Metallic mine tailings-based carbon sequestration filling material, slurry preparation method and application

Abstract

This invention relates to the field of carbon sequestration technology, providing a carbon sequestration backfill material based on metal mine tailings, a slurry preparation method, and its application. Addressing the dual needs of metal mine tailings disposal and carbon sequestration, this invention offers a backfilling technology that utilizes the naturally strong alkalinity of metal mine tailings and cement hydration to achieve efficient carbon sequestration. Through a "gradient stirring + porous aeration" process, the gas-slurry contact efficiency is optimized, allowing carbon dioxide to fully react with calcium and magnesium ions in the tailings-cement system to generate carbonate precipitates. This permanently sequesters carbon dioxide and uses the precipitates to fill the gaps between particles, increasing the strength of the backfill. This simultaneously achieves the goals of tailings disposal, carbon sequestration, and goaf remediation, without requiring additional alkali activators, significantly reducing technical costs.

Description

Technical Field

[0001] This invention relates to the field of carbon fixation technology, specifically to a metal mine tailings-based carbon fixation backfill material, slurry preparation method, and application. Background Technology

[0002] Tailings generated during metal mining and beneficiation not only occupy arable land resources but also easily trigger ecological disasters such as landslides and heavy metal leakage. Currently, the mainstream disposal method for this type of tailings is cemented backfilling, which involves mixing tailings with cementitious materials such as cement and water to form a slurry, which is then backfilled into the mined-out area to ensure mine safety. However, this technology only achieves the "physical disposal" of tailings without exploring their environmental value, and it also has the problems of large cement consumption and high backfilling costs.

[0003] Current carbon sequestration and backfilling technologies are mostly concentrated in the coal mining sector. Coal mine tailings are mainly composed of clay, and their alkalinity is easily neutralized by acidic mine water after cement hydration (pH drops below 9), requiring the addition of alkaline activators to maintain carbon sequestration conditions. However, metal mine tailings are mainly composed of quartz and feldspar, which have high chemical stability. This fundamental difference between coal mine tailings and metal mine tailings means that coal mine carbon sequestration technologies cannot be transferred to metal mine tailings carbon sequestration and backfilling technologies. Carbon sequestration and backfilling technologies in the metal mining sector are currently in their infancy. Summary of the Invention

[0004] Therefore, it is necessary to provide a metal mine tailings-based carbon sequestration backfill material, a slurry preparation method, and its application. Without compromising slurry flowability or increasing alkali agent costs, the innovative combination of the metal mine tailings-based carbon sequestration backfill material and its prepared slurry in this invention can improve carbon sequestration efficiency and backfill strength, providing support for the industrial application of metal mine carbon sequestration backfill.

[0005] The present invention adopts the following technical solution: This invention provides a metal mine tailings-based carbon sequestration backfill material, comprising metal mine tailings, cementing material, water, and carbon dioxide; wherein the metal mine tailings contain 50-60 wt% quartz, 15-25 wt% feldspar, and a total content of ≥5 wt% CaO and MgO; the cementing material contains at least 50 wt% silicate cement, and the weight ratio of metal mine tailings to cementing material and carbon dioxide is 100:(10-20):(2-10).

[0006] In some embodiments, the metal ore tailings have a moisture content of ≤5%, a particle size range of 0.075~0.5mm, a total CaO and MgO content of ≥5%, and the main components are 50~60wt% quartz, 15~25wt% feldspar, and 5~10wt% calcium-magnesium minerals.

[0007] In some embodiments, the cementing material is selected from ordinary silicate cement.

[0008] In some embodiments, the cementitious material is selected from a mixture of ordinary Portland cement and slag powder, wherein the content of ordinary Portland cement is more than 50%, and the slag powder has a SiO2 content of ≥35wt%, an Al2O3 content of ≥10%, a CaO content of ≥35%, and a specific surface area of ​​≥400m² / g.

[0009] Preferably, the weight ratio of metal ore tailings to cementing material and carbon dioxide is 100:(10~20):(5~8).

