodiments, in step S2, the filtrate is heated to 40-50°C to concentrate it to 1 / 3 to 1 / 2 of its original volume, and then cooled to 20-25°C to crystallize, and the solid and liquid are separated to obtain a silicon-rich, high-alkali solution.

[0017] In some embodiments, the silicon-calcium based solid waste material is at least one of converter steel slag powder, circuit steel slag powder, recycled waste concrete powder, and cement kiln ash.

[0018] In some embodiments, the specific surface area of ​​the silicon-calcium based solid waste material is 300-500 m². 2 / kg, with a median particle size of 5-30μm.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0020] (1) Cost and carbon emissions are significantly reduced. This invention utilizes a low-temperature wet process to convert raw materials in situ, eliminating the need for high-temperature melting above 1300℃ to prepare water glass. The raw materials are mainly silicon-calcium based solid waste and sodium carbonate, which significantly reduces the energy consumption and carbon emissions in the production of alkali activators.

[0021] (2) Closed-loop utilization of all components. The feed consists of silicon-calcium based solid waste and sodium carbonate, and the output consists of solid waste-derived alkali activator and modified solid waste micro powder. The two work synergistically in the same cementitious system, which can realize the application of high-volume solid waste and reduce the discharge of waste liquid and waste residue.

[0022] (3) Improved volume stability and shrinkage performance. Free calcium oxide and free magnesium oxide in solid waste materials are basically converted into stable carbonates, and the recycled solid waste powder passes the pressure steam stability test. A small amount of residual carbonate ions in the recycled alkali activator solution can form carboaluminate with aluminates, which helps to compensate for chemical shrinkage. Experiments show that, under the condition of meeting the strength requirements, the drying shrinkage rate is significantly lower than that when using high-modulus commercial water glass.

[0023] (4) The combination of high-alkali and low-modulus activators with in-situ generated nano-calcium carbonate nuclei is beneficial to improving the early hydration rate and strength; by adjusting the modulus and water-cement ratio, the fluidity, setting time and mechanical properties can be taken into account in different application scenarios. Attached Figure Description

[0024] Figure 1 The process flow diagram for preparing alkali activators and mineral admixtures from silicon-calcium based solid waste materials in the examples is shown.

[0025] Figure 2 The XRD diffraction patterns of converter steel slag powder before and after modification in Example 1 are shown. Detailed Implementation

[0026] Numerous specific details are set forth in the following description to provide a full understanding of the invention. However, the invention can be practiced in many other ways different from those described herein, and similar modifications can be made by those skilled in the art without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0027] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0028] General experimental conditions

[0029] (1) Mortar preparation standard: The preparation of mortar shall refer to GB / T 17671 Cement Mortar Strength Test Method.

[0030] (2) Basic mix proportion: Unless otherwise specified, the total amount of cementitious material in each test group is 450g and ISO standard sand is 1350g.

[0031] (3) Control of activator dosage and water-cement ratio: The regenerated alkali activator is a solid solution, and its total dosage is controlled according to the target water-cement ratio. The water-cement ratio is defined as the ratio of the total water consumption of the system to the total mass of the cementitious material. The total water consumption includes the water in the activator and the additional water added to adjust workability. In the examples where no additional water is added, the water-cement ratio can be approximately calculated based on the water in the activator. For example, when the solid content of the activator is 38%, to obtain a water-cement ratio of approximately 0.50, the total dosage of the activator is approximately 360g, of which approximately 225g is water. The total dosage of the activator in other examples is adjusted in the same way.

[0032] (4) Curing conditions: After the specimens are formed, they shall be cured under standard curing conditions of 20±1 ℃ and relative humidity not less than 95% until the specified age.

[0033] Example 1: Preparation of Alkali Activator and Mineral Admixture from Converter Steel Slag Powder

[0034] like Figure 1 As shown, the preparation of regenerated alkali activator and mineral admixtures from converter steel slag powder includes the following steps:

[0035] Step S1, In-situ Transformation

[0036] Converter slag powder with a specific surface area of ​​approximately 400 m² / kg and a D50 of approximately 15 μm was selected. 1000 g of the powder was dispersed in 20 L of a 2.5 mol / L sodium carbonate solution and mechanically stirred at 45 °C for 12 h. After the reaction, a slurry containing a solid-liquid mixture was obtained.

[0037] Step S2: Excess sodium carbonate recovery and solid-liquid separation

[0038] The slurry is separated by plate and frame filter press to obtain filtrate A and filter residue B. Filtrate A is heated to about 40 °C for moderate evaporation to concentrate its volume to 1 / 2 of its original volume, and then cooled to 20-25 °C to precipitate crystals mainly composed of sodium carbonate. The crystals are separated by filtration and recovered and returned to the next batch in-situ conversion step for reuse, while filtrate C is obtained.

