A cementitious material for mine backfilling and its preparation method

Abstract

This invention discloses a mine backfill cementitious material and its preparation method. The mine backfill cementitious material of this invention comprises the following components in the following mass ratios: high belite sulfoaluminate cement clinker: 3-8 wt%; high free calcium silicate cement clinker: 1-3 wt%; granulated blast furnace slag powder or granulated blast furnace slag: 74-85 wt%; gypsum: 10-18 wt%. Compared with other paste-like backfill materials of the same strength, the cementitious material of this invention solves the problems of poor activation effect, poor mechanical properties affecting the mine backfilling effect, and high cost due to large amount of cementitious material used in existing mine backfill cementitious materials. At the same time, it not only reduces the proportion of cementitious material used, but also fully meets the requirements of mine backfilling projects.

Description

Technical Field

[0001] This invention relates to the field of mine backfilling technology, specifically to a mine backfilling cementitious material and its preparation method. Background Technology

[0002] Paste backfilling mining technology is used in both metallic and non-metallic mining. This technology involves preparing solid waste into a paste-like slurry that does not require dehydration, and then transporting it to the underground goaf through a material transport system for open, timely, and appropriate backfilling. This technology has the following advantages: firstly, it protects safety and improves the safety assurance of mine operations; secondly, it protects resources and increases the recovery rate of mineral resources; and thirdly, it protects the environment, reducing the degree of damage to the surface caused by mining and reducing the emission of solid waste from mines.

[0003] The preparation of paste-like slurries requires the use of cementing materials. GB / T 51450-2022, "Technical Standard for Backfilling Engineering in Metal and Non-metal Mines," defines cementing materials as: substances that, under physical and chemical action, can transform from a slurry into a solid, stone-like substance and can bind other materials to form a composite solid with a certain mechanical strength. NB / T11434.5—2023, "Coal Mine Paste Backfilling Part 5: Technical Requirements for Cementing Materials," defines cementing materials as: hydraulically mixed materials made from materials with potential hydraulic properties, activating materials, and other functional additives, including but not limited to general-purpose Portland cement (Portland cement, ordinary Portland cement, slag Portland cement, pozzolanic Portland cement, fly ash Portland cement, and composite Portland cement), medium-heat Portland cement, low-heat Portland cement, masonry cement, steel slag Portland cement, magnesium slag Portland cement, alkali slag cementing materials, gypsum slag cementing materials, lime-pozzolanic cementing materials, and geopolymer cementing materials, etc. To reduce costs and dispose of solid waste, clinker-free or low-clinker cement is widely used.

[0004] CN 114940600 A discloses a solid waste backfill material and its preparation method. The gel material includes desulfurized gypsum, fly ash, slag, steel slag, magnesium slag, carbide slag, water-reducing agent, water-retaining dispersant, and alkaline activator. The aggregate is tailings. Its beneficial effects are: it rationally utilizes the theory of synergistic complementarity of chemical components from multiple solid waste sources; under the action of the alkaline activator, the silicon-rich and calcium-rich phases in the slag and fly ash structures react to generate higher-strength AFm crystals; the water-retaining dispersant effectively solves the segregation and bleeding problems of the solid waste backfill material, giving it good water retention and uniform dispersion; and the addition of an appropriate amount of fly ash allows it to exert a ball-bead effect, increasing the fluidity of the backfill slurry. This technology uses solid waste to produce the gelling material and employs multiple activation technologies, including alkaline activation and sulfate activation.

[0005] CN202110267272.8 discloses a cement-based backfill material containing various solid wastes, its preparation method, and its application. The backfill material of this invention is composed of the following raw materials in the indicated mass percentages: 5%-14% desulfurized gypsum, 22%-35% fly ash, 24%-35% water-quenched slag, 5%-6% cement, and 25wt%-35% tap water. By utilizing three solid wastes—desulfurized gypsum, fly ash, and water-quenched slag—with a small amount of cement to prepare the backfill, the environmental pollution problem caused by solid waste accumulation is solved. Simultaneously, the solid wastes, cement, and water in the backfill material undergo a hydration reaction to generate a large amount of hydration products, thereby forming a high-strength backfill that can meet the strength requirements of backfill in underground mining. This technology uses desulfurized gypsum as sulfate activation and ordinary Portland cement (strength grade 42.5R or 52.5). Calcium hydroxide produced during the hydration process of ordinary cement is used as alkali activation. Overall, it has a certain activation effect, but the activation effect is far lower than the existing advanced levels. As a filling material, solid waste materials have very low utilization efficiency.

