A method for calcium-rich solid waste carbonization pretreatment for paste filling

Abstract

The application discloses a kind of calcium-rich solid waste carbonization pretreatment methods for paste filling, it is related to carbonization processing technical field, including calcium-rich solid waste with heavy metal and magnesium source are mixed;Into the gas containing CO2 in solid-liquid mixed system, maintain pH value during reaction process 7.0~8.5;Textile type calcium carbonate whisker is generated by carbonization reaction;The carbonization product obtained containing textile whisker is used to prepare paste filling material.The application generates carbonization product with textile type calcium carbonate whisker as main phase, and the micro-muscle material effect of textile whisker significantly improves the bending strength, toughness and crack resistance of paste filling body;The chemical bonding level solidification of heavy metal significantly reduces the leaching risk, meets environmental protection standard;Carbonization product can replace cement at high proportion, reduces filling cost and carbon emission, has good compatibility with existing filling production line, widens the safe resource utilization approach of calcium-rich solid waste containing heavy metal, provides integrated technical scheme for green low-carbon paste filling.

Description

Technical Field

[0001] This invention relates to the field of carbonization treatment technology, and in particular to a carbonization pretreatment method for calcium-rich solid waste used in paste filling. Background Technology

[0002] Paste backfilling technology is an important component of green coal mining. By mixing industrial solid waste such as coal gangue and fly ash with cementing materials to prepare a paste, which is then filled into the goaf, surface subsidence can be effectively controlled and large-scale solid waste disposal can be achieved. Traditional paste backfilling materials use cement as the cementing core. Cement production has high carbon emissions and costs, and the backfill itself has limited carbon sequestration capacity, making it difficult to meet the increasingly urgent low-carbon transformation needs of the coal industry. Research on utilizing calcium-rich industrial solid waste (such as carbide slag, steel slag, incineration fly ash, and calcium silicate slag) for CO2 mineralization and sequestration and as a component of backfilling materials has received widespread attention. These solid wastes contain large amounts of Ca(OH)2 or CaO, which can react with CO2 to generate stable calcium carbonate, achieving permanent carbon sequestration. In existing technologies, the carbonization treatment of calcium-rich solid waste usually adopts wet slurry carbonation or dry gas-based carbonation, with the product being calcite-type carbonate. Calcium-rich solid waste, after carbonization, can be used as a cement substitute in the preparation of paste-like fillers, both fixing carbon and reducing cement usage. However, existing technologies have the following prominent problems: First, the carbonization products have a single crystal form, limiting their enhancement of the mechanical properties of the fillers; second, calcium-rich solid waste often contains heavy metals such as lead, cadmium, chromium, and arsenic. While conventional carbonization processes can reduce their leaching toxicity to some extent, these heavy metals mainly exist in the form of surface adsorption or physical encapsulation, resulting in insufficient long-term stability and a risk of secondary pollution; third, existing carbonization processes lack targeted control over reaction conditions (temperature, pH, ionic environment), failing to fully utilize the synergistic relationship between calcium carbonate crystal transformation and heavy metal lattice substitution. Studies have shown that aragonite-type calcium carbonate whiskers, with their high aspect ratio and orthorhombic crystal structure, can not only play a toughening role as micro-reinforcing materials, but their lattice also effectively resists square heavy metal ions (such as Pb). 2+ Cd 2+ It has a higher capacity and can achieve chemical bonding level solidification. However, there are no reports in the existing technology of simultaneously applying the directional synthesis of aragonite whiskers and the solidification of heavy metal lattices to the carbonization pretreatment of calcium-rich solid waste and using it for paste filling.