[0039] Step S3, component conditioning

[0040] The total alkalinity of filtrate C was found to be high, with a modulus of approximately 0.8. An appropriate amount of silica fume was added to filtrate C, and it was mechanically stirred to disperse it evenly. The molar ratio of SiO2 to Na2O was adjusted to approximately 1.2, and the solid content was moderately concentrated to reach 38%, yielding regenerated alkali activator 1.

[0041] Filter residue B was dried at 105 °C and lightly ground to obtain recycled steel slag powder. The obtained recycled steel slag powder was characterized, and its XRD results are shown below. Figure 2 As shown. Figure 2 XRD analysis showed that the characteristic peak of free calcium oxide in the original steel slag powder disappeared, the peak of calcium carbonate was significantly enhanced, and the autoclaving stability test was qualified.

[0042] Step S4, Mortar Preparation and Properties

[0043] The cementitious material consisted of 30% recycled steel slag powder and 70% S95 granulated blast furnace slag powder. The dosage of recycled alkali activator 1 was controlled based on a water-cement ratio of approximately 0.50. The results are shown in Table 1. After the cementitious material was prepared by recycling alkali activator 1, recycled steel slag powder, and granulated blast furnace slag, and cured for 28 days, the compressive strength was approximately 46.8 MPa, the initial setting time was approximately 45 min, and the drying shrinkage rate was approximately 0.041%.

[0044] Example 2: Preparation of Alkali Activator and Mineral Admixture from Waste Concrete Recycled Micropowder

[0045] Step S1, In-situ Transformation

[0046] Waste concrete powder obtained by crushing and grinding C30 waste concrete has a specific surface area of ​​approximately 380 m². 2 / kg, D50 approximately 20μm. 1000g of waste concrete powder was weighed and dispersed in 15 L of sodium carbonate solution with a concentration of 2.0 mol / L. The mixture was stirred and reacted at 25℃ for 6 h to obtain a slurry containing a solid-liquid mixture.

[0047] Step S2: Excess sodium carbonate recovery and solid-liquid separation

[0048] Solid-liquid separation was performed as described in Example 1 to obtain filter residue E. The filtrate was heated and evaporated to concentrate its volume to 1 / 3 of its original volume. After cooling, solid-liquid separation was performed again to recover sodium carbonate crystals and obtain filtrate D.

[0049] Step S3, component conditioning

[0050] The pH of filtrate D was measured to be approximately 13.8, and its modulus was approximately 0.6. Silica fume was added to filtrate D to adjust the modulus to approximately 1.4, and the solid content was controlled to be approximately 35%, yielding regenerated alkali activator 2. Filter residue E was dried and lightly ground to obtain recycled waste concrete powder.

[0051] Step S4, Mortar Preparation and Properties

[0052] The cementitious material consists of 40% recycled waste concrete powder and 60% S95 granulated blast furnace slag powder. The dosage of recycled alkali activator 2 is controlled based on a water-cement ratio of approximately 0.50. As shown in Table 1, the 28-day compressive strength is approximately 38.5 MPa, the initial setting time is approximately 55 min, and the drying shrinkage rate is approximately 0.038%, making it suitable as a cementitious system for C35 grade concrete.

[0053] Example 3: Preparation of Alkali Activator and Mineral Admixture from Electric Furnace Steel Slag Powder

[0054] Step S1, In-situ Transformation

[0055] Electric arc furnace steel slag powder with a specific surface area of ​​approximately 380 m² was selected. 2 / kg, D50 approximately 18μm. 1000g of electric furnace steel slag powder was weighed and dispersed in 22 L of sodium carbonate solution with a concentration of 2.8 mol / L. The mixture was stirred and reacted at 50℃ for 10 h to obtain a slurry.

[0056] Step S2: Excess sodium carbonate recovery and solid-liquid separation

[0057] Solid-liquid separation was performed as described in Example 1 to obtain filter residue G. The filtrate was heated and evaporated to concentrate its volume to 1 / 2 of its original volume. After cooling, solid-liquid separation was performed again to recover sodium carbonate crystals and obtain filtrate F.

[0058] Step S3, component conditioning

[0059] The filtrate F has a relatively low silicon content and a modulus of approximately 0.5. Silica is added to adjust the modulus to approximately 1.5, and the solid content is controlled at 40%, yielding regenerated alkali activator 3.

[0060] After drying, the filter residue G is lightly ground to obtain recycled electric furnace steel slag powder.

[0061] Step S4, Mortar Preparation and Properties

[0062] The cementitious material consists of 30% modified electric furnace steel slag powder, 30% S95 granulated blast furnace slag powder, and 40% Class F low-calcium fly ash. The dosage of the recycled alkali activator 3 is controlled based on a water-cement ratio of approximately 0.45-0.50. As shown in Table 1, the 28-day compressive strength is approximately 35.2 MPa, and the drying shrinkage rate is approximately 0.025%, making it suitable for large-volume concrete or components with high shrinkage control requirements.