[0010] The present invention also provides a method for preparing a carbon-fixing backfill slurry, comprising the following steps: obtaining the raw materials of the above-mentioned metal ore tailings-based carbon-fixing backfill material; mixing metal ore tailings, cementing materials, and water by stirring (preferably at 400~500 rpm) to obtain an alkaline slurry with a pH of 12.5~13.8; injecting carbon dioxide into the alkaline slurry through an array porous aeration process to obtain the carbon-fixing backfill slurry through a carbonization reaction.

[0011] In some embodiments, the parameters for injecting carbon dioxide are: stirring speed 200~300 rpm (to avoid bubble breakage), aeration orifice diameter 20~100 μm, aeration pressure 0.3~0.6 MPa, flow rate 0.8~1.2 L / min, and injection time 5~10 minutes.

[0012] In some embodiments, the ratio of metal tailings, cementitious material, and water is 100:(10~20):(28~45).

[0013] This invention also provides the application of the above-mentioned carbon-fixing backfill slurry in filling ore goaf areas. Preferably, the carbon-fixing backfill slurry is introduced into the goaf area and, through natural curing, forms a mine backfill body.

[0014] In particular, the carbon sequestration filling slurry, under conditions of a concentration of 60-70% and a lime-sand ratio of 1:5-1:12, has a 28-day compressive strength of ≥4.0MPa and a carbon sequestration rate of ≥1.0%, making it suitable for filling goaf areas in metal mines.

[0015] Compared with the prior art, the core technical advantages and beneficial effects of this invention are as follows: The core mechanism of the carbon sequestration filling technology of this invention is "natural strong alkalinity driving + gas-slurry optimized reaction + solid waste synergistic enhancement": 1) Ordinary silicate cement and metal mine tailings hydrate to generate a large amount of Ca(OH)2, so that the slurry naturally forms a strong alkaline environment with a pH of 12.5~13.8. This environment can increase the carbon dioxide dissolution rate by more than 10 times and rapidly generate HCO3. - CO3 2-1) Plasma; 2) Through array-type aeration and gradient stirring optimization, the diameter of carbon dioxide bubbles is stabilized at 50~100μm, which fully contacts the calcium and magnesium ions (released by cement hydration + contained in the tailings) on the surface of tailings particles to generate nano-sized calcium carbonate precipitate; 3) The calcium carbonate precipitate fills the pores between tailings and cement hydration products (CSH gel) to form a "CSH gel + carbonate" double cementing structure, which not only achieves permanent carbon dioxide sequestration, but also significantly improves the density and strength of the filling body.

[0016] The present invention addresses the following technical challenges in the preparation of metal mine tailings-based carbon sequestration filling materials and slurries: 1) It designs an air-slurry mixing process tailings with fine-grained characteristics to solve the problems of easy carbon dioxide bubble escape and low carbon sequestration efficiency; 2) It balances the carbon sequestration reaction and slurry fluidity to solve the technical problem that carbonization products can easily lead to rapid slurry solidification and affect downhole transportation; 3) It provides a "carbon sequestration-strength" synergistic control method to ensure carbon sequestration while improving the performance advantages of the filling body.

[0017] This invention relates to a carbon sequestration backfill material that uses tailings from metal ore beneficiation as the main aggregate, combined with ordinary silicate cement to construct a naturally alkaline backfill system (the slurry pH reaches 12.5-13.8 after cement hydration). During the tailings slurry preparation process, carbon dioxide gas is precisely introduced, utilizing the system's inherent alkaline environment to accelerate the carbonization reaction between carbon dioxide and calcium and magnesium ions. Simultaneously, the carbon-containing tailings slurry is filled into the mine's goaf, ultimately achieving the triple objectives of "tailings disposal + carbon sequestration + goaf stability control." This invention addresses the problems of the lack of carbon emission reduction value in traditional tailings backfilling and the high cost of carbon dioxide geological sequestration, providing the mining industry with a low-cost, highly adaptable technical path, especially suitable for mines with large tailings emissions, such as non-ferrous and ferrous metal mines.