[0006] In recent years, a new type of supersulfate cement has emerged. Based on traditional gypsum-slag cement, it incorporates a special cement clinker, high-belite sulfoaluminate clinker, as an activating material, significantly improving the activating effect of the slag. This results in a substantial increase in both the early and later strength of the cement, leading to the standard T / CBMF 192—2022, "Slag Sulphoaluminate Cement." This cement is a hydraulic cementitious material made from sulfoaluminate cement clinker, granulated blast furnace slag, and anhydrite, exhibiting low heat of hydration and high flexural strength. The sulfoaluminate cement clinker primarily consists of anhydrous calcium sulfoaluminate and dicalcium silicate, with the sum of the contents (mass fraction) of anhydrous calcium sulfoaluminate and dicalcium silicate not less than 60%, and the contents (mass fraction) of both anhydrous calcium sulfoaluminate and dicalcium silicate not less than 25 wt%. The composition of the sulfoaluminate cement clinker is 2-10 wt%, anhydrite 8-25%, and granulated blast furnace slag (powder) 65-90%.

[0007] In backfilling projects in metal and non-metal mines, based on the characteristics of novel supersulfate cement, slag sulfoaluminate cement was considered as a cementing material to achieve low cementitious material usage, simplified backfilling process, and thus reduced costs. However, in actual use, it was found that due to the low cement-to-sand ratio, sometimes reaching 1:11 or even lower, and the very high water-to-cement ratio, usually greater than 4.7, coupled with the fineness of the tailings, the early and later strength of the backfill paste was significantly reduced. Summary of the Invention

[0008] The purpose of this invention is to provide a mine backfill cementitious material and its preparation method, so as to solve the problems of poor activation effect, poor mechanical properties affecting the mine backfilling effect, and high cost due to large amount of cementitious material used in the prior art.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0010] On the one hand, a mine backfill cementitious material is provided, comprising the following components in the following mass ratio:

[0011] High belite sulfoaluminate cement clinker: 3-8 wt%;

[0012] High free calcium silicate cement clinker: 1-3 wt%;

[0013] Granulated blast furnace slag powder or granulated blast furnace slag: 74-85 wt%;

[0014] Gypsum: 10–18 wt%.

[0015] Furthermore, the mineral composition of the high-belite sulfoaluminate cement clinker includes C2S, C4AF, CaSO4 and f-CaO, among which The sum of the mass fractions of C2S and C2S is ≥60wt%, and The mass fraction of C2S is ≥25wt%, the mass fraction of C4AF is 1-10wt%, the mass fraction of CaSO4 is 2-24wt%, and the mass fraction of f-CaO is 0-3wt%.

[0016] Furthermore, the mineral composition of the high-free-calcium silicate cement clinker includes f-CaO, C3S, C2S, C3A, C4AF, and CaSO4, wherein the mass fraction of f-CaO is 42–55 wt%. The mass fraction of C3S is 0–3 wt%, the sum of the mass fractions of C3S and C2S is 22–45 wt%, the sum of the mass fractions of C3A and C4AF is 5–20 wt%, and the mass fraction of CaSO4 is 0–3 wt%.

[0017] Furthermore, the granulated blast furnace slag powder meets the quality requirements of GB / T 18046-2017 "Granulated blast furnace slag powder for use in cement, mortar and concrete", and is grade S95.

[0018] Furthermore, the granulated blast furnace slag meets the quality requirements of GB / T 203 "Granulated blast furnace slag for use in cement".

