A preparation method of phosphogypsum aggregate, its product and its application in road water-stabilizing layer

Abstract

The present invention discloses a method for preparing phosphogypsum aggregate, its product and its application in the water-stabilizing layer of roads, which belongs to the field of highway construction materials and includes the following steps: drying and treating phosphogypsum, weighing, pressing into blocks, mechanical crushing, screening, and carrying out in a high-humidity environment. The present application does not require the use of sintering to prepare aggregates, and can effectively simplify the aggregate preparation process. Based on the prepared phosphogypsum aggregate, the inventor uses it in road construction, which can be used to replace the crushed stone of the water-stabilizing layer, and can also be used as a roadbed filler and a modified fly ash stabilized road base material. The present application uses phosphogypsum aggregate as a highway base material, which has a wide source of raw materials and a huge demand for road construction, and has broad application prospects. The use of this application can effectively reduce the cost of road construction and realize the resource utilization of phosphogypsum, which is of great significance for protecting the environment, reducing environmental pollution and achieving sustainable development.

Description

Technical Field

[0001] This application relates to the field of highway transportation, particularly highway construction materials, and specifically to a method for preparing phosphogypsum aggregate, its product, and its application in road water-stabilizing layers. Using phosphogypsum as the primary raw material, this application successfully prepares high-strength phosphogypsum aggregate, which is then used in road water-stabilizing layers. This helps reduce phosphogypsum accumulation and lowers road construction costs, possessing significant economic and social value. Background Art

[0002] Currently, my country's expressway mileage far surpasses any other country, ranking first in the world. According to the National Highway Network Plan, highway construction (including expressways) will remain a key component of my country's infrastructure over the next decade. Road construction requires large quantities of crushed stone, currently obtained primarily through mountain quarrying and river collection. As a non-renewable resource, large-scale collection of natural crushed stone will inevitably impact the ecological environment and is not in line with my country's sustainable development strategy. To meet the needs of highway construction and minimize environmental damage, it is necessary to find new recycled aggregates to replace the crushed stone required for road construction.

[0003] On the other hand, phosphogypsum, an industrial byproduct, is currently primarily disposed of in open-air dumps due to its high production volume. This method not only requires significant land, but also poses the risk of long-term storage, potentially polluting groundwater, soil, and air, damaging the ecological environment and hindering the sustainable development of the phosphorus chemical industry.

[0004] Extensive research has been conducted both domestically and internationally to address the challenges of phosphogypsum treatment. Currently, existing phosphogypsum treatment processes still face the following challenges: (1) high costs for harmless phosphogypsum treatment; and (2) low phosphogypsum content in phosphogypsum products. Reducing phosphogypsum treatment costs and developing high-value-added phosphogypsum products with high phosphogypsum content are key to resolving the challenges of phosphogypsum resource utilization.

[0005] Based on the characteristics of phosphogypsum, some studies have been conducted on its use in road construction. Studies from the University of Florida and the University of Miami in the United States have shown that the mixture made by adding a certain amount of clay sand to phosphogypsum is an excellent roadbed filler. Research from Southwest Jiaotong University has shown that the comprehensive performance of the roadbed made of phosphogypsum-modified soil filler meets the indicators of a secondary highway and has no obvious dynamic fatigue characteristics. Wuhan University of Technology has confirmed through experiments that the mechanical properties of phosphogypsum-modified fly ash materials are generally enhanced at all times. Experiments conducted by Southeast University have shown that a reasonable amount of phosphogypsum can replace part of the raw materials of the original fly ash crushed stone to a certain extent, and can effectively save highway construction costs while ensuring the road performance of the mixture.

[0006] One type of road base layer uses a cement-stabilized graded gravel base layer, referred to as a water-stable layer. This layer uses graded gravel as the aggregate, uses a certain amount of gel material and a sufficient volume of mortar to fill the gaps between the aggregates, and is spread and compacted according to the principle of interlocking. The inventors discovered that the amount of graded gravel required for the water-stable layer is extremely large. If products prepared from phosphogypsum could be used to replace the gravel in the existing water-stable layer, it would not only solve the problem of road construction consuming a large amount of gravel and affecting the ecological environment, but also realize the resource utilization of phosphogypsum, which is of great significance and value. To this end, the inventors conducted in-depth research and ultimately obtained the technical solution of the present application. Summary of the Invention

[0007] The purpose of the present invention is to provide a method for preparing phosphogypsum aggregate, its product and its application in the water-stabilizing layer of roads in response to the above-mentioned problems. This application uses phosphogypsum as the main raw material, blast furnace slag powder and cement as composite gel materials, supplemented by an alkaline activator mainly composed of calcium oxide, and successfully prepares high-strength phosphogypsum aggregate by controlling the components of the alkaline activator. This application does not require the use of sintering to prepare aggregates, and can effectively simplify the aggregate preparation process. Based on the prepared phosphogypsum aggregate, the inventor uses it in road construction, which can be used to replace the crushed stone of the water-stabilizing layer, and can also be used as a roadbed filler and a modified fly ash stabilized road base material. This application uses phosphogypsum aggregate as a highway base material, which has a wide source of raw materials and a huge demand for road construction, and has broad application prospects. The use of this application can effectively reduce the cost of road construction and realize the resource utilization of phosphogypsum, which is of great significance for protecting the environment, reducing environmental pollution and achieving sustainable development.