[0018] Carbon dioxide capture and storage (CCUS) is a key technology for achieving the "dual carbon" target, but existing geological methods (such as depleted oil and gas fields and saline aquifers) suffer from drawbacks such as stringent site selection, high engineering costs, and difficulties in monitoring, hindering large-scale implementation. Research has confirmed that in the cemented backfilling of metal mine tailings, the pH value of the pore solution after hydration with ordinary silicate cement can reach 12.5–13.8, creating a naturally strong alkaline environment—ideal conditions for the efficient carbonization of carbon dioxide with calcium and magnesium ions to form stable carbonate precipitates. However, current metal mine tailings backfilling technology only utilizes cement hydration for strength support, completely failing to explore its strong alkaline carbon sequestration value. This leads to a contradiction between "wasting natural carbon sequestration conditions" and "the urgent need for carbon emission reduction." Therefore, combining tailings backfilling with carbon sequestration through process optimization is the core breakthrough for green development in mining.

[0019] This invention utilizes a double-bonded structure formed by carbonate precipitation and CSH gel, resulting in a 39-50% increase in 28-day compressive strength compared to traditional filling techniques, reduced porosity, and superior long-term stability. It eliminates the need for new carbon sequestration sites, leveraging existing mine filling systems to achieve carbon sequestration, thus reducing filling material costs by 15-20%. Carbon oxide is permanently stored underground in the form of carbonate minerals, eliminating leakage risks and meeting the requirements of the "Carbon Sequestration Technology Standard" (GB / T 41010-2021), demonstrating high carbon sequestration stability. Attached Figure Description

[0020] Figure 1 A schematic diagram illustrating the preparation method and application of carbon sequestration backfill materials and slurries for metal mine tailings.

[0021] Figure 2 A detailed flowchart illustrating the preparation methods and application processes of carbon sequestration filling materials and slurries for metal mine tailings. Detailed Implementation

[0022] like Figure 1 As shown, the technical concept of this invention is to provide a flowchart of a metal mine tailings-based carbon-fixing backfill material, a slurry preparation method, and the application of the backfill. By drying and pretreating the metal mine tailings, a carbon-fixing slurry is prepared by coordinating a specific ratio of cementitious materials, water, and carbon dioxide to undergo a carbonization reaction. This slurry is then input into the well to form a backfill, ensuring high strength and high carbon fixation rate of the backfill after standard curing.

[0023] The present invention will be further described in detail below with reference to specific embodiments, so that those skilled in the art can more clearly understand the present invention. The following embodiments are only used to illustrate the present invention, and are not intended to limit the scope of the present invention. Based on the specific embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention. In the embodiments of the present invention, unless otherwise specified, all raw material components are commercially available products well known to those skilled in the art; in the embodiments of the present invention, unless specifically specified, the technical means used are conventional means well known to those skilled in the art.

[0024] Key ingredient descriptions: Metal ore tailings: derived from non-ferrous metal ore beneficiation, with a moisture content of ≤5% and a particle size of 0.075~0.5mm. The main components are quartz 55%, feldspar 22%, and calcium-magnesium minerals 5.6% (CaO 3.5%, MgO 2.1%). It provides a reaction carrier and aggregate support for carbon sequestration. Before use, it is dried and pretreated (sent to an 80℃ forced-air oven for 6 hours until the moisture content is ≤5%).

[0025] Slag powder: sourced from steel plants, main components: SiO2 content 38wt%, Al2O3 content 15wt%, CaO content 40wt%, physicochemical indicators: specific surface area ≥400m² / g, activity index ≥95% (7 days).

[0026] Coal mine tailings: originating from coal mines, main components: 50% clay content, 30wt% quartz content, 15wt% feldspar content, physicochemical indicators: 8% moisture content, pH 7.2.

[0027] Carbon dioxide: Liquid carbon dioxide (purity ≥99.5%) is vaporized or supercritically treated and then introduced into the slurry to provide raw materials for carbon sequestration.

[0028] The following example illustrates this.