[0019] Furthermore, the gypsum includes at least one of dihydrate gypsum, anhydrite, desulfurized gypsum, and phosphogypsum.

[0020] Furthermore, the desulfurized gypsum or the phosphogypsum needs to be modified, specifically by calcining at 600–800°C for 10–20 minutes.

[0021] On the other hand, a method for preparing a cementitious material for mine backfilling is provided, which involves separately grinding high-belite sulfoaluminate cement clinker, high-free-calcium silicate cement clinker, granulated blast furnace slag powder or granulated blast furnace slag, and gypsum, weighing them according to a mass ratio, and then uniformly mixing them; or weighing high-belite sulfoaluminate cement clinker, high-free-calcium silicate cement clinker, granulated blast furnace slag powder or granulated blast furnace slag, and gypsum according to a mass ratio, mixing them uniformly, and grinding them to a specific surface area ≥ 420 m². 2 / kg, to obtain mine filling cementitious material.

[0022] Furthermore, high belite sulfoaluminate cement clinker, high free calcium silicate cement clinker, granulated blast furnace slag powder or granulated blast furnace slag, and gypsum are ground separately, weighed according to the mass ratio, and then uniformly mixed to obtain a mine filling cementitious material.

[0023] Furthermore, the specific surface area of ​​the high-belite sulfoaluminate cement clinker after grinding is ≥420 m². 2 / kg, the specific surface area of ​​the high free calcium silicate cement clinker after grinding is ≥380m² 2 / kg, the specific surface area of ​​the granulated blast furnace slag powder or the granulated blast furnace slag powder after grinding is ≥420m². 2 / kg, the specific surface area of ​​the gypsum powder after grinding is ≥420m² 2 / kg.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1. The cement clinker used in the cementitious material of this invention is used in small amounts. Under normal circumstances, the appropriate admixture is about 7%, resulting in low carbon emissions.

[0026] 2. The active energy of the slag used in the cementitious material of this invention is effectively activated, resulting in a significant increase in early and late strength. The strength can be increased by at least 50% based on the existing technology level. The amount of cementitious material used to achieve the same filling strength of the paste material is significantly reduced, saving the amount of cementitious material used and helping to save costs.

[0027] 3. The raw material components of the cementitious material of this invention are relatively few and abundant, making production and use relatively simple. When using the cementitious material to prepare paste filling materials, it exhibits good mixing properties, rapid early strength development, and steady strength growth in the later stages, allowing for a reduction or elimination of the amount of admixtures required. In areas with scarce resources around the mine, such as a lack of fly ash, steel slag, magnesium slag, and ferromanganese slag, raw material acquisition is easy, and production is more flexible.

[0028] 4. The cementitious material of this invention is made from granulated blast furnace slag powder or granulated blast furnace slag combined with cement clinker and gypsum. During the hydration reaction, due to the suitable concentration and alkalinity of various ions in the hydration environment, ettringite is generated relatively quickly. At the same time, the dissolution rate of ions in the glassy body of granulated blast furnace slag powder or granulated blast furnace slag also accelerates. The ettringite particles formed after the dissolved ions in the glassy body participate in the reaction fill the skeleton of unreacted ions, mutually wrapping and interpenetrating to form a dense structure. This results in a much higher early strength and later strength compared to the early strength of cementitious materials activated by other industrial waste residues, and the setting and hardening time is also greatly shortened. In its early stages, the high-belite sulfoaluminate cement clinker and high-free-calcium silicate cement clinker provide a suitable alkaline environment for the formation of calcium hydroxide through the hydration of f-CaO, resulting in accelerated hydration of the high-belite sulfoaluminate cement clinker and rapid formation of ettringite. The main hydration products are AFt and a small amount of CSH gel. In the later stages, granulated blast furnace slag powder or granulated blast furnace slag continues to hydrate, producing CSH, a small amount of hydrotalcite, and other hydrates that fill the early hydrates, increasing density and further improving later-stage strength, exhibiting excellent mechanical properties. Compared with other paste-like fillers of the same strength, the proportion of cementitious material used in this invention is also greatly reduced, fully meeting the needs of mine backfilling projects. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0030] In this invention, the mineral composition of high belite sulfoaluminate cement clinker includes: 28.5wt%, C2S: 46.2wt%, C4AF: 3.5wt%, CaSO4: 8.7wt%, f-CaO: 2.4wt%.

