Gel material for coal gangue filling body and preparation method thereof

Abstract

The invention belongs to the technical field of coal gangue filling bodies, and provides a gel material for a coal gangue filling body and a preparation method of the gel material. The gel material for the coal gangue filling body comprises clay powder, an active agent, aluminum sulfate and sodium carboxymethyl cellulose in specific parts by mass. The soft clay is subjected to microwave heat treatment and then mixed with the active agent, the aluminum sulfate and the sodium carboxymethyl cellulose to obtain the gel material, the raw materials are non-toxic and pollution-free and are weakly acidic or neutral, the hydration reaction can be completed according to the ion exchange behavior of the raw materials, the pH value of coal gangue slurry does not need to be increased, and the preparation process is simple. The final pH value of the coal gangue filling body is ensured to meet the requirement of underground water quality; (-Si-O-Al-O-) n polymer skeleton gel, hydrated calcium silicate gel, hydrated calcium aluminate gel and hydrated calcium aluminosilicate gel are continuously generated in the hardening process of the cementing material, heavy metal ions in the coal gangue are adsorbed and fixedly sealed in situ, and the long-term strength meets the filling requirement of the coal gangue.

Description

Technical Field

[0001] This invention relates to the field of coal gangue backfill technology, and in particular to a gel material for coal gangue backfill and its preparation method. Background Technology

[0002] Coal gangue is a typical bulk industrial solid waste generated from coal mining, with annual emissions exceeding 100 million tons. Long-term stockpiling not only occupies vast amounts of land but also easily leads to environmental problems such as spontaneous combustion, dust pollution, and heavy metal leaching. Currently, underground backfilling of coal gangue has become an effective way to dispose of it. In the field of underground backfilling in mines, traditional backfilling materials typically use ordinary Portland cement as the core cementing component, accounting for approximately 60-75% of the total cost of backfilling materials. The high cost of cementing materials significantly weakens the feasibility of backfilling mining methods, especially for low-grade ore bodies and deep mining bodies. The long-term excessive alkalinity of cement-based backfilling materials (the pH value of the leachate is usually higher than 11.5) easily induces secondary environmental risks such as alkali corrosion of surrounding rocks and deterioration of groundwater quality, making it difficult to meet the requirements of green mines for both mechanical and environmental control indicators.

[0003] To address this issue, efforts have been made to explore the use of industrial solid waste to partially replace cement in the construction of solid waste-based backfill material systems. For example, patent CN202210953307.8, "A Coal Gangue-Landfill Ash-Based Cemented Backfill Material for Mining and Its Preparation Method and Application," utilizes coal gangue, landfill ash, ash flushing wastewater, desulfurization wastewater, early-strength agents, and retarder to prepare underground backfill material. This material exhibits a 28-day compressive strength of no less than 5 MPa, demonstrating excellent mechanical properties. It can effectively suppress severe deformation of the overlying strata after coal mining, significantly reducing disturbance and damage to the aquifer structure and surface environment. While this method constructs a solid waste-based backfill material system, the poor chemical compatibility of the raw materials can easily lead to adverse reactions. Even if short-term strength meets standards, long-term leaching toxicity may exceed limits, especially under groundwater infiltration, where heavy metals and salts are slowly released, posing significant environmental risks. Patent CN202210223822.0, "A Backfill Material Mixed with Red Mud, Desulfurized Gypsum, and Slag and Its Preparation Method," describes a method that uses red mud and desulfurized gypsum to composite-activated granulated blast furnace slag and coal gangue as backfill aggregate to prepare a paste-like backfill material. This method can not only improve the ore recovery rate but also promote the functional restoration of damaged land in mining areas. However, under conditions of groundwater infiltration, wet-dry cycles, or temperature changes, the backfill material still faces risks of micro-cracks, strength decay, and ion leaching, affecting the long-term support effect.

[0004] It is evident that most existing backfill technologies focus on the mechanical properties of the backfill, neglecting the regulation of its long-term chemical stability. Under the service conditions of underground engineering, the backfill is in long-term contact with the surrounding rock and groundwater. If the pH value of its leachate remains highly alkaline, it can easily disturb the mineral phase balance of the rock and soil media, promote the dissolution of heavy metal ions, and seriously damage the underground ecological restoration of the mining area.