[0008] In order to achieve the above object, the present invention adopts the following technical solutions:

[0009] A method for preparing phosphogypsum aggregate comprises the following steps:

[0010] (1) drying the phosphogypsum to obtain dried phosphogypsum;

[0011] (2) Weighing the powders of each component according to the ratio, mixing and stirring the weighed powders of each component to form a first intermediate;

[0012] (3) The prepared first intermediate is placed in a mold of a pressure gauge and pressed to compact the mixture into a block, which is recorded as the second intermediate;

[0013] (4) Mechanically crushing the second intermediate obtained in step 3 to form a coarse aggregate, which is recorded as the third intermediate;

[0014] (5) Sieving the third intermediate to obtain aggregate blanks of different particle sizes;

[0015] (6) curing the aggregate obtained in step 5 at room temperature and a humidity ≥ 70%; after the curing is completed, phosphogypsum aggregate is obtained;

[0016] In step 2, the mass percentages of the components are as follows: 55-65 wt% phosphogypsum, 20-30 wt% slag powder, 8-10 wt% molding cement, 0.5-1.5 wt% calcium oxide, 1.5-2.5 wt% ammonium sulfate, 1.5-2.5 wt% sodium silicate, and 1-3 wt% cationic starch.

[0017] In the step 1, the water content of the dried phosphogypsum is ≤5wt%.

[0018] The mass ratio of the ammonium sulfate to the sodium silicate is 1:0.9-1.2.

[0019] The molding cement is PO42.5.

[0020] In step 6, the room temperature is 5-40° C., and the curing time is 1-10 days.

[0021] The product prepared by the above-mentioned method for preparing phosphogypsum aggregate.

[0022] The application of the aforementioned phosphogypsum aggregate in road water-stabilizing layers.

[0023] It includes phosphogypsum aggregate with a particle size of 9.5 to 19 mm and phosphogypsum aggregate with a particle size of 4.75 to 9.5 mm.

[0024] Phosphogypsum aggregate with a particle size of 9.5 to 19 mm was recorded as coarse aggregate, and phosphogypsum aggregate with a particle size of 4.75 to 9.5 mm was recorded as fine aggregate;

[0025] In the warm water layer of the road, the mass ratio of fine aggregate to coarse aggregate is 1:2~5.

[0026] In response to the aforementioned problems, the present application provides a preparation method, product, and application of phosphogypsum-based concrete solid bricks. In the present application, phosphogypsum aggregate is prepared using raw materials including the following components: phosphogypsum, slag powder, molding cement, calcium oxide, ammonium sulfate, sodium silicate, and cationic starch. Among them, phosphogypsum is used as the main raw material, blast furnace slag powder and cement are used as composite gel materials (blast furnace slag powder is based on steel slag and is a secondary recycled waste product), supplemented with an alkaline activator mainly composed of calcium oxide. By controlling the components of the alkaline activator, high-strength phosphogypsum aggregate is successfully prepared.

[0027] Under normal conditions, slag powder contains a large amount of glass. When it comes into contact with water, the weakest Ca-O bond in the glass breaks. The alkaline activator increases the pH value of the solution, accelerating the dissociation of Si-O and Al-O structures in the glass, generating silicate ions and aluminate ions, which react with the Ca-O bond released by the slag hydrolysis. 2+ The reaction produces calcium silicate hydrate and tricalcium aluminate; tricalcium aluminate reacts with gypsum to form hydraulic ettringite. Furthermore, slag hydration produces calcium silicate hydrate gel (CSH gel). A small amount of hydraulic ettringite can fill pores and reduce system shrinkage, with little effect on strength. However, excessive alkali activator will produce more hydraulic ettringite, causing the system to expand and generate greater internal stress. Consequently, strength decreases with increasing alkali activator content. Over time, the ettringite structure is destroyed by water evaporation, resulting in a decrease in strength.