[0031] In this invention, the mineral composition of the high-free-calcium silicate cement clinker includes f-CaO: 47.2 wt%, C2S+C3S: 27.2 wt%, 2.1wt%, C3A+C4AF: 17.6wt%, CaSO4: 0.5wt%.

[0032] In this invention, the granulated blast furnace slag meets the quality requirements of GB / T 18046-2017 "Granulated blast furnace slag powder for use in cement, mortar and concrete".

[0033] In this invention, the anhydrite is commercially available anhydrite.

[0034] In this embodiment of the invention, the specific surface area of ​​the high-belite sulfoaluminate cement clinker after grinding is ≥420 m². 2 / kg, the specific surface area of ​​high free calcium silicate cement clinker after grinding is ≥380m² 2 / kg, the specific surface area of ​​granulated blast furnace slag powder after grinding is ≥420m² 2 / kg, specific surface area of ​​ground anhydrite powder ≥420m² 2 / kg.

[0035] Example 1

[0036] As a preferred embodiment of the present invention, the specific composition of the mine backfill cementitious material of this embodiment is shown in Table 1 below:

[0037] Table 1

[0038]

[0039]

[0040] High belite sulfoaluminate cement clinker, high free calcium silicate cement clinker, granulated blast furnace slag powder, and anhydrite were ground separately, weighed according to the mass ratio shown in Table 1, and then uniformly mixed to obtain the mine filling cementitious material of this embodiment.

[0041] Example 2

[0042] As a preferred embodiment of the present invention, the specific composition of the mine backfill cementitious material of this embodiment is shown in Table 2 below:

[0043] Table 2

[0044] Components Mass ratio (wt%) High Belite sulfoaluminate cement clinker 3.50 High free calcium silicate cement clinker 1.50 Granulated blast furnace slag powder 80.00 Hard plaster 15.00

[0045] High belite sulfoaluminate cement clinker, high free calcium silicate cement clinker, granulated blast furnace slag powder, and anhydrite were ground separately, weighed according to the mass ratio shown in Table 2, and then uniformly mixed to obtain the mine filling cementitious material of this embodiment.

[0046] Comparative Example 1

[0047] The specific composition of the cementitious material in this comparative example is shown in Table 3, and the rest are the same as in Example 1.

[0048] Table 3

[0049] Components Mass ratio (wt%) High Belite sulfoaluminate cement clinker 2.00 High free calcium silicate cement clinker 1.50 Granulated blast furnace slag powder 81.50 Hard plaster 15.00

[0050] Comparative Example 2

[0051] The specific composition of the cementitious material in this comparative example is shown in Table 4, and the rest are the same as in Example 1.

[0052] Table 4

[0053] Components Mass ratio (wt%) High Belite sulfoaluminate cement clinker 8.50 High free calcium silicate cement clinker 1.50 Granulated blast furnace slag powder 75.00 Hard plaster 15.00

[0054] Comparative Example 3

[0055] The specific composition of the cementitious material in this comparative example is shown in Table 5, and the rest is the same as in Example 1.

[0056] Table 5

[0057] Components Mass ratio (wt%) High Belite sulfoaluminate cement clinker 3.50 High free calcium silicate cement clinker 4.50 Granulated blast furnace slag powder 77.00 Hard plaster 15.00

[0058] Comparative Example 4

[0059] The specific composition of the cementitious material in this comparative example is shown in Table 6, and the rest is the same as in Example 1.

[0060] Table 6

[0061] Components Mass ratio (wt%) High Belite sulfoaluminate cement clinker 3.50 High free calcium silicate cement clinker 0.50 Granulated blast furnace slag powder 81.00 Hard plaster 15.00

[0062] Comparative Example 5

[0063] The cementing material used in this comparative example is commercially available P·O 42.5 cement.