[0063] Example 4: Roadbed material with high solid waste content

[0064] Steps S1-S3: in-situ conversion, recovery of excess sodium carbonate, and component conditioning.

[0065] Regenerated alkali activator and recycled steel slag powder were prepared according to the raw materials and process of Example 1.

[0066] Step S4, Mortar Preparation and Properties

[0067] The cementitious material is composed of 50% recycled steel slag powder and 50% S95 granulated blast furnace slag powder. The dosage of recycled alkali activator is controlled based on a water-cement ratio of approximately 0.48-0.50. The 28-day compressive strength is approximately 28.6 MPa, and the drying shrinkage rate is approximately 0.032%. It is suitable for medium-to-low strength applications such as subgrade materials, pavement base courses, or non-load-bearing blocks.

[0068] To demonstrate the technical effects of the present invention, the following comparative examples are established based on the system of Example 1.

[0069] Comparative Example 1: Commercial Activator Control

[0070] The composition of the cementitious material was the same as in Example 1, consisting of 30% recycled steel slag powder and 70% slag powder. The alkali activator was a solution prepared from analytical grade water glass and sodium hydroxide, with a modulus of approximately 1.2 and a solid content of approximately 38%. The water-cement ratio was controlled at approximately 0.50. The results are shown in Table 1. The 28-day compressive strength was approximately 47.5 MPa, essentially equivalent to that of Example 1, but the drying shrinkage rate was approximately 0.065%, significantly higher than that of Example 1.

[0071] Comparative Example 2: Pure Slag Control

[0072] The cementing material was 100% S95 granulated blast furnace slag powder, and the alkali activator was the regenerated alkali activator from Example 1. The water-cement ratio was approximately 0.50. As shown in Table 1, the 28-day compressive strength was approximately 59.2 MPa, the highest among all groups, but the drying shrinkage rate was approximately 0.078%.

[0073] The results of Examples 1-4 and Comparative Examples 1-2 are shown in Table 1.

[0074] Table 1 Results of Examples 1-4 and Comparative Examples 1-3

[0075]

[0076] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0077] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the appended claims.

Claims

1. A method for preparing alkali activators and mineral admixtures by converting silicon-calcium based solid waste materials, characterized in that, Includes the following steps: S1. Disperse the silicon-calcium based solid waste material in an aqueous sodium carbonate solution, react it, and then separate the solid and liquid to obtain filtrate and solid waste residue; S2. Separate excess sodium carbonate from the filtrate to obtain a silicon-rich, highly alkaline solution; S3. The modulus and concentration of the silicon-rich, high-alkali solution are determined, and the molar ratio of SiO2 to Na2O in the silicon-rich, high-alkali solution is adjusted to 1.0-2.0 to obtain a regenerated alkali activator; the solid waste is dried to obtain a regenerated mineral admixture.

2. The method for preparing alkali activators and mineral admixtures by converting silicon-calcium based solid waste materials according to claim 1, characterized in that, In step S1, the concentration of the sodium carbonate aqueous solution is 1.5-3 mol / L; the solid-liquid ratio is 10-25 ml / g.

3. The method for preparing alkali activators and mineral admixtures by converting silicon-calcium based solid waste materials according to claim 1, characterized in that, In step S1, the reaction temperature is 20-55℃.

4. The method for preparing alkali activators and mineral admixtures by converting silicon-calcium based solid waste materials according to claim 1, characterized in that, In step S3, the silicon-rich alkaline solution is concentrated or silicon-based materials are added to the silicon-rich alkaline solution to adjust the solid content of the silicon-rich alkaline solution to 30-45 wt%, thereby adjusting the molar ratio of SiO2 to Na2O in the silicon-rich alkaline solution to 1.0-2.

0.

5. The method for preparing alkali activators and mineral admixtures by converting silicon-calcium based solid waste materials according to claim 4, characterized in that, The siliceous material is at least one of silica fume and silica.

6. The method for preparing alkali activators and mineral admixtures by converting silicon-calcium based solid waste materials according to claim 1, characterized in that, In step S2, the filtrate is heated to 40-50°C to concentrate it to 1 / 3 to 1 / 2 of its original volume, and then cooled to 20-25°C to crystallize, resulting in solid-liquid separation and a silicon-rich, high-alkali solution.

7. The method for preparing alkali activators and mineral admixtures from silicon-calcium based solid waste materials according to any one of claims 1-6, characterized in that, The silicon-calcium based solid waste material is at least one of converter steel slag powder, circuit steel slag powder, recycled waste concrete powder, and cement kiln ash.

8. The method for preparing alkali activators and mineral admixtures from silicon-calcium based solid waste materials according to claim 7, characterized in that, The specific surface area of ​​the silicon-calcium based solid waste material is 300-500 m². 2 / kg, with a median particle size of 5-30μm.

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