[0005] Therefore, it is of great significance to construct a low-cost and environmentally friendly solid waste-based backfilling system, a new type of backfilling material that does not require high-temperature treatment, does not rely on strong alkali activation, and can precisely control the pH value of the leachate to the weakly alkaline range (pH value≈8), and achieve efficient backfilling of coal gangue while ensuring a 28-day strength of ≥12MPa, and to promote the large-scale and high-value application of coal gangue in mine backfilling scenarios. Summary of the Invention

[0006] The purpose of this invention is to provide a gel material for coal gangue backfill and its preparation method, addressing the shortcomings of existing technologies.

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a gel material for coal gangue backfill, comprising the following raw materials in parts by weight: 65-80 parts clay powder, 15-25 parts activator, 2-5 parts aluminum sulfate, and 0.5-2 parts sodium carboxymethyl cellulose.

[0008] Preferably, the clay powder has a particle size of ≤500 mesh.

[0009] Preferably, the clay powder is obtained by microwave heat treatment of soft clay.

[0010] Preferably, the soft clay comprises kaolin and / or bentonite.

[0011] Preferably, the soft clay has a particle size ≤45μm and a pH value ≤7.

[0012] Preferably, the microwave heat treatment temperature is 400~500℃ and the microwave heat treatment time is 12~24h.

[0013] Preferably, the activator comprises calcium silicate and / or monocalcium aluminate, and the particle size of the activator is ≤10μm.

[0014] The present invention also provides a method for preparing the gel material for coal gangue backfill, wherein clay powder, activator, aluminum sulfate and sodium carboxymethyl cellulose are mixed evenly to obtain the material.

[0015] The beneficial effects of this invention are: 1) This invention involves mixing soft clay with an activator, aluminum sulfate, and sodium carboxymethyl cellulose after microwave heat treatment to prepare a gel material for coal gangue backfill. The raw materials themselves are non-toxic and non-polluting, exhibiting weak acidity or neutrality. The hydration reaction of the gel material can be completed based on its own ion exchange behavior, without needing to increase the pH value of the coal gangue slurry, thus ensuring that the final pH value of the coal gangue backfill meets the requirements of groundwater quality. During the hardening process of the gel material of this invention, (-Si-O-Al-O-) are continuously generated. n Polymer-based backbone gels, hydrated calcium silicate (CSH) gels, hydrated calcium aluminate (CAH) gels, and hydrated calcium aluminosilicate (CASH) gels can adsorb and in-situ solidify heavy metal ions in coal gangue, enabling the coal gangue backfill to meet the requirements of groundwater quality in terms of pH value and ion leaching concentration, while also meeting the long-term strength requirements for coal gangue backfilling and exhibiting good fluidity of the backfill slurry. The preparation methods are simple, low-cost, and suitable for mass production.

[0016] 2) After microwave heat treatment, the soft clay is dehydrated of free water and structural water, and after grinding, it forms highly active amorphous metakaolin. During the filling process, the amorphous metakaolin and aluminum sulfate first depolymerize to produce active SiO4. 4- AlO4 5- Ions, active SiO4 4- With AlO4 5- Ions are linked by "bridging oxygen" to form a three-dimensional network structure (-Si-O-Al-O-). n The polymer-based skeleton gel improves the compressive strength of the filling material; the active agent calcium silicate or monocalcium aluminate rapidly hydrates in the coal gangue filling material, forming hydrated calcium silicate (CSH) gel, hydrated calcium aluminate (CAH) gel, and hydrated calcium aluminosilicate (CASH) gel. These three components form a tight crystalline network structure, binding the non-cementing coal gangue together and achieving early strength; excess SiO4... 4- AlO4 5- SO4 produced by the reaction of ions with aluminum sulfate 2- Ionic reactions form ettringite, which further enhances the strength of the filling material; sodium carboxymethyl cellulose is adsorbed on the surface of coal gangue, changing the hydrophilic properties of the coal gangue particles, improving the dispersion effect of coal gangue in water, and significantly improving the fluidity of the coal gangue slurry. Detailed Implementation

[0017] This invention provides a gel material for coal gangue backfill, comprising the following raw materials in parts by weight: 65-80 parts clay powder, 15-25 parts activator, 2-5 parts aluminum sulfate, and 0.5-2 parts sodium carboxymethyl cellulose.