[0003] However, current common solutions have many drawbacks, including: existing carbonization products are mainly calcite, which can only play a physical filling role and cannot effectively improve the flexural strength and toughness of the filling body, resulting in limited cement replacement rate; heavy metal solidification is mainly based on surface adsorption or physical encapsulation, which has poor long-term stability and is prone to secondary leaching in acidic environments; the advantages of aragonite whiskers in lattice accommodation of heavy metals are not utilized, and there is a lack of synergistic process of whisker toughening and heavy metal chemical solidification; the carbonization reaction conditions are crude and lack targeted control over crystal form and heavy metal substitution; the carbonization products have low gelling activity, making it difficult to achieve a high proportion of cement replacement. Summary of the Invention

[0004] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0005] In view of the problems existing in the current method for carbonization pretreatment of calcium-rich solid waste used for paste filling, the present invention is proposed.

[0006] Therefore, the purpose of this invention is to provide a pretreatment method for carbonization of calcium-rich solid waste for paste filling. This method addresses the problems of existing technologies where carbonization products are mainly calcite, which can only play a physical filling role and cannot effectively improve the flexural strength and toughness of the filling body, thus limiting the cement replacement rate; heavy metal solidification is mainly based on surface adsorption or physical encapsulation, resulting in poor long-term stability and easy secondary leaching in acidic environments; the advantages of aragonite whiskers in lattice accommodation of heavy metals are not utilized, and there is a lack of synergistic process between whisker toughening and heavy metal chemical solidification; the carbonization reaction conditions are crude, lacking targeted control over crystal form and heavy metal substitution; and the carbonization products have low gelling activity, making it difficult to achieve a high proportion of cement replacement.

[0007] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0008] In a first aspect, embodiments of the present invention provide a method for carbonization pretreatment of calcium-rich solid waste for paste filling, comprising mixing calcium-rich solid waste containing heavy metals with a magnesium source and preparing a solid-liquid mixture system; introducing a gas containing CO2 into the solid-liquid mixture system and carrying out a carbonization reaction at a temperature of 60~95°C, maintaining a pH value of 7.0~8.5 during the reaction; generating aragonite-type calcium carbonate whiskers through the carbonization reaction, wherein the aspect ratio of the aragonite-type whiskers is ≥10:1, and the heavy metal ions in the solid waste are embedded in the aragonite lattice through lattice substitution; and using the obtained carbonization product containing aragonite whiskers to prepare paste filling materials.

[0009] As a preferred embodiment of the pretreatment method for carbonization of calcium-rich solid waste for paste filling according to the present invention, the calcium-rich solid waste is at least one of carbide slag, steel slag, incineration fly ash or calcium silicate slag.

[0010] As a preferred embodiment of the carbonization pretreatment method for calcium-rich solid waste used for paste filling according to the present invention, wherein: the magnesium source is at least one of magnesium chloride, magnesium sulfate or magnesium oxide; the magnesium source is dry premixed with the calcium-rich solid waste before solid-liquid mixing.

[0011] As a preferred embodiment of the pretreatment method for carbonization of calcium-rich solid waste for paste filling according to the present invention, wherein: the liquid in the solid-liquid mixture is water or recycled filtrate; a crystal form regulator is added to the solid-liquid mixture, and the crystal form regulator is at least one of sodium citrate, sodium tartrate or disodium ethylenediaminetetraacetate.

[0012] As a preferred embodiment of the carbonization pretreatment method for calcium-rich solid waste used for paste filling according to the present invention, the carbonization reaction is accompanied by stirring.

[0013] As a preferred embodiment of the pretreatment method for carbonization of calcium-rich solid waste for paste filling according to the present invention, wherein: the introduced CO2 gas is industrial tail gas or high-purity CO2; the CO2 is introduced in the form of microbubbles through a gas distributor.

[0014] As a preferred embodiment of the pretreatment method for carbonization of calcium-rich solid waste for paste filling according to the present invention, wherein: during the reaction process, the pH value is maintained at 7.0~8.5 by automatically adding alkaline solution or acid solution; and the change in conductivity of the reaction system is monitored to determine the endpoint of the carbonization reaction.