[0064] Experimental Example 1

[0065] According to T / MMAC 005-2022 "Cementitious Materials for Cemented Backfilling of Tailings in Metal Mines" and GB / T 17671-2021 "Test Method for Strength of Cement Mortar (ISO Method)", mortar specimens were formed for each example and comparative example, and the compressive strength of the mortar was tested. The test results are shown in Table 7 below.

[0066] Table 7

[0067]

[0068] According to the test results in Table 7:

[0069] (1) The early strength of the cementitious material in the embodiments of the present invention is relatively high. When the proportion of high belite sulfoaluminate cement clinker is too large (Comparative Example 2), the hydrates produced in the initial hydration are excessively coated on the surface of the slag powder, which delays the further hydration of the slag powder; when the proportion of high belite sulfoaluminate cement clinker is too small (Comparative Example 1), the activation effect is weak, which leads to the inability to effectively activate the activity of the slag powder, resulting in lower early and later strength.

[0070] (2) Because the mortar of the paste filling material is relatively small, its tailings are usually finer and the alkalinity in the hydration environment is low. Therefore, a high free calcium silicate cement clinker was used to adjust it. However, if its usage ratio is too high (Comparative Example 3), the early strength is improved, but the later strength growth is suppressed. If the usage ratio is too low (Comparative Example 4), the early and later activation effects will not be ideal.

[0071] (3) Comparative Example 5 uses existing gel material - ordinary silicate cement P·O 42.5 cement. Its later strength development is not as good as that of the embodiments of the present invention, and its clinker usage is also higher than that of the embodiments.

[0072] Experimental Example 2

[0073] The preparation of backfill material test blocks was carried out according to GB / T 51450-2022 "Technical Standard for Backfill Engineering in Metal and Non-metal Mines": Specifically, the cementitious material (6.4 wt%) of each example and comparative example was mixed evenly with phosphate tailings (63.6 wt%) and water (30.0 wt%), and then poured into a mold and vibrated to obtain a paste-like backfill material. The phosphate tailings were phosphate mine tailings with a water content of 26 wt%, and the weight percentage of the main mineral components was: dolomite: 74.2 wt%, quartz: 2.1 wt%, fluorapatite: 13.3 wt%, calcite: 0.7 wt%, and ferrodolithite: 9.7 wt%.

[0074] The compressive strength of each paste filling material was tested according to the methods in JGJ / T 70—2009 "Standard for Basic Performance Test Methods of Building Mortar", T / MMAC 005-2022 "Cementitious Materials for Tailings Filling in Metal Mines" and NB / T 51070-2017 "Test Methods for Paste Filling Materials in Coal Mines". The test results are shown in Table 8 below.

[0075] Table 8

[0076]

[0077] According to the test results in Table 8:

[0078] In Comparative Examples 1 and 2, the amount of high-Belit sulfoaluminate cement clinker added to the cementitious material was too small and too large, respectively, and their performance was far inferior to that of the Examples. Similarly, in Comparative Examples 3 and 4, the amount of high-free calcium silicate cement clinker added to the cementitious material was either too large or too small, and their performance was also inferior to that of the Examples. The activating effect of Comparative Examples 1 to 4 was weaker than that of Examples 1 and 2, and the mechanical properties of the paste filling materials prepared in Examples 1 and 2 were superior to those of Comparative Examples 1 to 4. Furthermore, compared to Comparative Example 5, the later-stage mechanical properties of the paste filling materials prepared in Examples 1 and 2 were also superior to those of paste filling materials prepared with existing gel materials. At the same time, the amount of clinker used in the cementitious material was very small, which is beneficial for cost savings. Therefore, the cementitious material provided by this invention can improve the problem of poor early and later-stage mechanical properties of general filling materials, and at the same time, the material source is abundant, easy to prepare, and the cost savings are significant.