[0028] In the present application, a method of controlling the amount of calcium oxide added and doping with partial cationic starch is adopted. When preparing phosphogypsum aggregate, the various components are evenly mixed together, and the cationic starch uniformly coats the phosphogypsum. When prepared into aggregate blanks and cured in a high-humidity environment, the phosphogypsum dissolves sulfate anions in water, which will adsorb to the cationic starch in the coating layer, thereby preventing the sulfate ions from hydrating with cement to form calcium aluminate. It should be noted that the present application does not use an external heat source to gelatinize the cationic starch, but gelatinizes the cationic starch based on the heat generated by the pyrolysis of calcium oxide in a high-humidity environment. Using this method, not only can the heat consumption required for heating and gelatinization be reduced, but also after gelatinization, mixing will cause the uniformity of the material to deteriorate, making the overall strength of the prepared phosphogypsum aggregate unstable. Based on the improved method, the problem of uneven mixing of phosphogypsum aggregate raw materials is solved, energy consumption is reduced, and it is gelatinized after obtaining the aggregate blank, so the prepared phosphogypsum aggregate has higher strength and is more stable. At the same time, the present application is doped with part of ammonium sulfate and sodium silicate; on the one hand, ammonium sulfate, sodium silicate and calcium oxide jointly act as stimulators; on the other hand, the test results show that there is an obvious synergistic effect between ammonium sulfate, sodium silicate, calcium oxide and components such as phosphogypsum and slag powder, which can effectively solidify calcium ions, inhibit the further dissolution of phosphogypsum in water, and improve the strength of phosphogypsum aggregate.

[0029] Based on this improved solution, the phosphogypsum content in the phosphogypsum aggregate of this application is greater than 40%, and the compressive strength of the phosphogypsum aggregate is greater than that of sedimentary rock (no less than 30 MPa). Furthermore, this application successfully avoids the purification process of phosphogypsum, preventing environmental pollution caused by harmful components in phosphogypsum. This high phosphogypsum utilization rate opens up a new path for the comprehensive utilization of phosphogypsum by phosphogypsum-emitting enterprises.

[0030] The prepared phosphogypsum aggregate was tested using the "n" method of maximum density theory to calculate the particle size distribution of the aggregate gradation, following the dense gradation recommended in the "Testing Procedures for Highway Engineering Aggregates" (JTG E42-2005). By controlling the proportion of coarse particles, different aggregate gradations were designed. Test results show that the phosphogypsum aggregate prepared using this application meets the strength requirements for water-stabilized layers of highways of Grade II and below, as specified in the "Design Specifications for Asphalt Pavements of Highways" (JTG D50-2017).

[0031] Due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0032] (1) In this application, the raw materials used to prepare the phosphogypsum aggregate are cheap and sintering is not required, so the manufacturing cost of the phosphogypsum aggregate is low; at the same time, the large-scale application of phosphogypsum (phosphogypsum content > 40%) can not only reduce the waste disposal cost of the phosphorus chemical industry, but also increase the added value of the phosphorus chemical industry, and has broad market prospects;

[0033] (2) The adoption of this application can effectively solve the problem of resource utilization of phosphogypsum, open up a new way for resource utilization of phosphogypsum, and comply with the requirements of circular economy and resource conservation and comprehensive utilization;

[0034] (3) The phosphogypsum aggregate of the present application can be used not only for the preparation of concrete solid bricks, but also for the preparation of the water-stabilizing layer of the highway in the present application, thereby reducing the mining and use of natural gravel, effectively reducing the damage to the environment caused by gravel mining, and meeting the strength requirements of the water-stabilizing layer of secondary and lower highways, which is conducive to reducing the cost of highway construction, increasing the added value of phosphorus chemical enterprises, improving the corresponding economic benefits, and promoting the healthy development of the phosphorus chemical industry. DETAILED DESCRIPTION

[0035] All features disclosed in this specification, or all steps in the disclosed methods or processes, except mutually exclusive features and / or steps, can be combined in any manner.

[0036] Any feature disclosed in this specification, unless otherwise stated, may be replaced by other equivalent or similar features. That is, unless otherwise stated, each feature is only an example of a series of equivalent or similar features.

[0037] In the examples of this application, phosphogypsum (PG) was purchased from a location in Sichuan and is a gray powder whose main component is CaSO4·2H2O. 42.5% ordinary Portland cement was purchased from a location in Sichuan; sodium silicate pentahydrate (AR), ammonium sulfate (AR), and quicklime (AR) were purchased from a company in Tianjin. Blast furnace slag powder is a commercially available product, and its activity index test method complies with the national standard GB / T18046-2008. The product characteristics are: specific surface area 480-580 m2 / kg, physical appearance is spherical; activity index 3d ≥ 90%, 7d ≥ 100%, 28d ≥ 110%; fluidity ratio ≥ 100%, water content (mass fraction) ≤ 1.0%, sulfur trioxide (mass fraction) ≤ 4.0%, chloride ion (mass fraction) ≤ 0.06%, loss on ignition (mass fraction) ≤ 3.0%.