[0015] As a preferred embodiment of the pretreatment method for carbonization of calcium-rich solid waste used for paste filling according to the present invention, wherein: the aragonite whiskers are the main crystalline phase of the carbonization product.

[0016] As a preferred embodiment of the carbonization pretreatment method for calcium-rich solid waste used for paste filling according to the present invention, the heavy metal includes at least one of lead, cadmium, chromium, and arsenic.

[0017] As a preferred embodiment of the pretreatment method for carbonization of calcium-rich solid waste for paste filling according to the present invention, the carbonization product is used to replace part of the cement to prepare paste filling material.

[0018] The beneficial effects of this invention are as follows: This invention mixes calcium-rich solid waste containing heavy metals with a magnesium source and introduces CO2 at 60~95℃ and pH 7.0~8.5 to carry out a carbonization reaction, generating a carbonization product with aragonite-type calcium carbonate whiskers as the main phase (length-to-diameter ratio ≥10:1). At the same time, heavy metal ions are inserted into the aragonite lattice through lattice substitution, achieving multiple beneficial effects: the micro-reinforcing effect of aragonite whiskers significantly improves the flexural strength, toughness, and crack resistance of the paste filling body; the chemical bonding and solidification of heavy metals greatly reduces the leaching risk and meets environmental protection standards; the carbonization product can replace cement in a high proportion (≥40%), reducing filling costs and carbon emissions, and the process conditions are precisely controllable, with good compatibility with existing filling production lines, broadening the safe resource utilization pathways for calcium-rich solid waste containing heavy metals, and providing an integrated technical solution for green and low-carbon paste filling. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein:

[0020] Figure 1 This is a flowchart illustrating the implementation of the present invention in Example 1. Detailed Implementation

[0021] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0022] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0023] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0024] Example 1

[0025] Reference Figure 1 This is the first embodiment of the present invention, which provides a method for carbonization pretreatment of calcium-rich solid waste for paste filling, comprising the following steps:

[0026] S1: Mix calcium-rich solid waste containing heavy metals with a magnesium source and prepare a solid-liquid mixture system.

[0027] Preferably, the calcium-rich solid waste is at least one of carbide slag, steel slag, incineration fly ash, or calcium silicate slag.

[0028] Furthermore, the magnesium source is at least one of magnesium chloride, magnesium sulfate, or magnesium oxide; the magnesium source is dry-premixed with calcium-rich solid waste before solid-liquid mixing.

[0029] Furthermore, the liquid in the solid-liquid mixture is water or recycled filtrate; a crystal form regulator is added to the solid-liquid mixture, which is at least one of sodium citrate, sodium tartrate, or disodium ethylenediaminetetraacetate.

[0030] Specifically, heavy metals include at least one of lead, cadmium, chromium, and arsenic.

[0031] Furthermore, in the solid-liquid mixture system, the solid-liquid ratio is 1:3 to 1:5 (mass ratio).

[0032] Specifically, the mixing time for dry premixing is 5 to 15 minutes, so that the magnesium source is evenly dispersed in the calcium-rich solid waste.

[0033] Furthermore, the amount of crystal form regulator added is 0.05% to 0.5% of the mass of calcium-rich solid waste.

[0034] Preferably, the magnesium source is premixed with calcium-rich solid waste using a dry method to ensure the presence of magnesium. 2+ Uniformly dispersed on the particle surface, it provides heterogeneous nucleation sites for aragonite whiskers and inhibits calcite formation; simultaneously, the addition of crystal morphology modifiers (such as sodium citrate) can complex Ca... 2+ By regulating supersaturation and promoting one-dimensional crystal growth, it can form soluble complexes with heavy metal ions to slow down their precipitation rate, allowing them to preferentially enter the crystal lattice during subsequent carbonization and crystallization. The appropriate solid-liquid ratio (1:3~1:5) and filtrate recycling not only ensure mass transfer efficiency and reaction sufficiency, but also achieve zero water discharge and reduce environmental impact.

