All-solid waste coal gangue based geopolymer backfill material as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of building materials, and particularly relates to an all-solid waste coal gangue based geopolymer backfill material as well as a preparation method and application thereof. The invention provides a novel cementing material which can fully utilize a large amount of industrial solid waste, an activator is also mainly from industrial waste, the preparation process is simple, and the novel cementing material is used for replacing cement to be used for mine backfill. The coal gangue powder and the mineral powder are used as main silicon-aluminum active substances, and the carbide slag and the red mud are used as alkali activators; a small amount of sodium hydroxide is used as an additional alkali source, and the all-solid waste coal gangue based geopolymer with good construction performance and mechanical performance is prepared through simple mixing. The compressive strength of the prepared geopolymer backfill material exceeds 8 MPa after the geopolymer backfill material is coagulated and hardened for 28 days, the performance requirements of the geopolymer backfill material are met and remarkably superior to those of a mine backfill material, the utilization value of industrial solid waste is greatly improved, and the geopolymer backfill material has good environmental protection benefits and application prospects.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology, specifically relating to a solid waste coal gangue base polymer backfill material and its preparation method and application. Coal gangue powder and slag powder are used as silica-alumina precursors, carbide slag and red mud are used as alkali activators, and a small amount of sodium hydroxide is added as an external alkali source to prepare a solid waste geopolymer cementitious material that can be used for mine backfilling. Background Technology

[0002] With the advancement of global "dual carbon" goals, the cement industry, as a core sector with high carbon emissions, must inevitably undergo emission reduction and transformation. Data shows that producing one ton of traditional cement clinker emits approximately 900-1000 kg of carbon dioxide, with about 60% of these emissions originating from the unavoidable high-temperature decomposition of limestone. This makes it difficult for the traditional cement industry to achieve substantial emission reductions through conventional energy-saving methods.

[0003] Among numerous cement alternatives, geopolymers have emerged as one of the most promising mainstream routes due to their significant carbon reduction advantages and resource recycling characteristics. Geopolymers are generated through alkali-activated aluminosilicate waste materials. The production process does not require calcining limestone, resulting in carbon emissions that are only 20%-30% of traditional silicate cement, achieving a carbon reduction rate of 70%-90%. EPA and IPCC data show that ordinary silicate cement concrete emits approximately 777 kg of carbon per ton, while geopolymer concrete emits only about 215 kg, demonstrating a significant emission reduction effect. More importantly, geopolymers can utilize 100% industrial solid waste as raw materials. Large quantities of solid waste such as fly ash, slag, steel slag, and red mud can be transformed into high-performance cementitious materials, perfectly aligning with the "waste-to-waste" concept. In contrast, traditional cement-based materials are limited by hydration mechanisms, typically incorporating no more than 30%-50% solid waste, and requiring high-quality waste. For low-quality solid waste, the dosage is often less than 20%, making it difficult to meet the needs of large-scale resource utilization.

[0004] Mine backfilling is a key technology for ensuring safe mine production and controlling surface subsidence, and it has been widely applied in scenarios such as coal mining under "three-under" conditions (buildings, railways, and water bodies) and goaf remediation. Currently, the application rate of cemented backfilling mining technology in my country exceeds 60%, but the cementing material used is still mainly ordinary Portland cement. Although cement-based backfilling materials can basically meet the mechanical strength requirements of the backfill, their inherent defects such as high carbon emissions and low solid waste utilization rate are no longer suitable for the needs of low-carbon development and resource recycling. Against this backdrop, exploring the use of geopolymers, which have significant carbon reduction potential and strong solid waste applicability, to replace cement for coal mine backfilling has become a feasible way to solve industry pain points and promote the green transformation of mines.

[0005] In summary, there is an urgent need to provide a novel cementitious material that can fully utilize large quantities of industrial solid waste, whose activators are also mainly derived from industrial waste, and whose preparation process is simple, to replace cement for mine backfilling. This material should possess suitable setting time, sufficient early strength, and excellent later-stage mechanical properties, while meeting the fluidity and durability requirements of mine backfilling construction, thereby achieving more efficient utilization of solid waste resources and low-carbon mining practices. Summary of the Invention

[0006] This invention addresses the aforementioned problems by providing a solid waste coal gangue-based geopolymer backfill material, its preparation method, and its application. The invention uses coal gangue powder and slag powder as the main active silica-alumina raw materials, employs carbide slag and red mud as alkaline activators, and adds a small amount of sodium hydroxide as an external alkali source to compensate for the insufficient early-stage reactivity of the pure solid waste activator. This results in a solid waste geopolymer cementitious material with high early-stage strength and good later-stage mechanical properties, which can be used for backfilling of mine goaf areas.

