Phosphogypsum-based filling material and preparation method thereof

Abstract

The invention discloses a phosphogypsum-based filling material and a preparation method thereof, and belongs to the technical field of mine backfilling. The ardealite-based filling material is prepared from the following raw materials in percentage by weight: 60-70% of ardealite, 8-20% of fly ash, 2-8% of sulphoaluminate cement and 2-18% of slag powder. The invention also discloses a preparation method of the phosphogypsum-based filling material. The ardealite filling material disclosed by the invention realizes efficient resource utilization of a large amount of industrial solid wastes, and the performance of the ardealite filling material meets the technical specification requirements of mine engineering; the problems that a large amount of ardealite is piled up, the utilization rate is low, and the environment is seriously polluted are solved, and the problems that an existing filling material is high in raw material cost, complex in additive variety, high in additive amount, long in setting time, high in bleeding rate and the like are solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of mine backfilling, and in particular relates to a phosphogypsum-based filling material and a preparation method thereof. Background Art

[0002] With the continuous advancement of mining activities and the increasing consumption of mineral resources, the importance of mine backfill technology has become increasingly prominent. This technology is not only a key engineering measure for managing underground goafs and effectively controlling surface subsidence, but also an important means to achieve intensive resource utilization and protect the ecological environment of mining areas. However, in response to the large-scale backfill needs of mines, existing backfill materials mainly rely on resources such as waste rock and tailings. Their binders are mostly based on traditional ordinary Portland cement, and the cement consumption is high, which directly leads to high backfill material costs and is difficult to meet actual engineering needs. Therefore, there is an urgent need to develop new backfill materials that are low-cost, reliable in performance, and environmentally friendly. This has become a research hotspot in the current field of mining engineering.

[0003] In the process of seeking alternative materials, phosphogypsum as a bulk industrial solid waste has come into view. It mainly comes from the production process of wet phosphoric acid and phosphate fertilizers. Its main mineral component is calcium sulfate dihydrate (CaSO4·2H2O), and its content is usually more than 90%. For every ton of phosphoric acid produced, about 4 to 5 tons of phosphogypsum will be produced. The total amount of phosphogypsum stockpiled worldwide is extremely large, with a cumulative total of more than 6 billion tons, but the current comprehensive utilization rate is at a low level, only about 25%. A large amount of phosphogypsum has to be disposed of in open-air storage, which not only occupies precious land resources, but also brings serious environmental risks. During the storage process, the soluble calcium (Ca 2+ ), magnesium (Mg 2+ ) ions significantly increase the hardness of the surrounding water. Furthermore, the migration and concentration of leachable phosphorus (P), fluorine (F), and some heavy metal ions can easily lead to eutrophication of the water environment in the storage yard and its surrounding areas, posing a persistent threat to the ecological environment in and around the mining area. Therefore, how to efficiently and environmentally friendly treat and recycle phosphogypsum has become a major challenge facing both the phosphorus chemical industry and the environmental protection sector.

[0004] Currently, one of the primary approaches to resource utilization for phosphogypsum is to calcine it at 160-180°C, converting it into β-hemihydrate phosphogypsum (building gypsum), which is then used to produce building materials such as gypsum boards and blocks. However, this mainstream process has significant limitations: the calcination process consumes significant energy, resulting in high overall production costs. More importantly, the amount of phosphogypsum that can be absorbed through this process is relatively limited due to the capacity and product performance requirements of the downstream building materials market, resulting in a low overall utilization rate and a failure to fundamentally address the issues of massive stockpiling and environmental pollution.