[0035] For example, carbide slag is selected as a calcium-rich solid waste containing lead and cadmium heavy metals, and magnesium chloride is used as a magnesium source. The two are first dry-premixed for 10 minutes to make magnesium chloride evenly dispersed on the surface of carbide slag particles. Then water is added as liquid, and a solid-liquid mixture is prepared at a mass ratio of 1:4. At the same time, sodium citrate of 0.2% of the mass of carbide slag is added as a crystal form regulator to complete the preparation of the solid-liquid mixture system, which prepares the initial stage for the subsequent carbonization reaction.

[0036] S2: Introduce CO2-containing gas into the solid-liquid mixture and carry out a carbonization reaction at a temperature of 60~95℃, while maintaining the pH value at 7.0~8.5 during the reaction.

[0037] Preferably, the introduced CO2 gas is industrial exhaust gas or high-purity CO2; the CO2 is introduced in the form of microbubbles through a gas distributor.

[0038] Specifically, during the reaction, the pH value is maintained at 7.0~8.5 by automatically adding alkaline or acidic solutions; the change in conductivity of the reaction system is monitored to determine the endpoint of the carbonization reaction.

[0039] Furthermore, the carbonization reaction takes 30 to 120 minutes.

[0040] Specifically, the stirring speed is 200~500 rpm to maintain the solid-liquid suspension state.

[0041] Furthermore, the CO2 ventilation rate is 0.2~2.0 L / minperL reaction volume.

[0042] Specifically, the alkaline solution is a 0.1~1.0M sodium hydroxide solution, and the acid solution is a 0.1~1.0M dilute hydrochloric acid solution.

[0043] Furthermore, the carbonization reaction is considered complete when the rate of decrease in conductivity is less than 20% of the initial rate.

[0044] Preferably, the carbonization reaction is carried out within a temperature range of 60~95℃, which provides a thermodynamically advantageous window for the growth of aragonite whiskers. Combined with precise maintenance of pH 7.0~8.5, CO3 can be effectively controlled. 2- / HCO3 - The ratio and CaCO3 supersaturation are controlled to avoid calcite precipitation caused by rapid homogeneous nucleation; the introduction of CO2 in the form of microbubbles significantly increases the gas-liquid contact area and improves carbonization efficiency. At the same time, the reaction endpoint is determined by real-time monitoring of conductivity (the rate of decline is less than 20% of the initial value), which can prevent excessive carbonization from causing whisker dissolution or crystal transformation, and ensure the crystal form and batch stability of the product.

[0045] For example, CO2 from industrial exhaust gas is introduced into the prepared solid-liquid mixture. The CO2 is introduced in the form of microbubbles through a gas distributor at a rate of 1.0 L / min / L reaction volume. During the reaction, the stirring speed is maintained at 350 rpm to keep the solid and liquid in suspension. The reaction temperature is kept constant at 80°C. The pH value of the system is precisely maintained at 7.8 by automatically adding 0.5 M sodium hydroxide solution or 0.5 M dilute hydrochloric acid solution. The change in conductivity is monitored in real time. When the rate of decrease in conductivity is less than 20% of the initial rate, the reaction is considered to be at its endpoint. The entire carbonization reaction lasts for 60 minutes.

[0046] S3: Aragonite-type calcium carbonate whiskers are generated through carbonation reaction. The aspect ratio of the aragonite whiskers is ≥10:1, and the heavy metal ions in the solid waste are embedded in the aragonite lattice through lattice substitution.

[0047] Preferably, the carbonization reaction is accompanied by stirring.

[0048] Furthermore, aragonite whiskers are the main crystalline phase of the carbonization products.

[0049] Specifically, the mass percentage of aragonite whiskers in the carbonized products is ≥60%.

[0050] Furthermore, the aspect ratio of aragonite whiskers is 10:1 to 30:1.

[0051] Specifically, after heavy metal ions are embedded in the aragonite lattice, their leaching concentration is reduced by more than 80%.