[0029] Example 1 This embodiment provides a metal mine tailings-based carbon fixation backfill material, comprising the following raw materials in parts by weight: 100 parts metal mine tailings, 15 parts ordinary silicate cement (P·O 42.5, cementing material), 35 parts water, and 2 parts carbon dioxide.

[0030] This embodiment also provides a method for preparing and filling carbon fixation slurry, including the following steps: S1, Preparation of alkaline slurry: According to the above raw material ratio, put the metal ore tailings, ordinary Portland cement (P·O 42.5) and water into a twin-shaft mixing tank and stir at 450 rpm for 3 minutes to form a uniform slurry.

[0031] S2, carbonization reaction: Reduce the stirring speed to 250 rpm (to avoid bubble breakage), and introduce carbon dioxide into the slurry through an array of porous aeration discs (pore size 50μm). Control the gas pressure to 0.4~0.5MPa, the flow rate to 1.0L / min, and the introduction time to 10 minutes to obtain the filling slurry.

[0032] S3, Maintenance: Place the filling grout in the well and allow it to cure naturally: ambient temperature 15~30℃, humidity ≥85%, for 28 days.

[0033] Example 2 This embodiment provides a metal mine tailings-based carbon fixation backfill material, comprising the following raw materials in parts by weight: 100 parts metal mine tailings, 15 parts ordinary silicate cement (P·O 42.5, cementing material), 35 parts water, and 5 parts carbon dioxide.

[0034] The carbon fixation filling method in this embodiment is basically the same as that in Embodiment 1.

[0035] Example 3 This embodiment provides a metal mine tailings-based carbon fixation backfill material, comprising the following raw materials in parts by weight: 100 parts metal mine tailings, 15 parts ordinary silicate cement (P·O 42.5, cementing material), 35 parts water, and 8 parts carbon dioxide.

[0036] The preparation and filling methods of the carbon fixation slurry in this embodiment are basically the same as those in Example 1.

[0037] Example 4 This embodiment provides a metal mine tailings-based carbon fixation backfill material, comprising the following raw materials in parts by weight: 100 parts metal mine tailings, 15 parts ordinary silicate cement (P·O 42.5, cementing material), 35 parts water, and 10 parts carbon dioxide.

[0038] The preparation and filling methods of the carbon fixation slurry in this embodiment are basically the same as those in Example 1.

[0039] Comparative Example 1 This comparative example provides a metal mine tailings-based carbon sequestration backfill material, comprising the following raw materials in parts by weight: 100 parts metal mine tailings, 15 parts ordinary silicate cement (P·O 42.5, cementing material), 35 parts water, and no carbon dioxide.

[0040] The comparative slurry preparation and filling method includes the following steps: S1, Preparation of alkaline slurry: According to the above raw material ratio, put the metal ore tailings, ordinary Portland cement (P·O 42.5) and water into a twin-shaft mixing tank and stir at 450 rpm for 3 minutes to form a uniform slurry.

[0041] S2, Maintenance: The slurry prepared in step S1 is placed in the well for natural curing at an ambient temperature of 15~30℃ and humidity ≥85% for 28 days.

[0042] Comparative Example 2 This comparative example provides a coal mine tailings carbon sequestration backfilling technology. The carbon sequestration backfilling material contains the following raw materials in parts by weight: 100 parts coal mine tailings, 15 parts ordinary silicate cement (P·O 42.5, cementing material), 35 parts water, and 5 parts carbon dioxide.

[0043] The comparative method for preparing and filling carbon fixation slurry includes the following steps: S1, Preparation of alkaline slurry: According to the above raw material ratio, coal mine tailings, ordinary Portland cement (P·O 42.5), and water were added to a twin-shaft mixing tank and stirred at 450 rpm for 3 minutes to form a uniform slurry. Testing showed that the pH value of the slurry pore solution was 12.0.

[0044] S2, carbonization reaction: Reduce the stirring speed to 250 rpm (to avoid bubble breakage), and introduce carbon dioxide into the slurry through an array of porous aeration discs (pore size 50 μm). Control the gas pressure to 0.4~0.5 MPa, the flow rate to 1.0 L / min, and the introduction time to 10 minutes to obtain the filling slurry.