[0005] Given this background, the use of phosphogypsum as a primary component of mine filling materials demonstrates significant potential and advantages. Not only can it significantly increase the comprehensive utilization rate of phosphogypsum, dispose of industrial solid waste on a large scale, and effectively alleviate the environmental pressures caused by its long-term storage, but it can also significantly reduce the material costs of mine filling operations by replacing traditional sand and gravel aggregates with low-cost phosphogypsum, bringing considerable economic benefits to mining companies. Therefore, the research and development of new mine filling materials based on phosphogypsum has important environmental and economic significance. Summary of the Invention

[0006] The purpose of the present invention is to provide a phosphogypsum-based filling material to solve the problems of large-scale storage of phosphogypsum in the prior art, low utilization rate, and serious environmental pollution, as well as the problems of high raw material cost, complex types of admixtures and high addition amounts, long setting time of filling materials, and high water seepage rate.

[0007] Another object of the present invention is to provide a method for preparing the phosphogypsum-based filling material.

[0008] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0009] The first aspect of the present invention discloses a phosphogypsum-based filling material, the raw materials of which include substances in the following weight ratios: 60-70% phosphogypsum, 8-20% fly ash, 2-8% sulphoaluminate cement, and 2-18% slag powder.

[0010] According to some embodiments of the present invention, the raw materials of the phosphogypsum-based filling material include substances in the following weight ratios: phosphogypsum 70%, fly ash 15%, sulphoaluminate cement 6%, and slag powder 9%.

[0011] The main components of the phosphogypsum of the present invention are calcium sulfate dihydrate (content ≥ 80wt%) and a small amount of hemihydrate gypsum (content ≤ 15wt%). The specific surface area of ​​the phosphogypsum is 300-350kg / m 2 .

[0012] In some embodiments of the present invention, the total content of SiO2 and Al2O3 in the fly ash is ≥75wt%;

[0013] In some embodiments of the present invention, the CaO content in the slag powder is ≥40wt%, and the SiO2 content is ≥25wt%;

[0014] In some embodiments of the present invention, the Al2O3 content in the sulphoaluminate cement clinker is ≥30wt%, and SiO2 is ≤10.5wt%.

[0015] The second aspect of the present invention discloses a method for preparing the above-mentioned phosphogypsum-based filling material, comprising the following steps:

[0016] S1. Raw material pretreatment: The original phosphogypsum is subjected to heat treatment and particle size control; the heat treatment comprises drying the phosphogypsum at a constant temperature of 100-105°C for 12-24 hours to obtain phosphogypsum with a mineral phase composition of 80 wt% or more of dihydrate gypsum and 15 wt% or less of hemihydrate gypsum; the particle size control comprises grinding the heat-treated exothermic phosphogypsum in a ball mill to obtain a specific surface area of ​​300-350 m 2 / kg of phosphogypsum powder; preferably, the grinding time is 1 min;

[0017] S2. Material preparation: Prepare phosphogypsum powder, fly ash, slag powder, and sulphoaluminate cement clinker in proportion;

[0018] S3. Mix phosphogypsum, fly ash, slag powder and sulphoaluminate cement clinker to obtain the filling material.

[0019] The third aspect of the present invention discloses a phosphogypsum-based filling slurry, which is prepared by adding water to the above-mentioned phosphogypsum-based filling material, and the water-to-material ratio of the slurry is 0.55-0.65, preferably 0.6.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] This invention achieves efficient resource utilization of industrial solid waste, such as phosphogypsum. Through optimized formulations, the phosphogypsum content in the filler material system reaches 70%, eliminating the need for expensive chemical admixtures. The resulting slurry boasts a low mass concentration, offering significant cost advantages. Even at a water-to-material ratio of 0.6, there is no bleeding, green body settling, or shrinkage. Mechanical properties, such as material strength, meet mining engineering specifications.