[0052] Furthermore, the average particle size of the carbonized products is 5~15μm.

[0053] Specifically, during the carbonization reaction, the process is monitored in real time by an online pH meter and conductivity meter, and the addition of alkaline or acidic solutions is automatically controlled.

[0054] Furthermore, after the carbonization reaction is completed, the product is subjected to solid-liquid separation, and the separated liquid is recycled as filtrate for step S1.

[0055] Specifically, solid-liquid separation is achieved using vacuum filtration or pressure filtration. The separated solid product does not require drying and can be directly used to prepare paste filling materials.

[0056] Preferably, the carbonization reaction produces a product with aragonite-type calcium carbonate whiskers as the main phase (mass percentage ≥60%, aspect ratio 10:1~30:1). These whiskers exert a micro-reinforcing effect in the paste—bridging microcracks, hindering crack propagation, and dissipating energy through pull-out effects—thereby significantly improving the flexural strength, fracture toughness, and crack resistance of the filler; simultaneously, heavy metal ions (Pb) 2+ Cd 2+ Cr 3+ As 3+ By embedding aragonite lattice through lattice substitution, a chemically bonded solid solution is formed, which reduces the leaching concentration of heavy metals by more than 80% and has a long-term stability far superior to traditional surface adsorption or physical encapsulation methods. The particle size of the carbonized product is refined to 5~15μm, which can fill the capillary pores of the paste. Moreover, the solid product after solid-liquid separation after the reaction can be used directly without drying, simplifying the process.

[0057] For example, after carbonization, a product with aragonite-type calcium carbonate whiskers as the main crystalline phase is generated. The whiskers account for more than 60% of the mass of the carbonized product, with an aspect ratio of 15:1 and an average particle size of about 10 μm. The lead and cadmium heavy metal ions in the solid waste are embedded in the aragonite lattice through lattice substitution, and their leaching concentration is reduced by more than 85%. After the reaction is completed, solid-liquid separation is carried out by vacuum filtration. The separated filtrate is reused for the preparation of the solid-liquid mixing system in step S1. The separated solid product does not need to be dried and is directly retained in its original state.

[0058] S4: The carbonized product containing aragonite whiskers obtained is used to prepare paste filling material.

[0059] Preferably, the carbonized products are used to replace part of the cement in the preparation of paste filling materials.

[0060] Specifically, the mass ratio of carbonation products replacing cement is 10% to 40%.

[0061] Furthermore, the paste filling material also contains coal gangue, fly ash, cement and water, with a mass concentration of 75% to 80%.

[0062] Specifically, the 28-day compressive strength of the paste filling material is ≥3.0MPa, which meets the strength requirements for paste filling in coal mines.

[0063] Preferably, the carbonization products containing aragonite whiskers directly replace part of the cement (10%~40%) in the preparation of paste filling materials, which can significantly reduce the amount of cement used and the high energy consumption and high carbon emissions caused by its production. At the same time, by utilizing the reinforcing effect of aragonite whiskers and the filling effect of carbonization products, the compressive strength of the paste can still reach more than 3.0 MPa after 28 days, meeting the strength standards for coal mine paste filling. In addition, this scheme achieves multiple goals of "CO2 mineralization and storage + safe resource utilization of heavy metal-containing solid waste + improvement of mechanical properties of filling body", providing an integrated technical path with low carbon, low cost and high environmental compatibility for green mine construction.

[0064] For example, the carbonized aragonite whisker product in S3, which does not require drying, is used to replace cement at a mass ratio of 25% and mixed with coal gangue, fly ash, remaining cement, and water to prepare a paste filling material with a mass concentration of 78%. The 28-day compressive strength of this paste filling material reaches 3.5 MPa, which meets the strength requirements for paste filling in coal mines. This not only reduces production energy consumption and carbon emissions by replacing cement, but also achieves multiple goals such as safe resource utilization of heavy metal solid waste, CO2 mineralization and storage, and improvement of the mechanical properties of the filling body.

