Road modified phosphogypsum, and preparation method and application thereof

Abstract

The present application relates to solid waste resource utilization technical field, provide a kind of road modified phosphogypsum and its preparation method and application, the road modified phosphogypsum is by the phosphogypsum waste of 15~40% attached water and cement A, with mass ratio 100:1~10 homogenization, aging is obtained.The present application only uses cement as modifier, realizes the harmless treatment of traditional phosphogypsum waste, while, obtains the road modified phosphogypsum of excellent performance, avoids the addition of excessive material and influences its good attribute of green recyclable resource use, simultaneously, avoids the moisture content too large when directly as roadbed material and ecological restoration material, cannot be compacted and formed and the secondary environmental pollution problem generated by the disposal of harmful substance.Furthermore, cement is used as cementing material for the preparation of composite material of the specific road modified phosphogypsum, can realize more excellent physical and mechanical properties under the condition that the utilization rate of phosphogypsum is more than 80%.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of solid waste resource utilization, and particularly relates to a road modified phosphogypsum, a preparation method thereof and application of the road modified phosphogypsum in roadbed fillers, ecological backfill, road base and high-performance ecological restoration materials. BACKGROUND

[0002] Phosphogypsum is the main solid waste discharged in the production of phosphate fertilizer or phosphoric acid. With the rapid development of the phosphorus chemical industry, the cumulative stock of phosphogypsum is huge, which not only occupies a large amount of land, but also contains harmful components such as strong residual acid, soluble fluorine and phosphorus, which can cause serious pollution to soil, water and atmosphere, and constitutes a severe environmental challenge. Therefore, large-scale resource utilization and harmless utilization of phosphogypsum is an urgent need to realize circular economy and sustainable development.

[0003] The application of phosphogypsum in road engineering as a roadbed or base material is one of the effective ways for large-scale utilization. However, due to the production of phosphogypsum by wet-process phosphoric acid process, and the fact that traditional or existing stockyards are mainly stored outdoors, a large amount of attached water exists between the molecules of the phosphogypsum, which causes the phenomenon that the capillary water rises and the soft ball is formed during the compaction operation of the road roller, and the phosphogypsum waste cannot be directly used in the roadbed or base material due to the presence of harmful substances.

[0004] In order to solve the problem of harmful substances, the impurity content is reduced by water washing, flotation and other methods, or lime and other alkaline substances are added to neutralize the residual acidity. Although this can achieve harmless to a certain extent, it generally has the problems of complex process and high treatment cost. More importantly, this process often introduces new chemical substances, which to some extent destroys the essential attribute of green recycling resources. Moreover, on the basis of harmless, the roadbed or base material also needs necessary strength to meet the road standard, and the existing technology usually uses composite cementitious material system for solidification, and most of them integrate the production of harmless and mixture, which causes the concept of resource utilization based on harmless to be confused, and the formed road base still has the risk of environmental pollution of high leaching. For example, a method for preparing a road base material by using phosphogypsum, steel slag, fly ash and cement, which needs the synergistic effect of various industrial solid wastes and cement. The common feature of such technical solutions is the complexity of the cementitious system and the limited amount of phosphogypsum. The complex cementitious system increases the complexity of construction and the uncertainty of quality control, and the amount of phosphogypsum is limited, which limits its large-scale consumption capacity as the main raw material. Moreover, when the amount of phosphogypsum is forcibly increased, the late strength and stability of the material are often difficult to guarantee.

[0005] To address the problem of the large amount of water adhering to gypsum molecules, which prevents its direct application, traditional methods attempt to use air drying. However, due to the highly adhesive nature of its extremely fine molecular aggregates, and the fact that its surface easily loses water and forms a film-like structure under light, the water adhering to gypsum cannot be dried naturally.