[0007] To achieve the above objectives, the present invention employs the following technical solution:

[0008] In a first aspect, the present invention provides a polymer backfill material for solid waste coal gangue bases, which is composed of the following raw materials in parts by weight:

[0009] 30-45 parts coal gangue powder, 15-30 parts mineral powder, 40 parts calcium carbide slag or 40 parts red mud, 5 parts sodium hydroxide, and 62 parts water.

[0010] Furthermore, the coal gangue powder is a fine powder made from coal gangue after high-temperature calcination. Its chemical composition contains ≥95% SiO2 and Al2O3, ≤0.2% CaO, and a median particle size Dv(50) of 4.5-4.7μm. The calcined coal gangue is activated to improve the reactivity of SiO2 and Al2O3 (% is mass percentage).

[0011] The mineral powder is slag powder (also known as slag powder) obtained by grinding granulated blast furnace slag. Its chemical composition has a CaO content of 37-39% and a Dv(50) of 6.4-6.7μm. It has potential hydraulic activity and can participate in the reaction to generate hydration products under alkaline conditions (% is mass percentage).

[0012] The calcium carbide slag is an industrial byproduct of calcium carbide (hydrolysis to produce acetylene gas), with calcium hydroxide as its main component and an effective alkali equivalent of 78-80% and a specific surface area of ​​2800-2900 m². 2 / kg, used as one of the alkaline activators in this invention (% is by mass percentage).

[0013] The red mud is an alkaline tailings from alumina production, with an Al2O3 content of 20-30% and an effective alkali equivalent of 12-15%, and a specific surface area of ​​2800-3000 m². 2 / kg, which is used as another alkaline activator in this invention (% is by mass percentage).

[0014] Sodium hydroxide is industrial soda ash (NaOH). In this invention, only a small amount (approximately 3%–5% of the total solids) is added as an external activator to provide additional OH- in the initial reaction stage. - To increase the pH of the system and accelerate the dissolution and reaction of the silicon-aluminum raw materials. All of the above raw materials are industrial by-products or wastes (except sodium hydroxide), among which coal gangue, slag, carbide slag, and red mud are widely available and inexpensive (% is by mass percentage).

[0015] Secondly, the present invention provides a method for preparing a polymer backfill material for solid waste coal gangue base, comprising the following steps:

[0016] Step 1: Mix calcined coal gangue powder, mineral powder, carbide slag or red mud, and sodium hydroxide in proportion, add water and continue stirring until a uniform slurry is formed.

[0017] Step 2: The mixed slurry is poured into shape and cured under moist conditions to obtain the solid waste coal gangue base polymer backfill material.

[0018] Furthermore, the curing conditions in step 2 are a temperature of 20±2℃ and a relative humidity of not less than 95%.

[0019] Thirdly, this invention provides an application of a polymer backfill material for solid waste coal gangue base in mine backfilling.

[0020] Furthermore, the solid waste coal gangue base polymer backfill material is used as a cemented filling material for mine goaf areas to replace cement-based cementitious materials for underground mine backfilling.

[0021] In practical applications, the geopolymer cementitious material prepared by this invention can be used as a binder for mine backfill slurry. It is stirred to form a backfill slurry, pumped to the goaf area, and hardened to form a backfill body. Because the cementitious material of this invention develops strength rapidly in its early stages, the backfill body can reach a compressive strength of several MPa within 1-3 days, basically meeting the initial support requirements for roadway backfilling. The compressive strength after 28 days can reach 4-8 MPa or more, fully meeting the long-term stability requirements of the mine.

[0022] Compared with the prior art, the present invention has the following advantages:

[0023] 1. This invention uses red mud or carbide slag as a solid waste alkaline activator to activate coal gangue and mineral powder. Red mud or carbide slag is rich in highly active components such as Na2O and Ca(OH)2. As an alkaline activator, it can construct a strongly alkaline system, efficiently activate the active Si and Al components in coal gangue and mineral powder, induce their depolymerization and repolymerization, generate a dense polymer cementitious phase, and endow the material with excellent mechanical properties.

[0024] 2. The cementitious material of this invention is mainly composed of industrial solid waste, including coal gangue powder, slag powder, carbide slag, and red mud. All cementing components are industrial by-products, with only a very small amount of sodium hydroxide added for auxiliary activation. This achieves nearly 100% solid waste resource utilization of the cementing material components, significantly reducing reliance on traditional cement clinker or commercial chemicals. This not only lowers material costs but also effectively disposes of large quantities of industrial waste, resulting in significant ecological and economic benefits.