[0018] In this invention, the gel material for the coal gangue backfill comprises, by weight, the following raw materials: 65-80 parts of clay powder, preferably 68-76 parts, more preferably 70-74 parts; 15-25 parts of activator, preferably 18-22 parts, more preferably 20 parts; 2-5 parts of aluminum sulfate, preferably 3-4 parts, more preferably 3.5 parts; and 0.5-2 parts of sodium carboxymethyl cellulose, preferably 0.8-1.5 parts, more preferably 1-1.2 parts.

[0019] In this invention, the particle size of the clay powder is preferably ≤500 mesh, more preferably ≤480 mesh, and even more preferably ≤450 mesh.

[0020] In this invention, the clay powder is preferably obtained from soft clay through microwave heat treatment.

[0021] In this invention, the soft clay preferably comprises kaolin and / or bentonite.

[0022] In this invention, the particle size of the soft clay is preferably ≤45μm, more preferably ≤42μm, and even more preferably ≤40μm; the pH value of the soft clay is preferably ≤7, more preferably ≤6.5, and even more preferably ≤6.

[0023] In this invention, the microwave heat treatment temperature is preferably 400~500℃, more preferably 420~480℃, and even more preferably 450℃; the microwave heat treatment time is preferably 12~24h, more preferably 14~20h, and even more preferably 16~18h.

[0024] In this invention, the activator preferably comprises calcium silicate and / or monocalcium aluminate, and the particle size of the activator is preferably ≤10μm, more preferably ≤9μm, and even more preferably ≤8μm.

[0025] In this invention, the purity of the sodium carboxymethyl cellulose is preferably ≥90%, more preferably ≥92%, and even more preferably ≥95%.

[0026] The present invention also provides a method for preparing the gel material for coal gangue backfill, wherein clay powder, activator, aluminum sulfate and sodium carboxymethyl cellulose are mixed evenly to obtain the material.

[0027] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0028] Example 1

[0029] The gel material for coal gangue backfill, by weight, is composed of the following raw materials: 65 parts clay powder, 25 parts activator, 2 parts aluminum sulfate, and 0.5 parts sodium carboxymethyl cellulose. The clay powder is prepared by microwaving kaolin with a particle size ≤45μm and a pH of 7 at 400℃ for 18 hours, followed by grinding and passing through a 500-mesh sieve. The activator is calcium silicate (particle size ≤8μm). The purity of the sodium carboxymethyl cellulose is ≥90%.

[0030] The gel material for coal gangue backfill is obtained by mixing clay powder, activator, aluminum sulfate and sodium carboxymethyl cellulose evenly.

[0031] Example 2

[0032] The gel material for coal gangue backfill, by weight, is composed of the following raw materials: 65 parts clay powder, 25 parts activator, 2 parts aluminum sulfate, and 0.5 parts sodium carboxymethyl cellulose. The clay powder is prepared by microwave heat treatment of bentonite with a particle size ≤45μm and a pH of 7 at 400℃ for 24 hours, followed by grinding and passing through a 500-mesh sieve. The activator is monocalcium aluminate (with a particle size ≤8μm). The purity of sodium carboxymethyl cellulose is ≥90%.

[0033] The gel material for coal gangue backfill is obtained by mixing clay powder, activator, aluminum sulfate and sodium carboxymethyl cellulose evenly.

[0034] Example 3

[0035] The gel material for coal gangue backfill, by mass, is composed of the following raw materials: 80 parts clay powder, 15 parts activator, 2 parts aluminum sulfate, and 2 parts sodium carboxymethyl cellulose. The clay powder is prepared by microwaving kaolin (particle size ≤ 42 μm, pH 6.5) and bentonite (particle size ≤ 42 μm, pH 6.5) at a mass ratio of 1:1 at 400℃ for 24 h, followed by grinding and passing through a 500-mesh sieve. The activator is a 1:1 mass ratio of calcium aluminate (particle size ≤ 9 μm) and calcium silicate (particle size ≤ 9 μm). The purity of the sodium carboxymethyl cellulose is ≥ 90%.