[0006] Therefore, existing technologies require complex pretreatment and modification with various cementitious materials to achieve the harmlessness of phosphogypsum and meet road performance requirements. However, this leads to high costs, high energy consumption, and complex processes, contradicting the original intention of low-cost and environmentally friendly solid waste resource utilization. Alternatively, many comprehensive utilization units use a one-time solidification stabilization method to form road base materials for resource utilization. However, this utilization, which does not prioritize harmlessness, even if the result meets strength requirements, deviates from solid waste laws and industry standards. Therefore, there is an urgent need in this field to develop a new technical solution that can achieve a high utilization rate of over 80% of phosphogypsum in road base materials without complex pretreatment, while simultaneously ensuring that the final product has excellent physical and mechanical properties and environmental friendliness. This would truly solve the technical challenge of balancing environmental protection attributes with the premise of harmless disposal of phosphogypsum solid waste for large-scale, high-quality application. Summary of the Invention

[0007] This invention provides a modified phosphogypsum for road use, its preparation method, and its applications, addressing the numerous shortcomings of existing technologies. Specifically, this invention uses only cement as a single modifying material for harmless treatment. After achieving the required standards, it is then used as a raw material in a secondary composite process for road base materials and ecological restoration materials. This stable composite process, using cement as a binder, significantly improves the material's stability, durability, and the reuse efficiency of gypsum-based green, low-carbon, and recyclable materials. Therefore, it meets current regulations and standards while also leveraging the synergistic effect of the mineral activity during the deceleration phase of the hydration reaction in the initial cement-modified material, making its application as a raw material for roadbed filling and ecological backfilling of significant technical importance.

[0008] Specifically, in the first aspect, the present invention provides a modified phosphogypsum for road use, which is obtained by homogenizing and aging granular phosphogypsum waste with an attached water content of 10-45% and cement A at a mass ratio of 100:1-10.

[0009] This invention uses only cement as a modifier to ensure the harmless treatment of phosphogypsum with high adhering water content. The resulting modified phosphogypsum can be used as roadbed filler and for ecological backfilling. In this process, cement is used as a cementing material to recombinate the harmlessly treated modified phosphogypsum into a product that meets the requirements of current regulations and standards. This ensures that the phosphogypsum waste meets the harmless treatment standards and that all indicators meet the requirements of current regulations and standards when used as a raw material in road applications. This achieves the principle of harmless treatment before resource utilization, while also improving the purity of the phosphogypsum used in road applications and avoiding the addition of excessive substances that could affect its good properties as a green and recyclable resource.

[0010] By utilizing the water content in phosphogypsum and the mass ratio of phosphogypsum to cement A, it is possible to achieve an aging time of ≥1 day. This not only reduces the water content in the phosphogypsum but also solidifies the soluble phosphorus, fluorine, other harmful substances, and heavy metals, ensuring that its main indicators meet the requirements of current national standards. Furthermore, it enables homogenized mixing of the powder, fully stimulating its application potential in roadbed fillers and structural base materials under the premise of achieving harmlessness.

[0011] The present invention aims to use cement as a medium and curing agent for the harmless treatment of phosphogypsum. The alkaline properties of cement neutralize the free acid in phosphogypsum, while reducing the water attached to phosphogypsum and realizing the hydration reaction of cement. It also couples and solidifies the harmful substances in phosphogypsum, thereby achieving its harmlessness.

[0012] Specifically, this invention first crushes phosphogypsum waste, then homogenizes the phosphogypsum waste with cement. The homogenization process ensures that the cement and phosphogypsum waste are in full contact, and then the mixture is aged. During the aging process, the time characteristics of the cement hydration reaction are utilized to fully neutralize and passivate the phosphogypsum waste, and the solidification reaction generates insoluble inert salts, thereby forming a harmless modified phosphogypsum raw material for road use. This greatly improves the physical and mechanical properties of road materials while ensuring road safety.