[0025] 3. The geopolymer backfill material prepared by this invention exhibits high strength and good durability after hardening. Its 28-day compressive strength exceeds the current industry standard requirements for backfill material strength. The flexural strength of the material also reaches above 2.5-3.5 MPa, indicating that the backfill has good toughness and crack resistance. In addition, the geopolymer material has good durability and corrosion resistance; for example, its resistance to sulfate attack and alkali-aggregate reaction is superior to that of ordinary silicate cement materials, enabling it to maintain long-term stability in groundwater and corrosive mine water environments.

[0026] 4. The material of this invention produces a highly fluid slurry that is easy to pump and pour. The moderate setting and hardening time facilitates construction operations and process coordination, allowing the material sufficient working time to complete pumping and filling operations, and also allowing it to harden and solidify within a reasonable time after filling, without delaying subsequent mining progress.

[0027] 5. The preparation process of this invention is simple, requiring only the mixing of dry materials at room temperature and the addition of water to form a slurry, eliminating cumbersome chemical treatment and additional energy consumption, and facilitating direct mixing and use on-site in mining areas. Furthermore, since the main raw materials are all industrial waste, the raw material cost is extremely low, and the overall cost is significantly lower than that of ordinary cement and traditional geopolymer cementitious materials, enabling low-cost, large-scale promotion and application.

[0028] In summary, this invention has significant advantages in high-value utilization of solid waste, low-carbon environmental protection, and material performance. It provides a practical and feasible cement-based alternative to cementitious materials for the application scenario of coal mine backfilling, and has high value for promotion and application. Detailed Implementation

[0029] To further illustrate the technical solution of the present invention, the present invention will be further described below through embodiments.

[0030] Example 1

[0031] This embodiment of a solid waste coal gangue base polymer backfill material is composed of the following parts by weight of raw materials:

[0032] 30 parts coal gangue powder, 30 parts mineral powder, 40 parts red mud, 5 parts sodium hydroxide, and 62 parts water.

[0033] Among them, the coal gangue powder is the fine powder after high-temperature calcination of coal gangue. Its chemical composition contains SiO2 and Al2O3 total ≥95%, CaO ≤0.2%, and median particle size Dv(50) is 4.5-4.7μm.

[0034] The ore powder is slag micro powder (also known as slag powder) obtained by grinding granulated blast furnace slag. Its chemical composition has a CaO content of 37-39% and a Dv(50) of 6.4-6.7μm.

[0035] Calcium carbide slag is an industrial byproduct of calcium carbide (hydrolysis to produce acetylene gas). Its main component is calcium hydroxide, with an effective alkali equivalent of 78-80% and a specific surface area of ​​2800-2900 m². 2 / kg.

[0036] Red mud is an alkaline tailings from alumina production. Its chemical composition includes 20-30% Al₂O₃, an effective alkali equivalent of 12-15%, and a specific surface area of ​​2800-3000 m². 2 / kg.

[0037] Sodium hydroxide is industrial soda ash (NaOH).

[0038] The preparation method of the polymer backfill material for the solid waste coal gangue base includes the following steps:

[0039] Step 1: Place coal gangue powder, mineral powder, red mud, and sodium hydroxide into a cement mortar mixer and mix at low speed for 30 seconds to obtain mixture 1;

[0040] Step 2: Add water to mixture 1 from step 1 and continue stirring at low speed for 90 seconds to obtain mixture 2. Continue stirring at high speed for 60 seconds to form a uniform slurry. The rotation / revolution speeds in the low-speed stage are (140±5) r / min and (62±5) r / min, respectively, and the speeds in the high-speed stage are (285±10) r / min and (125±10) r / min, respectively.

[0041] Step 3: The mixed slurry is poured into shape and cured under humid conditions (temperature 20±2℃, relative humidity not less than 95%) to obtain the solid waste coal gangue base polymer backfill material.

[0042] Example 2

[0043] The difference from Example 1 is that: 35 parts coal gangue powder, 25 parts mineral powder, 40 parts red mud, 5 parts sodium hydroxide, and 62 parts water.

[0044] Example 3

[0045] The difference from Example 1 is that: 40 parts coal gangue powder, 20 parts mineral powder, 40 parts red mud, 5 parts sodium hydroxide, and 62 parts water.

[0046] Example 4

[0047] The difference from Example 1 is that: 45 parts coal gangue powder, 15 parts mineral powder, 40 parts red mud, 5 parts sodium hydroxide, and 62 parts water.

[0048] Example 5

[0049] The difference from Example 1 is that: 30 parts coal gangue powder, 30 parts mineral powder, 40 parts carbide slag, 5 parts sodium hydroxide, and 62 parts water.

[0050] Example 6

[0051] The difference from Example 1 is that: 35 parts coal gangue powder, 25 parts mineral powder, 40 parts carbide slag, 5 parts sodium hydroxide, and 62 parts water.