[0022] Secondly, the original phosphogypsum pretreatment process described in the present invention combines simplicity with engineering applicability: the phosphogypsum is dried at 100-105°C for 12-24 hours and then ball-milled for 1 minute, avoiding traditional high-temperature calcination and chemical modification, significantly reducing energy consumption and process complexity. The key innovation lies in the precise control of the amount of hemihydrate gypsum produced, suppressing the risk of late expansion and cracking of high-dosage phosphogypsum-based fillings from the source. The hemihydrate gypsum formed at 105°C exhibits slow-setting properties, with a low early hydration rate and concentrated hydration to form dihydrate gypsum in the later stage. When excessive hemihydrate gypsum is converted, the volume expansion of dihydrate gypsum crystals induces cracking of the hardened body; while the trace amount of dihydrate gypsum generated by the conversion of an appropriate amount of hemihydrate gypsum can effectively fill pores, increase density, and thus optimize mechanical properties. Therefore, it is of great significance to strictly control the content of hemihydrate gypsum in phosphogypsum after heat treatment.

[0023] Finally, in terms of strengthening the core performance of the filling body, the present invention innovatively selected sulphoaluminate cement clinker as the dominant binder of the composite system. Previous studies have shown that silicate cement is not suitable for high sulfate systems because the excessive dihydrate gypsum in the system inhibits the normal hydration process of silicate cement, resulting in slow hydration and low strength of the sample. Sulphoaluminate cement can effectively circumvent this problem: the SO4 released by sulphoaluminate cement clinker and dissolved gypsum 2- A chemical reaction occurs, generating a large amount of ettringite hydration products, significantly accelerating the system's hydration reaction while also promoting the hydration of hemihydrate gypsum in phosphogypsum. This results in rapid hardening of the composite material and a significant increase in early strength, ensuring excellent mechanical properties of the filling.

[0024] In summary, the present invention synergistically optimizes cost, engineering applicability and key physical and mechanical properties through raw material optimization and pretreatment process innovation, realizes the large-scale application of phosphogypsum in filling materials, and provides a feasible technical path for the resource utilization of bulk solid waste. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Attachment Figure 1 The XRD pattern of phosphogypsum after heat treatment and its quantitative analysis results are shown;

[0026] Attachment Figure 2 This is the XRD pattern of the phosphogypsum-based filling material sample after hydration for 28 days. DETAILED DESCRIPTION

[0027] To make the purpose, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0028] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0029] The phosphogypsum described in the embodiments of the present invention is a powdered phosphogypsum obtained by drying and ball-milling the original dihydrate phosphogypsum at 100-110°C. Its main components are calcium sulfate dihydrate (content ≥ 80wt%) and a small amount of hemihydrate gypsum (content ≤ 15wt%). The specific surface area of ​​the phosphogypsum is 300-350kg / m 2 .

[0030] In this embodiment, the Al2O3 content in the sulphoaluminate cement clinker is 31wt%, the SiO2 content is 9.5wt%, and the specification is 52.5 sulphoaluminate cement; the manufacturer is Emeishan Qianghua Special Cement Co., Ltd.

[0031] The chemical compositions of the raw materials in the examples of the present invention are shown in Table 1.

[0032] Table 1 Main chemical composition of raw materials

[0033] Chemical composition CaO MgO <![CDATA[Al2O3]]> <![CDATA[SiO2]]> <![CDATA[SO3]]> <![CDATA[P2O5]]> <![CDATA[Fe2O3]]> <![CDATA[Na2O]]> <![CDATA[K2O]]> F other Phosphogypsum 40.80 0.23 0.97 9.34 45.26 0.82 0.55 0.17 0.28 1.04 0.56 slag powder 43.22 9.36 15.07 26.94 2.24 0.01 0.38 0.94 0.43 / 1.41 fly ash 6.94 1.61 22.02 52.12 1.52 0.27 8.89 2.31 2.38 / 1.94

[0034] Example 1

[0035] This embodiment discloses a preparation method of the phosphogypsum-based filling material of the present invention. The raw materials of the filling material of this embodiment are as follows: phosphogypsum 70%, fly ash 20%, sulphoaluminate cement 8%, and slag powder 2%. The phosphogypsum in this embodiment is obtained by drying the original dihydrate phosphogypsum at 105°C for 12 hours and then ball milling it for 1 minute to obtain powdered phosphogypsum. Its main components are calcium sulfate dihydrate (content ≥80wt%) and a small amount of hemihydrate gypsum (content ≤15wt%). The specific surface area of ​​the phosphogypsum is 300-350kg / m 2 The XRD pattern of phosphogypsum after heat treatment and its quantitative analysis results are shown in the attached Figure 1 The XRD pattern of heat-treated phosphogypsum was quantitatively analyzed using TOPAS software (the reliability factor was 9.28%). Figure 1 The results show that the content of dihydrate gypsum in the heat-treated phosphogypsum is 86.3%; the content of hemihydrate gypsum is 6.6%.