[0013] During the aging process, the water adhering to the phosphogypsum mainly functions as free water, which is used to release the calcium from the cement. 2+ and SO4 2- Ions, dissolved SO4 2- The ions react with C3A (tricalcium aluminate) in cement clinker to form high-sulfur hydrated calcium sulfoaluminate (ettringite, AFt). This product consumes the bound water in phosphogypsum and forms a dense intermolecular layer, delaying cement setting and facilitating the solidification of harmful substances. Furthermore, the gypsum in the system is significantly in excess at this point, making it easier to form a stable ettringite framework. This is beneficial to the mechanical properties of the system, especially when used as a raw material for road base materials. It can form a rich combination of ettringite framework and hydration products with the added cement, which is conducive to the development of the mechanical properties of the base material.

[0014] Meanwhile, during the aging process, the bound water in the phosphogypsum waste further participates in the hydration of silicates, forming hydrated calcium silicate (CSH) gel; at the same time, the phosphate ions in the phosphogypsum catalyze the formation of calcium phosphate gel, strengthening the material structure.

[0015] Due to the aforementioned reactions, when aged modified phosphogypsum is used as a raw material for road base materials, the retarding effect of the phosphogypsum is significantly reduced after the addition of cement, while cement hydration proceeds normally. In other words, for road base materials, the hydration products generated by the cement added during the preparation of modified phosphogypsum synergistically work with the cement added during the preparation of the road base materials to support the mechanical strength of the road base materials.

[0016] According to the modified phosphogypsum for road use provided by the present invention, the average particle size of the phosphogypsum waste is 50~100μm.

[0017] According to the modified phosphogypsum for road use provided by the present invention, the cement contains ≥50% tricalcium silicate (C3S), ≥15% dicalcium silicate, ≥5% tricalcium aluminate, and ≥5% tetracalcium aluminoferrite (C4AF).

[0018] According to the modified phosphogypsum for road use provided by the present invention, the granular phosphogypsum waste is obtained by adjusting the attached water content after crushing the phosphogypsum waste raw material; the mass content of calcium sulfate dihydrate in the phosphogypsum waste raw material is more than 65%, the pH value of the phosphogypsum waste raw material is ≤5, and the harmful substances include: the mass content of soluble phosphorus is more than 0.35%, and / or, the mass content of soluble fluorine is more than 0.45%.

[0019] The granular phosphogypsum waste in this invention is obtained through a single-stage or multi-stage crushing process. Specifically, the single-stage or multi-stage crushing process includes coarse crushing and fine crushing. The coarse crushing process uses a roller crusher or impact crusher to refine the particles to 5-20 mm, breaking up agglomerates and releasing soluble phosphorus and fluorine from the crystals. The fine crushing process uses a high-speed pulverizer or disperser to disperse the undisturbed phosphogypsum to 50-100 μm, controlling 90% of the particles to have a diameter deviation of ≤2 mm. This ensures that the gypsum is fully dispersed, increases the specific surface area, provides a sufficient contact interface for the modification reaction, enhances the reactivity, reduces the impact of harmful impurities, and improves the compatibility of the material.

[0020] According to the modified phosphogypsum for road use provided by the present invention, the homogenization includes: feeding granular phosphogypsum waste into a continuous or multi-stage composite mixing device, forming a three-dimensional turbulent flow field through thorough mixing to ensure that the material is mixed without dead corners; at the same time, cement is continuously added through a metering pump, the mixing time is controlled at 1 to 5 minutes, and the mixing uniformity reaches more than 95%.

[0021] According to the modified phosphogypsum for road use provided by the present invention, the modified phosphogypsum for road use has a pH value ≥6, soluble phosphorus ≤0.3%, soluble fluorine ≤0.2%, attached water content ≤20%, and a maximum particle size of 1.18mm.

[0022] Secondly, the present invention also provides a method for preparing the modified phosphogypsum for road use as described above, wherein phosphogypsum waste with an attached water content of 10-45% is homogenized and aged with cement A at a mass ratio of 100:1-10.

[0023] The method for preparing the modified phosphogypsum for road use provided by the present invention includes: crushing phosphogypsum waste raw material and adjusting its attached water content to 10-45% to obtain unmodified phosphogypsum with a particle size of 5-100 μm.