[0052] Example 7

[0053] The difference from Example 1 is that: 40 parts coal gangue powder, 20 parts mineral powder, 40 parts carbide slag, 5 parts sodium hydroxide, and 62 parts water.

[0054] Example 8

[0055] The difference from Example 1 is that: 45 parts coal gangue powder, 15 parts mineral powder, 40 parts carbide slag, 5 parts sodium hydroxide, and 62 parts water.

[0056] The flowability, setting time, 28-day compressive strength and 28-day flexural strength of the all-solid waste geopolymer backfill material prepared according to the above embodiments were tested, and the test results are shown in Table 1.

[0057] Table 1 Performance Test Results of Geopolymer Backfill Materials for All Solid Waste

[0058] Liquidity test Condensation time test Compressive strength test Flexural strength test Example 1 240 mm 99 min 12.70 MPa 3.16 MPa Example 2 239 mm 117 min 11.83 MPa 2.51 MPa Example 3 270 mm 212 min 11.09 MPa 2.68 MPa Example 4 271 mm 189 min 8.43 MPa 2.44 MPa Example 5 245 mm 52 min 5.61 MPa 4.72 MPa Example 6 237 mm 114 min 5.24 MPa 3.82 MPa Example 7 266 mm 70 min 5.33 MPa 4.63 MPa Example 8 239 mm 130 min 6.32 MPa 4.29 MPa

[0059] The test results above show that the all-solid waste geopolymer backfill material prepared by this invention has a 28-day compressive strength greater than 4.5 MPa, which fully meets the strength requirements for mine backfilling. The geopolymer backfill material prepared by this invention can be used as a cemented filling material for mine goaf areas to replace cement-based cementitious materials for underground mine backfilling.

[0060] Comparing Examples 1-4 and Examples 5-8 reveals that using red mud as an activator yields superior later-stage performance, while using calcium carbide slag as an activator results in better early-stage performance. The method for preparing the all-solid-waste geopolymer backfill material of this invention not only achieves large-scale utilization of industrial solid waste and solves the hidden dangers posed by industrial solid waste, but also addresses the problem of consuming large amounts of cement for mine backfilling, thereby reducing carbon emissions and economic energy consumption.

[0061] In summary, this invention provides a geopolymer cementitious material based on solid wastes such as coal gangue, slag, carbide slag, and red mud, along with its preparation and application methods. Through rational design of the component ratios and activation system, the material exhibits comprehensive advantages such as high fluidity, rapid setting, high strength, and high solid waste utilization rate. It can effectively replace cement in mine backfilling, achieving large-scale disposal of mining solid waste and low-carbon mine backfilling, thus providing a new technical approach for safe mining and environmental protection.

[0062] The foregoing has shown and described the main features and advantages of the present invention. It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

[0063] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A polymer backfill material for solid waste coal gangue bases, characterized in that, Composed of the following raw materials in parts by weight: 30-45 parts coal gangue powder, 15-30 parts mineral powder, 40 parts calcium carbide slag or 40 parts red mud, 5 parts sodium hydroxide, and 62 parts water.

2. The polymer backfill material for solid waste coal gangue base as described in claim 1, characterized in that, The coal gangue powder is a fine powder obtained by high-temperature calcination of coal gangue, with a total SiO2 and Al2O3 content of ≥95%, CaO ≤0.2%, and a median particle size of 4.5-4.7μm. The mineral powder has a CaO content of 37-39% and a median particle size of 6.4-6.7 μm. The carbide slag has a Ca(OH)₂ content of 78-80%, an effective alkali equivalent of 78-80%, and a specific surface area of ​​2800-2900 m². 2 / kg; The red mud has an Al2O3 content of 20-30%, an effective alkali equivalent of 12-15%, and a specific surface area of ​​2800-3000 m². 2 / kg, where all percentages are by mass.

3. The method for preparing a polymer backfill material for solid waste coal gangue base as described in claim 2, characterized in that, Includes the following steps: Step 1: Mix calcined coal gangue powder, mineral powder, carbide slag or red mud, and sodium hydroxide in proportion, add water and continue stirring until a uniform slurry is formed. Step 2: The mixed slurry is poured into shape and cured under moist conditions to obtain the solid waste coal gangue base polymer backfill material.

4. The method for preparing a polymer backfill material for solid waste coal gangue base according to claim 2, characterized in that, The curing conditions in step 2 are a temperature of 20±2℃ and a relative humidity of not less than 95%.

5. The application of the all-solid waste coal gangue base polymer backfill material as described in claim 2 in mine backfilling.

6. The application according to claim 5, characterized in that, The solid waste coal gangue base polymer backfill material is used as a cemented filling material for the goaf of the mine.