[0036] The preparation method of the phosphogypsum-based filling material of this embodiment is as follows:

[0037] The phosphogypsum powder in the above proportion is evenly mixed with fly ash, sulfoaluminate cement and mineral powder and poured into a mixing pot. First, stir at a stirring rate of 140±5r / min for rotation and 62±5r / min for revolution for 3 minutes. Then, after adding mixing water, stir at a stirring rate of 285±10r / min for rotation and 125±10r / min for revolution for 2 minutes to prepare a slurry. The water-to-material ratio of the slurry is 0.6.

[0038] The XRD spectrum of the phosphogypsum-based filling material sample of this embodiment after hydration for 28 days is shown in the attached figure. Figure 2 As shown. Figure 2It can be seen that the main hydration products of phosphogypsum-based filling materials are dihydrate gypsum and ettringite. This indicates that a large amount of hemihydrate gypsum in the system is fully hydrated to form dihydrate gypsum, while ettringite is mainly a hydration product of sulfoaluminate cement. These two are the main contributors to the filling material's strength. In addition, the diffraction peaks of hemihydrate gypsum still exist in the XRD spectrum, indicating that a very small amount of hemihydrate gypsum in the system remains unhydrated and only serves as a filler, without exerting cementitious properties.

[0039] Example 2

[0040] This embodiment discloses a method for preparing the phosphogypsum-based filling material of the present invention. The filling material of this embodiment comprises the following raw materials: phosphogypsum 70%, fly ash 20%, sulphoaluminate cement 6%, and slag powder 4%.

[0041] The phosphogypsum in this example is prepared by drying raw dihydrate phosphogypsum at 100°C for 24 hours and then ball milling it for 1 minute to obtain a powdered phosphogypsum. Its main components are calcium sulfate dihydrate (content ≥ 80 wt%) and a small amount of hemihydrate gypsum (content ≤ 15 wt%). The specific surface area of ​​the phosphogypsum is 300-350 kg / m 2 .

[0042] The preparation method of the phosphogypsum-based filling material of this embodiment is the same as that of Example 1.

[0043] Example 3

[0044] This embodiment discloses a method for preparing the phosphogypsum-based filling material of the present invention. The filling material of this embodiment comprises the following raw materials: phosphogypsum 70%, fly ash 20%, sulphoaluminate cement 4%, and slag powder 6%.

[0045] The phosphogypsum in this example is prepared by drying raw dihydrate phosphogypsum at 100°C for 24 hours and then ball milling it for 1 minute to obtain a powdered phosphogypsum. Its main components are calcium sulfate dihydrate (content ≥ 80 wt%) and a small amount of hemihydrate gypsum (content ≤ 15 wt%). The specific surface area of ​​the phosphogypsum is 300-350 kg / m 2 .

[0046] Example 4

[0047] This embodiment discloses a method for preparing the phosphogypsum-based filling material of the present invention. The filling material of this embodiment comprises the following raw materials: phosphogypsum 70%, fly ash 20%, sulphoaluminate cement 2%, and slag powder 8%.

[0048] The phosphogypsum in this example is prepared by drying raw dihydrate phosphogypsum at 100°C for 24 hours and then ball-milling it for 1 minute to obtain a powdered phosphogypsum. Its main components are calcium sulfate dihydrate (content ≥ 80 wt%) and a small amount of hemihydrate gypsum (content ≤ 15 wt%). The specific surface area of ​​the phosphogypsum is 300-350 kg / m 2 .