[0045] S3, Maintenance: The filling slurry is placed underground for natural curing at an ambient temperature of 15~30℃ and humidity ≥85% for 28 days.

[0046] The fluidity, initial pH value before carbonization, pH value after carbonization, filling and curing effects (compressive strength at 3 days, 7 days and 28 days), and carbon sequestration rate of the slurry prepared in the above test examples were monitored respectively.

[0047] The statistical results are shown in the table below: Statistical table of slurry curing effect and carbon fixation effect As can be seen from the table above: As can be seen from Comparative Example 1 and Examples 1 to 4, under essentially the same test conditions (ash-sand ratio 1:6.7, slurry concentration 65%, density 1.70 t / m³, mix ratio of 100 parts tailings, 15 parts cement, and 35 parts water), the introduction of carbon dioxide can improve the curing strength of the metal ore tailings slurry and achieve a good carbon fixation effect.

[0048] Compared with Comparative Example 2 (traditional coal mine tailings), the solidification strength of using metal mine tailings slurry as filling material is significantly improved, and the carbon sequestration rate is doubled or more.

[0049] Example 5 Referring to the process steps of Example 3, this example explores the influence of the composition of the cementitious material (different content ratios of ordinary silicate cement and slag powder) on the prepared carbon-fixing slurry and filling effect.

[0050] The statistical results are shown in the table below: Statistical table of slurry curing effect and carbon fixation effect like Figure 2 As shown, and not limited to the above experimental examples, the inventors' team discovered through extensive experimentation that: (1) Preferred carbon fixation backfill material based on metal mine tailings: 100 parts of metal mine tailings, 10-20 parts of ordinary silicate cement (P·O42.5, cementing material), 28-45 parts of water, and 2-10 parts of carbon dioxide.

[0051] (2) Optimization of process conditions for slurry preparation and carbonization reaction: The slurry is formed by biaxial stirring at 400~500 rpm for 3~5 minutes to form a strong alkaline slurry (pH 12.5~13.8). Then, carbon dioxide is introduced through an array of porous aeration discs while maintaining a low stirring speed (200~300 rpm) to complete carbon fixation and obtain a carbon fixation slurry with pH reduced to 10.0~11.5.

[0052] (3) Fill the goaf with carbon sequestration slurry and cure it naturally: temperature 15~30℃, humidity not less than 85%, oxidation for 3~28 days to obtain a filling body with a strength greater than 4.0MPa and a carbon sequestration rate greater than 2% after 28 days.

[0053] Specifically, the technological advantages are reflected in the following aspects: (1) This invention utilizes ordinary silicate cement and metal mine tailings in a specific ratio to create a naturally formed strong alkaline environment (pH 12.5~13.8) through hydration. By optimizing the gas-slurry contact efficiency through a "gradient stirring + porous aeration" process, carbon dioxide reacts fully with calcium and magnesium ions in the metal mine tailings-cement system to generate carbonate precipitates. This not only permanently seals carbon dioxide but also uses the precipitates to fill the gaps between particles and improve the strength of the backfill. This simultaneously achieves the goals of tailings disposal, carbon sequestration, and goaf treatment, without the need for additional alkali activators, thus significantly reducing technical costs.

[0054] (2) The carbon fixation filling technology of this invention mainly uses ordinary silicate cement (P·O 42.5 and above), and can be compounded with up to 50% slag powder (specific surface area ≥400m² / kg) to achieve the core function: hydration generates Ca(OH)2 to form a strongly alkaline environment with pH 12.5~13.8, while releasing a large amount of calcium and magnesium ions, providing core reactants for the carbonization reaction. It is easy to adjust the filling slurry concentration to 60~70%, ensuring that the slurry fluidity is ≥255mm, which meets the requirements of downhole transportation.