[0024] Unmodified phosphogypsum and cement A are mixed at a mass ratio of 100:1~10. The mixture is stirred at room temperature at a speed of 100~300 rpm for 5~10 seconds. After stirring, the mixture is aged under natural conditions for 7 days. After aging, modified phosphogypsum for road use is obtained.

[0025] Thirdly, the present invention also provides the application of the modified phosphogypsum for road use as described above in roadbed fillers, ecological backfills, road base materials, and high-performance ecological restoration materials.

[0026] Fourthly, the present invention also provides a composite material comprising: modified phosphogypsum and a cementing material;

[0027] The modified phosphogypsum is selected from the road-grade modified phosphogypsum mentioned above; the cementing material is selected from cement B;

[0028] The mass percentage of the road-grade modified phosphogypsum in the composite material is more than 80%;

[0029] The composite material is a roadbed filler, ecological backfill, road base material, or high-performance ecological restoration material.

[0030] Preferably, the cement B is the same as the cement A.

[0031] According to the composite material provided by the present invention, the maximum density of the composite material is 1.4~1.7 g / cm³. 3 The optimal moisture content is 14-20%.

[0032] Fifthly, the present invention also provides a method for preparing the composite material, comprising: mixing, spreading, rolling and curing modified phosphogypsum and cementitious materials.

[0033] The modified phosphogypsum for road use, its preparation method, and its application provided by this invention use only cement as a modifier. This achieves the harmless treatment of traditional phosphogypsum waste while obtaining high-performance modified phosphogypsum raw materials for road use, avoiding the negative impact of excessive additives on its excellent properties as a green and recyclable resource. Simultaneously, it avoids the problems of excessive moisture content preventing compaction and secondary environmental pollution caused by untreated hazardous substances when directly used as roadbed and ecological restoration materials.

[0034] Furthermore, when cement is used as a binder in the preparation of composite materials with this specific road-grade modified phosphogypsum, even better physical and mechanical properties can be achieved with a phosphogypsum utilization rate of over 80%. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0036] The test indicators and test methods involved in this invention are as follows:

[0037] Appearance: Visual assessment.

[0038] Calcium sulfate dihydrate: Calcium sulfate dihydrate (CaSO4) as specified in GB / T23456 is adopted. . The test was conducted using the 2H2O method.

[0039] Particle size: Tested according to the method specified in GB / T21524, with a sample mass of 500g.

[0040] Adhering water: Determination of adhering water according to GB / T5484 - Drying difference method, drying conditions: drying in a constant temperature drying oven at (40±2)℃.

[0041] pH value: Performed according to the pH value determination method in GB / T5484.

[0042] Soluble phosphorus: Proceed according to the method specified in JC / T2073.

[0043] Soluble fluorine: Performed according to the method specified in JC / T2073.

[0044] 7-day compressive strength: The compressive strength was determined according to the method in GB / T17669.3.

[0045] Where specific techniques or conditions are not specified in the examples, they shall be performed in accordance with the techniques or conditions described in the literature in this field, or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased through legitimate channels.

[0046] The composition of some of the raw materials in this invention is as follows:

[0047] The phosphogypsum waste raw materials used in the embodiments of the present invention are shown in Table 1 below.

[0048] Table 1

[0049]

[0050] The cement used in the embodiments of the present invention is shown in Table 2 below.

[0051] Table 2

[0052]

[0053] Example 1A Road-grade modified phosphogypsum

[0054] This embodiment provides a modified phosphogypsum for road use, the preparation method of which is as follows:

[0055] (1) Pulverize the waste phosphogypsum raw material and adjust its attached water content to 25% to obtain unmodified phosphogypsum with a thickness of 50~100μm.

[0056] (2) Mix unmodified phosphogypsum and cement at a mass ratio of 100:3, stir at room temperature, stir at a speed of 150 rpm for 10 s, and then age under natural conditions for 7 days. After aging, road-use modified phosphogypsum is obtained.