[0049] The preparation method of the phosphogypsum-based filling material of this embodiment is the same as that of Example 1.

[0050] Example 5

[0051] This embodiment discloses a method for preparing the phosphogypsum-based filling material of the present invention. The filling material of this embodiment comprises the following raw materials: 65% phosphogypsum, 15% fly ash, 6% sulphoaluminate cement, and 14% slag powder. The water-to-material ratio is 0.57.

[0052] The phosphogypsum in this example is prepared by drying raw dihydrate phosphogypsum at 110°C for 8 hours and then ball milling it for 1 minute to obtain a powdered phosphogypsum. Its main components are calcium sulfate dihydrate (content ≥ 80 wt%) and a small amount of hemihydrate gypsum (content ≤ 15 wt%). The specific surface area of ​​the phosphogypsum is 300-350 kg / m 2 .

[0053] The total content of SiO2 and Al2O3 in the fly ash in this embodiment is 78wt%;

[0054] In this embodiment, the content of CaO in the slag powder is 43wt%, and the content of SiO2 is 35wt%;

[0055] In this embodiment, the Al2O3 content in the sulphoaluminate cement clinker is 31 wt%, and the SiO2 content is 9.5 wt%.

[0056] The preparation method of the phosphogypsum-based filling material of this embodiment is the same as that of Example 1.

[0057] Comparative Example 1

[0058] Compared with Example 1, this comparative example replaces sulphoaluminate cement with Portland cement, while other conditions remain unchanged. The Portland cement in this ratio is PO42.5R, produced by Jiahua Cement Plant of Jiahua Special Cement Co., Ltd.

[0059] Comparative Example 2

[0060] Compared with Example 2, the content of phosphogypsum in this comparative example is higher. The specific formula is as follows: phosphogypsum 78%, fly ash 12%, sulphoaluminate cement 8%, and slag powder 2%. Other conditions remain unchanged.

[0061] Comparative Example 3

[0062] Compared with Example 1, the drying time of the phosphogypsum in this comparative example is longer, 24 hours. The hemihydrate gypsum content in the treated phosphogypsum is 55%. All other conditions remain unchanged.

[0063] Test Example 1

[0064] The slurries prepared from the phosphogypsum-based filling materials of Examples 1-4 and Comparative Examples 1-3 were tested.

[0065] (1) Determine the setting time and fluidity of the filling material slurry. The setting time is determined in accordance with the "Test Method for Water Consumption, Setting Time and Stability of Cement Standard Consistency" (GB / T1346-2011); the fluidity test method is basically determined in accordance with the "Test Method for Fluidity of Cement Mortar" (GB / T 2419-2005), and the number of jumps on the jumping table is set to 10 times.

[0066] (2) Compressive strength test

[0067] Take the slurry and pour it into a mold with a size of 70.7×70.7×70.7mm to form it. After gently vibrating the mold 3 times, use a scraper to scrape off the excess slurry on the surface. After standard curing for 24 hours, remove the mold to obtain the test sample. Then put the test sample into an environment with a temperature of 20±3℃ and cure it for 7d and 28d to obtain the filling material sample, and test its compressive strength. The specific steps are: take out the test block that has been cured to the age, set the loading rate to 2.4KN / S, and use an electric pressure testing machine to measure the compressive strength. Take 3 test blocks for each age for testing, and take the average value of the test results as the uniaxial compressive strength value of the filling material at that age.

[0068] The results are shown in the following table:

[0069] Table 2 Performance test results

[0070]

[0071] The data in the table above show that increasing the sulphoaluminate cement content shortens the initial and final setting times, reduces slurry fluidity at the same water-to-cement ratio, and significantly increases both the 7-day and 28-day compressive strengths. This phenomenon demonstrates that in high-sulfate systems, sulphoaluminate cement can effectively accelerate the early hardening of the green body and improve its early strength.