[0036] The gel material for coal gangue backfill is obtained by mixing clay powder, activator, aluminum sulfate and sodium carboxymethyl cellulose evenly.

[0037] Example 4

[0038] The gel material for coal gangue backfill, by mass, is composed of the following raw materials: 69 parts clay powder, 23 parts activator, 3 parts aluminum sulfate, and 0.9 parts sodium carboxymethyl cellulose. The clay powder is prepared by microwave heat treatment of bentonite with a particle size ≤40μm and a pH of 6 at 475℃ for 18 hours, followed by grinding and passing through a 500-mesh sieve. The activator is a 1:2 mass ratio of calcium aluminate (particle size ≤10μm) and calcium silicate (particle size ≤10μm). The purity of the sodium carboxymethyl cellulose is ≥90%.

[0039] The gel material for coal gangue backfill is obtained by mixing clay powder, activator, aluminum sulfate and sodium carboxymethyl cellulose evenly.

[0040] Example 5

[0041] The gel material for coal gangue backfill, by mass, is composed of the following raw materials: 73 parts clay powder, 20 parts activator, 3.5 parts aluminum sulfate, and 1.3 parts sodium carboxymethyl cellulose. The clay powder is prepared by microwave heat treatment of kaolin with a particle size ≤40μm and a pH of 6 at 425℃ for 18 hours, followed by grinding and passing through a 500-mesh sieve. The activator is a 1:2 mass ratio of calcium aluminate (particle size ≤9μm) and calcium silicate (particle size ≤9μm). The purity of the sodium carboxymethyl cellulose is ≥90%.

[0042] The gel material for coal gangue backfill is obtained by mixing clay powder, activator, aluminum sulfate and sodium carboxymethyl cellulose evenly.

[0043] Example 6

[0044] The gel material for coal gangue backfill, by weight, consists of the following raw materials: 69 parts clay powder, 18 parts activator, 4.5 parts aluminum sulfate, and 1.6 parts sodium carboxymethyl cellulose. The clay powder is prepared by microwaving kaolin (particle size ≤42μm, pH 6.5) and bentonite (particle size ≤42μm, pH 6.5) at a mass ratio of 1:1 at 450℃ for 20 hours, followed by grinding and passing through a 500-mesh sieve. The activator is calcium silicate (particle size ≤10μm). The purity of sodium carboxymethyl cellulose is ≥90%.

[0045] The gel material for coal gangue backfill is obtained by mixing clay powder, activator, aluminum sulfate and sodium carboxymethyl cellulose evenly.

[0046] Example 7

[0047] The gel material for coal gangue backfill, by weight, consists of the following raw materials: 76 parts clay powder, 18 parts activator, 5 parts aluminum sulfate, and 1.6 parts sodium carboxymethyl cellulose. The clay powder is prepared by microwaving kaolin (particle size ≤ 40 μm, pH 7) and bentonite (particle size ≤ 40 μm, pH 7) at a mass ratio of 1:1 at 500℃ for 20 h, followed by grinding and passing through a 500-mesh sieve. The activator is monocalcium aluminate (particle size ≤ 10 μm). The purity of sodium carboxymethyl cellulose is ≥ 90%.

[0048] The gel material for coal gangue backfill is obtained by mixing clay powder, activator, aluminum sulfate and sodium carboxymethyl cellulose evenly.

[0049] Comparative Example 1

[0050] The active agent in Example 1 is omitted, and everything else is the same as in Example 1.

[0051] Comparative Example 2

[0052] The activator in Example 1 was replaced with silicate cement PO42.5, and everything else was the same as in Example 1.

[0053] Comparative Example 3

[0054] The kaolin in Example 1 was replaced with bauxite, and everything else was the same as in Example 1.

[0055] Comparative Example 4

[0056] The difference from Example 1 is that the clay powder is prepared by microwaving kaolin with a particle size ≤45μm and a pH value of 7 at 600℃ for 12h, then grinding and passing it through a 500-mesh sieve to obtain clay powder.