[0079] Finally, it should be noted that the above embodiments are merely preferred embodiments of the present invention used to illustrate the technical solutions of the present invention, and are not intended to limit the invention, nor are they intended to limit the patent scope of the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention. That is to say, any changes or refinements made to the main design concept and spirit of the present invention that are not of substantial significance, but whose technical problems are still consistent with the present invention, should be included within the protection scope of the present invention. In addition, the direct or indirect application of the technical solutions of the present invention to other related technical fields are similarly included within the patent protection scope of the present invention.

Claims

1. A mine filling cementitious material, characterized in that, The following components are included in the following mass ratio: High belite sulfoaluminate cement clinker: 3~8wt%; High free calcium silicate cement clinker: 1~3wt%; Granulated blast furnace slag powder or granulated blast furnace slag: 74~85wt%; Gypsum: 10~18wt% The mineral composition of the high belite sulfoaluminate cement clinker includes C2S, C4AF, CaSO4 and f-CaO, among which The sum of the mass fractions of C2S and C2S is ≥60wt%, and The mass fraction of C2S is ≥25wt%, the mass fraction of C4AF is 1-10wt%, the mass fraction of CaSO4 is 2-24wt%, and the mass fraction of f-CaO is 0-3wt%. The mineral composition of the high free calcium silicate cement clinker includes f-CaO, The compounds are C3S, C2S, C3A, C4AF, and CaSO4, wherein the mass fraction of f-CaO is 42–55 wt%. The mass fraction of C3S is 0–3 wt%, the sum of the mass fractions of C3S and C2S is 22–45 wt%, the sum of the mass fractions of C3A and C4AF is 5–20 wt%, and the mass fraction of CaSO4 is 0–3 wt%.

2. The mine backfill cementitious material according to claim 1, characterized in that, The granulated blast furnace slag powder meets the quality requirements of GB / T 18046-2017 "Granulated blast furnace slag powder for use in cement, mortar and concrete" and is grade S95.

3. The mine backfill cementitious material according to claim 1, characterized in that, The granulated blast furnace slag meets the quality requirements of GB / T 203-2008 "Granulated blast furnace slag for use in cement".

4. The mine backfill cementitious material according to claim 1, characterized in that, The gypsum includes at least one of dihydrate gypsum, anhydrite, desulfurized gypsum, and phosphogypsum.

5. The mine backfill cementitious material according to claim 4, characterized in that, The desulfurized gypsum or the phosphogypsum needs to be modified, specifically by calcining at 600~800℃ for 10~20 minutes.

6. A method for preparing a mine backfill cementitious material according to any one of claims 1 to 5, characterized in that, High-Belit sulfoaluminate cement clinker, high-free-calcium silicate cement clinker, granulated blast furnace slag powder or granulated blast furnace slag, and gypsum are ground separately, weighed according to the mass ratio, and then uniformly mixed. Alternatively, high-Belit sulfoaluminate cement clinker, high-free-calcium silicate cement clinker, granulated blast furnace slag powder or granulated blast furnace slag, and gypsum are weighed according to the mass ratio, mixed uniformly, and ground until the specific surface area is ≥420m². 2 / kg, to obtain mine filling cementitious material.

7. The method for preparing a mine backfill cementitious material according to claim 6, characterized in that, High belite sulfoaluminate cement clinker, high free calcium silicate cement clinker, granulated blast furnace slag powder or granulated blast furnace slag, and gypsum are ground separately, weighed according to the mass ratio, and then uniformly mixed to obtain a mine filling cementitious material.

8. The method for preparing a mine backfill cementitious material according to claim 7, characterized in that, The specific surface area of ​​the high belite sulfoaluminate cement clinker after grinding is ≥420m². 2 / kg, the specific surface area of ​​the high free calcium silicate cement clinker after grinding is ≥380m² 2 / kg, the specific surface area of ​​the granulated blast furnace slag powder or the granulated blast furnace slag powder after grinding is ≥420m². 2 / kg, the specific surface area of ​​the gypsum powder after grinding is ≥420m² 2 / kg.

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