[0072] Comparative experiments show that the setting time of Comparative Example 1 is longer and the compressive strength is lower than that of Example 1, indicating that ordinary Portland cement is not suitable for high sulfate systems. Gypsum will hinder the hydration of Portland cement, but can actively participate in the C4A3S in sulphoaluminate cement. -The hydration reaction of minerals such as sulphoaluminate promotes the formation of ettringite and accelerates the overall hydration process. Therefore, in high-content phosphogypsum-based filling materials, using sulphoaluminate cement instead of ordinary Portland cement can significantly promote the hydration reaction, specifically manifested in shortened setting time, rapid hardening of the green body, and significantly improved early strength.

[0073] To improve the utilization rate of phosphogypsum, its dosage was significantly increased and the amount of cementitious material used was reduced (Comparative Example 2). As a result, the green body had difficulty in setting, delayed demoulding, and extremely low strength, which could not meet the engineering requirements. Therefore, the upper limit of phosphogypsum dosage must be strictly controlled.

[0074] Furthermore, Comparative Example 3 shows that when the hemihydrate gypsum content in the phosphogypsum is too high, the green body expands and cracks severely during the later stages of curing, resulting in a significant decrease in the 28d strength. Therefore, it is important to precisely control the hemihydrate gypsum content in the heat-treated phosphogypsum.

[0075] The above-described embodiments merely represent specific implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of protection of the present application. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the technical concept of the present application, and all such variations and improvements fall within the scope of protection of the present application.

Claims

1. A phosphogypsum-based filling material, characterized in that: The raw materials include the following substances in the following weight ratios: 60-70% of phosphogypsum, 8-20% of fly ash, 2-8% of sulphoaluminate cement and 2-18% of slag powder.

2. A phosphogypsum-based filling material according to claim 1, characterized in that: The raw materials include the following substances in weight ratio: 70% of phosphogypsum, 15% of fly ash, 6% of sulphoaluminate cement and 9% of slag powder.

3. A phosphogypsum-based filling material according to claim 1 or 2, characterized in that: The phosphogypsum is a powdered phosphogypsum obtained by drying and ball-milling the original dihydrate phosphogypsum at 100-110°C.

4. A phosphogypsum-based filling material according to claim 3, characterized in that: The specific surface area of ​​the phosphogypsum is 300-350 kg / m 2 .

5. A phosphogypsum-based filling material according to claim 1 or 2, characterized in that: The total content of SiO2 and Al2O3 in the fly ash is ≥75wt%; The CaO content in the slag powder is ≥40wt%, and the SiO2 content is ≥25wt%; The Al2O3 content in the sulphoaluminate cement clinker is ≥30wt%, and SiO2 is ≤10.5wt%.

6. A method for preparing a phosphogypsum-based filling material according to any one of claims 1 to 5, comprising the following steps: S1. Raw material pretreatment: The original phosphogypsum is subjected to heat treatment and particle size control; the heat treatment comprises drying the phosphogypsum at a constant temperature of 100-105°C for 12-24 hours to obtain phosphogypsum with a mineral phase composition of 80 wt% or more of dihydrate gypsum and 15 wt% or less of hemihydrate gypsum; the particle size control comprises grinding the heat-treated exothermic phosphogypsum in a ball mill to obtain a specific surface area of ​​300-350 m 2 / kg of phosphogypsum powder; preferably, the grinding time is 1 min; S2. Material preparation: Prepare phosphogypsum powder, fly ash, slag powder, and sulphoaluminate cement clinker in proportion; S3. Mix phosphogypsum, fly ash, slag powder and sulphoaluminate cement clinker to obtain the filling material.

7. A phosphogypsum-based filling slurry, characterized in that: The phosphogypsum-based filling material according to any one of claims 1 to 5 is added with water to form a slurry.

8. The phosphogypsum-based filling slurry according to claim 7, characterized in that: The water-to-material ratio of the slurry is 0.55-0.65, preferably 0.6.

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