[0057] Example 2A Road-grade modified phosphogypsum

[0058] This embodiment provides a modified phosphogypsum for road use, the preparation method of which is basically the same as that of Example 1A, except that: unmodified phosphogypsum and cement are mixed at a mass ratio of 100:5.

[0059] Example 3A Road-grade modified phosphogypsum

[0060] This embodiment provides a modified phosphogypsum for road use, the preparation method of which is basically the same as that of Example 1A, except that: unmodified phosphogypsum and cement are mixed at a mass ratio of 100:8.

[0061] Example 4A Road-grade modified phosphogypsum

[0062] This embodiment provides a modified phosphogypsum for road use, the preparation method of which is basically the same as that of Example 1A, except that: unmodified phosphogypsum and cement are mixed at a mass ratio of 100:10.

[0063] Example 5A Road-grade modified phosphogypsum

[0064] This embodiment provides a road-use modified phosphogypsum, the preparation method of which is basically the same as that of Example 3A, except that the water content of the adhering material is adjusted to 20% in step (1).

[0065] Example 6A Road-grade modified phosphogypsum

[0066] This embodiment provides a road-use modified phosphogypsum, the preparation method of which is basically the same as that of Example 3A, except that the water content of the adhering material is adjusted to 30% in step (1).

[0067] Example 7A Road-grade modified phosphogypsum

[0068] This embodiment provides a road-use modified phosphogypsum, the preparation method of which is basically the same as that of Example 3A, except that the water content of the adhering material is adjusted to 35% in step (1).

[0069] Example 8A Road-grade modified phosphogypsum

[0070] This embodiment provides a road-use modified phosphogypsum, the preparation method of which is basically the same as that of Example 3A, except that the water content of the adhering material is adjusted to 40% in step (1).

[0071] Example 1B: Road base material

[0072] This embodiment provides a road base material, the preparation method of which is as follows:

[0073] The modified phosphogypsum for road use prepared in Example 1A was mixed with cement at a mass ratio of 100:8 to conduct a standard compaction test, thus obtaining the road base material.

[0074] This invention tests the unconfined compressive strength of the road base material of this invention under the condition of a standard compaction test.

[0075] Examples 2B~8B: Road base materials

[0076] It is basically the same as Example 1B, except that the road-use modified phosphogypsum prepared in Example 1A is replaced by the road-use modified phosphogypsum of Examples 2A to 8A.

[0077] The specific correspondence is shown in Table 3 below:

[0078] Table 3

[0079]

[0080] Comparative Example 1

[0081] This comparative example provides a road base material, the preparation method of which is as follows:

[0082] The unmodified phosphogypsum from Example 1A was mixed with cement at a mass ratio of 100:8 to undergo a standard compaction test to obtain the road base material.

[0083] Test Example 1: Road-use modified phosphogypsum test

[0084] Sample preparation: During the preparation process of Examples 1A to 8A above, samples were taken at different aging time points for testing.

[0085] The test results are shown in Tables 4 and 5 below:

[0086] Table 4

[0087]

[0088] Table 5

[0089]

[0090] Comparing the data from Examples 1A to 8A after aging for 1 day, 3 days, and 7 days, it can be seen that the contents of soluble phosphorus and soluble fluorine both show a significant decreasing trend with the extension of aging time. This proves that the process can effectively treat harmful soluble impurities in phosphogypsum, making it more environmentally friendly and stable.

[0091] From the perspective of appearance and particle size: After aging for 3-7 days, Examples 1A-5A all became "homogeneous, loose powder," and the 1.18mm particle size pass rate reached 100%, indicating that the physical morphology and uniformity of the material were improved. In contrast, Examples 6A-8A had lower particle size pass rates, indicating that their physical modification effect was poor.

[0092] The 7-day compressive strength of Examples 1A to 5A showed a significant increase with aging time. In particular, Examples 3A, 4A, and 5A achieved strengths of 1.1 MPa, 1.0 MPa, and 1.3 MPa on day 7, respectively, far exceeding those of Examples 1A and 2A, and also superior to Examples 6A to 8A. This indicates that controlling the adsorbed water content using the method of this invention plays a crucial role in improving the early strength of the modified phosphogypsum.