[0057] The coal gangue backfill gel materials prepared in Examples 1-7 and Comparative Examples 1-4 were mixed with coal gangue aggregate (sourced from Yulin, Shaanxi Province, with a particle size ≤12mm) and water at a mass ratio of 2:6:0.5. Samples were prepared according to JGJ / T70-2009. The slump and compressive strength of the backfill slurry after 28 days of curing were measured. The ion concentration of the leachate after 28 days of curing was tested according to HJ 557-2010 to determine whether it met the Class III standard in GB / T 14848-2017. The test results are shown in Table 1.

[0058] Table 1. Test results of filling materials

[0059] As shown in Table 1, the fillings in Examples 1-7 exhibit excellent compressive strength and are neutral or weakly acidic. In Comparative Example 1, the activator was omitted, and in Comparative Example 2, the activator was replaced with silicate cement PO42.5. The compressive strength of the fillings decreased significantly. Furthermore, during the hydration process, silicate cement PO42.5 continuously generated Ca(OH)2 while forming CSH gel, leading to an increase in the pH value of the fillings and excessive alkalinity. In Comparative Example 3, bauxite was used instead of kaolin. Bauxite itself has a stable structure and cannot form highly active amorphous metakaolin after microwave heat treatment. Consequently, it cannot form a polymer skeleton gel with aluminum sulfate, resulting in a decrease in the compressive strength of the fillings. In Comparative Example 4, a higher microwave heat treatment temperature was used. During the high-temperature microwave heat treatment, kaolin crystallized amorphous metakaolin, significantly reducing its activity and hindering the formation of polymer skeleton gel, resulting in a decrease in the strength of the fillings and an increase in the pH value.

[0060] As can be seen from the above embodiments, the present invention provides a gel material for coal gangue backfill, which is made from clay powder, activator, aluminum sulfate, and sodium carboxymethyl cellulose as raw materials. The high-quality clay is subjected to low-temperature microwave heat treatment to obtain clay powder, which is then mixed with the activator, aluminum sulfate, and sodium carboxymethyl cellulose. The hydration reaction of the gel material can be completed based on its own ion exchange behavior, without needing to increase the pH value of the coal gangue slurry, thus ensuring that the final pH value of the coal gangue backfill meets the requirements of groundwater quality. During the hardening process of the gel material, (-Si-O-Al-O-) are continuously generated. n Polymer-based skeleton gels, hydrated calcium silicate (CSH) gels, hydrated calcium aluminate (CAH) gels, and hydrated calcium aluminosilicate (CASH) gels can adsorb and in-situ solidify heavy metal ions in coal gangue, enabling the coal gangue backfill to meet the requirements of groundwater quality in terms of pH value and ion leaching concentration, and to meet the long-term strength requirements of coal gangue backfill.

[0061] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A gel material for coal gangue backfill, characterized in that, By weight, it contains the following ingredients: 65-80 parts clay powder, 15-25 parts activator, 2-5 parts aluminum sulfate, and 0.5-2 parts sodium carboxymethyl cellulose.

2. The gel material for coal gangue backfill as described in claim 1, characterized in that, The clay powder has a particle size of ≤500 mesh.

3. The gel material for coal gangue backfill as described in claim 1 or 2, characterized in that, The clay powder is obtained by microwave heat treatment of soft clay.

4. The gel material for coal gangue backfill as described in claim 3, characterized in that, The soft clay comprises kaolin and / or bentonite.

5. The gel material for coal gangue backfill as described in claim 4, characterized in that, The soft clay has a particle size ≤45μm and a pH value ≤7.

6. The gel material for coal gangue backfill according to claim 4 or 5, characterized in that, The microwave heat treatment temperature is 400~500℃, and the microwave heat treatment time is 12~24h.

7. The gel material for coal gangue backfill according to claim 6, characterized in that, The activator comprises calcium silicate and / or monocalcium aluminate, and the particle size of the activator is ≤10μm.

8. The method for preparing the gel material for coal gangue backfill as described in any one of claims 1 to 7, characterized in that, The clay powder, activator, aluminum sulfate, and sodium carboxymethyl cellulose are mixed evenly to obtain the final product.

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