[0055] (3) This invention can use liquid carbon dioxide (purity ≥99.5%), which is vaporized or supercritically treated and then introduced into the slurry to provide raw materials for carbon sequestration. Preferably, the stirring speed is reduced to 200~300 rpm (to avoid bubble breakage), and carbon dioxide is introduced into the slurry through an array of porous aeration discs (pore size 50μm). The gas pressure is controlled at 0.3~0.6 MPa, the flow rate at 0.8~1.2 L / min, and the introduction time at 5~10 minutes to achieve the advantages of carbon dioxide injection into the carbon sequestration slurry. Through optimization of the gas-slurry mixing process: a gradient stirring of "high speed first and then low speed" is combined with array of microporous aeration. 50~100μm CO2 microbubbles are introduced under low-speed stirring, which greatly prolongs the gas-liquid-solid three-phase contact time and improves the carbon sequestration efficiency. By controlling the amount of CO2, the generated nano-sized calcium carbonate precipitate effectively fills the particle pores and forms a double cementing structure with the cement hydration products (CSH gel), synergistically achieving a technological breakthrough in high strength and high carbon sequestration rate.

[0056] It should be noted that the above embodiments are only for further elaboration and explanation of the technical solution of the present invention, and are not intended to further limit the technical solution of the present invention. The method of the present invention is only a preferred embodiment and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A carbon fixation and backfilling material based on metal ore tailings, characterized in that, It contains metal ore tailings, cementing materials, water, and carbon dioxide; Among them, the tailings of metal mines contain 50-60 wt% quartz, 15-25 wt% feldspar, and a total content of ≥5 wt% CaO and MgO; The cementitious material contains at least 50 wt% silicate cement; The weight ratio of metal ore tailings to cementing materials and carbon dioxide is 100:(10~20):(2~10).

2. The metal ore tailings-based carbon sequestration backfill material according to claim 1 or 2, characterized in that, The metal ore tailings have a moisture content of ≤5% and a particle size range of 0.075~0.5mm.

3. The metal ore tailings-based carbon sequestration backfill material according to claim 1 or 2, characterized in that, The cementitious material is selected from ordinary Portland cement; or The cementitious material is selected from a mixture of ordinary Portland cement and slag powder, with the ordinary Portland cement content accounting for more than 50%, and the slag powder having a SiO2 content ≥35wt%, an Al2O3 content ≥10%, a CaO content ≥35%, and a specific surface area ≥400m² / g.

4. The metal ore tailings-based carbon sequestration backfill material according to claim 1 or 2, characterized in that, The weight ratio of metal ore tailings to cementing materials and carbon dioxide is 100:(10~20):(5~8).

5. A method for preparing a carbon-fixing filling slurry, characterized in that, Includes the following steps: Obtain the raw materials for the metal mine tailings-based carbon sequestration backfill material according to any one of claims 1 to 4; Metal ore tailings, cementitious materials, and water are mixed to prepare an alkaline slurry with a pH of 12.5 to 13.

8. Carbon dioxide is injected into alkaline slurry through an array porous aeration process, and carbonization reaction is carried out to obtain carbon-fixed filling slurry.

6. The method for preparing the carbon-fixing filling slurry according to claim 5, characterized in that, The parameters for injecting carbon dioxide are as follows: stirring speed 200~300 rpm, aeration pore size 20~100μm, aeration pressure 0.3~0.6 MPa, flow rate 0.8~1.2 L / min, and injection time 5~10 minutes.

7. The method for preparing the carbon-fixing filling slurry according to claim 5, characterized in that, Metal ore tailings, cementitious materials, and water: 100: (10~20): (28~45).

8. The method for preparing the carbon-fixing filling slurry according to claim 5, characterized in that, The stirring speed during the preparation of the alkaline slurry is 400-500 rpm.

9. The application of the carbon-fixing backfill slurry prepared according to any one of claims 5 to 8 in backfilling ore goaf areas.

10. The application according to claim 9, characterized in that, The carbon-fixing filling slurry prepared according to any one of claims 5 to 8 is input into the goaf and, through natural curing, forms a mine backfill body.

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