[0093] In summary, this invention uses only cement as a modifier to achieve the harmless treatment of traditional phosphogypsum waste while obtaining high-performance modified phosphogypsum for road use, avoiding the addition of excessive substances that would affect its good properties as a green and recyclable resource.

[0094] Test Example 2: Road Base Material Testing

[0095] Sample preparation: During the preparation process of Examples 1B to 8B above, the samples obtained at the end of the standard compaction test were tested.

[0096] The test indicators and their test methods are as follows: The optimal moisture content and maximum density test methods are carried out in accordance with the "Test Procedure for Inorganic Binder Stabilized Materials in Highway Engineering" JTG3441.

[0097] Unconfined strength: The material was stored under curing conditions of (20±2)°C and ≥95% humidity, and samples were taken at different time points for testing. The testing method was carried out in accordance with the "Test Procedure for Inorganic Binder Stabilized Materials in Highway Engineering" JTG3441.

[0098] The test results are shown in Tables 6 and 7 below:

[0099] Table 6

[0100]

[0101] Table 7

[0102]

[0103] As can be seen from the table above, except for Example 8B, the maximum density of the other examples is higher than that of Comparative Example 1. Higher density generally means stronger load-bearing capacity and stability.

[0104] At all curing periods (3d, 7d, 14d, 28d), the strength of all embodiments was several times that of Comparative Example 1. For example, at the critical 7-day curing period, the strength of Embodiments 1B-5B (2.0-2.8 MPa) was 2.5 to 3.5 times that of Comparative Example 1 (0.8 MPa); at the 28-day curing period, the strength of the embodiments (4.0-5.3 MPa) was 2.3 to 3.1 times that of Comparative Example 1 (1.7 MPa). This indicates that the present invention can significantly improve the mechanical properties and load-bearing capacity of the final product. However, combined with the data from Embodiments 6B-8B, it can be seen that the attached water content plays a key role in regulating the physical properties of the road base material in the present invention. The method of the present invention avoids the problems of excessive water content, secondary environmental pollution caused by untreated harmful substances, and poor physical properties when directly used as roadbed material and ecological restoration material.

[0105] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; 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 of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A composite material, characterized in that, include: Modified phosphogypsum and cementitious materials for road use; the maximum density of the composite material is 1.4~1.7 g / cm³. 3 The optimal moisture content is 14-20%. Granular phosphogypsum waste with an attached water content of 20-45% is mixed with cement A at a mass ratio of 100:1-10, and stirred for 5-10 seconds. After stirring, it is aged under natural conditions. After aging, a road-grade modified phosphogypsum with a maximum particle size of 1.18 mm is obtained. The road-grade modified phosphogypsum has a pH value ≥6, soluble phosphorus ≤0.3%, soluble fluorine ≤0.2%, and attached water content ≤20%. The cementitious material is selected from cement B; The mass percentage of the road-grade modified phosphogypsum in the composite material is more than 80%.

2. The composite material according to claim 1, characterized in that, The average particle size of the phosphogypsum waste is 50~100μm.

3. The composite material according to claim 1, characterized in that, The cement A contains ≥50% tricalcium silicate, ≥15% dicalcium silicate, ≥5% tricalcium aluminate, and ≥5% tetracalcium aluminoferrite.

4. The composite material according to claim 1, characterized in that, The granular phosphogypsum waste is obtained by pulverizing phosphogypsum waste raw materials and adjusting the attached water content; the phosphogypsum waste raw materials contain more than 65% calcium sulfate dihydrate by mass, the pH value of the phosphogypsum waste raw materials is ≤5, and the harmful substances include: more than 0.35% soluble phosphorus by mass, and / or more than 0.45% soluble fluorine by mass.

5. A method for preparing the composite material according to any one of claims 1 to 4, characterized in that, include: The modified phosphogypsum is obtained by mixing, spreading, rolling, and curing with cementitious materials.

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