[0065] In summary, this invention achieves multiple beneficial effects by mixing calcium-rich solid waste containing heavy metals with a magnesium source and introducing CO2 at 60-95℃ and pH 7.0-8.5 to generate a carbonization product with aragonite-type calcium carbonate whiskers as the main phase (length-to-diameter ratio ≥10:1). Simultaneously, heavy metal ions are inserted into the aragonite lattice through lattice substitution, resulting in: the micro-reinforcing effect of the aragonite whiskers significantly improves the flexural strength, toughness, and crack resistance of the paste filling material; the chemical bonding-level solidification of heavy metals greatly reduces the leaching risk, meeting environmental standards; the carbonization product can replace cement at a high proportion (≥40%), reducing filling costs and carbon emissions; and the process conditions are precisely controllable, with good compatibility with existing filling production lines. This broadens the safe resource utilization pathways for calcium-rich solid waste containing heavy metals and provides an integrated technical solution for green and low-carbon paste filling.

[0066] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for carbonization pretreatment of calcium-rich solid waste used for paste filling, characterized in that: include: The calcium-rich solid waste containing heavy metals is mixed with a magnesium source and formulated into a solid-liquid mixture system. A gas containing CO2 is introduced into the solid-liquid mixture, and a carbonization reaction is carried out at a temperature of 60~95℃, while maintaining a pH value of 7.0~8.5 during the reaction. Aragonite-type calcium carbonate whiskers are generated through a carbonation reaction. The aspect ratio of the aragonite-type whiskers is ≥10:1, and heavy metal ions in the solid waste are embedded in the aragonite lattice through lattice substitution. The carbonized product containing aragonite whiskers was used to prepare paste filling material.

2. The method for carbonization pretreatment of calcium-rich solid waste for paste filling as described in claim 1, characterized in that: The calcium-rich solid waste is at least one of carbide slag, steel slag, incineration fly ash, or calcium silicate slag.

3. The method for carbonization pretreatment of calcium-rich solid waste for paste filling as described in claim 1, characterized in that: The magnesium source is at least one of magnesium chloride, magnesium sulfate, or magnesium oxide; the magnesium source is premixed with calcium-rich solid waste using a dry method before solid-liquid mixing.

4. The method for carbonization pretreatment of calcium-rich solid waste for paste filling as described in claim 1, characterized in that: The liquid in the solid-liquid mixture is water or recycled filtrate; a crystal form regulator is added to the solid-liquid mixture, and the crystal form regulator is at least one of sodium citrate, sodium tartrate, or disodium ethylenediaminetetraacetate.

5. The method for carbonization pretreatment of calcium-rich solid waste for paste filling as described in claim 1, characterized in that: The carbonization reaction is accompanied by stirring.

6. The method for carbonization pretreatment of calcium-rich solid waste for paste filling as described in claim 1, characterized in that: The introduced CO2 gas is industrial exhaust gas or high-purity CO2; the CO2 is introduced in the form of microbubbles through a gas distributor.

7. The method for carbonization pretreatment of calcium-rich solid waste for paste filling as described in claim 1, characterized in that: During the reaction, the pH value is maintained at 7.0~8.5 by automatically adding alkaline or acidic solutions; the change in conductivity of the reaction system is monitored to determine the endpoint of the carbonization reaction.

8. The method for carbonization pretreatment of calcium-rich solid waste for paste filling as described in claim 1, characterized in that: The aragonite whiskers are the main crystalline phase of the carbonization product.

9. The method for carbonization pretreatment of calcium-rich solid waste for paste filling as described in claim 1, characterized in that: The heavy metals include at least one of lead, cadmium, chromium, and arsenic.

10. The method for carbonization pretreatment of calcium-rich solid waste for paste filling as described in claim 1, characterized in that: The carbonization products are used to replace part of the cement in the preparation of paste filling materials.

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