[0038] PG and PO42.5 cements were tested respectively, and their chemical compositions are shown in Table 1 below.

[0039] Table 1 Chemical composition

[0040]

[0041] Note: In Table 1, R2O represents an alkali metal oxide.

[0042] In this example, the phosphogypsum sample used was in a gray powder form and had already been dried, so the corresponding drying step was omitted. In this example, the curing temperature was 20-25°C. For ease of comparison, the curing time in all examples was 2 days, and the humidity in the curing chamber was 80-90%. After curing, the compressive strength of the prepared phosphogypsum aggregate was tested at 3 days, 7 days, and 28 days.

[0043] The process of preparing phosphogypsum aggregate in the embodiment of the present application is as follows (wherein, the mass percentage of each component in the phosphogypsum aggregate is shown in Table 2 below).

[0044] (1) Weigh the raw materials

[0045] Weigh each component according to the ratio, mix and stir the weighed components to obtain a first intermediate.

[0046] (2) Pressing

[0047] The prepared first intermediate is placed in a mold of a pressure gauge for pressing, and the mixture is compacted into a block, which is recorded as the second intermediate.

[0048] (3) Broken

[0049] The obtained second intermediate is mechanically crushed to form a coarse aggregate, which is recorded as the third intermediate.

[0050] (4) Screening

[0051] The obtained third intermediate is sieved to obtain aggregate blanks with different particle sizes.

[0052] (5) Maintenance

[0053] The aggregate blank is cured in a curing box at room temperature and a humidity of 80-90%. After the curing is completed, phosphogypsum aggregate is obtained.

[0054] Table 2 Group distribution ratios in various embodiments

[0055]

[0056] The properties of the phosphogypsum aggregates prepared in Examples 1 to 10 above were tested, and the results are shown in Table 3.

[0057] Table 3 Compressive strength test results of phosphogypsum aggregate

[0058]

[0059] Example 11

[0060] The phosphogypsum aggregate prepared in Example 10 was used as raw material, the phosphogypsum aggregate with a particle size of 0.475 to 9.5 mm was used as fine aggregate, and the phosphogypsum aggregate with a particle size of 9.5 to 19 mm was used as coarse aggregate.

[0061] After fine aggregate and coarse aggregate are graded in a ratio of 1:4, they are added into a mixer and mixed thoroughly to make graded crushed stone.

[0062] Weigh the components according to the following weight ratio: 4 parts of PO325 cement, 10 parts of fly ash, and 86 parts of graded crushed stone; make the weighed components into a highway water-stabilizing layer and carry out maintenance. After the maintenance is completed, it is ready.

[0063] The highway water-stabilizing layer prepared in this embodiment was measured, and its 7d unconfined compressive strength was 4.7 MPa, and its 28d unconfined compressive strength was 16.9 MPa.

[0064] The above test results show that this application successfully prepared a corresponding highway water-stabilizing layer by grading phosphogypsum aggregates of different particle sizes, which can meet the strength requirements of water-stabilizing layers for second-level highways and below. At the same time, this application uses phosphogypsum as the main raw material, which accounts for a high proportion of the aggregate in the water-stabilizing layer, realizing the resource utilization of phosphogypsum, which is conducive to reducing road construction costs, has high economic and social value, and broad application prospects.

[0065] The above description is only a few examples of the present application, which are only used to illustrate the technical solutions of the present invention and are not intended to limit them. The present invention extends to any new features or any new combination disclosed in this specification, as well as any new method or process steps or any new combination disclosed.

Claims

1. A method for preparing phosphogypsum aggregate, characterized in that: The steps include: (1) drying the phosphogypsum to obtain dried phosphogypsum; (2) Weighing the powders of each component according to the ratio, mixing and stirring the weighed powders of each component to form a first intermediate; (3) The prepared first intermediate is placed in a mold of a pressure gauge and pressed to compact the mixture into a block, which is recorded as the second intermediate; (4) Mechanically crushing the second intermediate obtained in step (3) to form a coarse aggregate, which is recorded as the third intermediate; (5) Screening the third intermediate to obtain aggregate blanks of different particle sizes; (6) curing the aggregate blank obtained in step (5) at room temperature and humidity ≥ 70%; after the curing is completed, phosphogypsum aggregate is obtained; In step (2), the mass percentages of the components are as follows: 55-65 wt% phosphogypsum, 20-30 wt% slag powder, 8-10 wt% molding cement, 0.5-1.5 wt% calcium oxide, 1.5-2.5 wt% ammonium sulfate, 1.5-2.5 wt% sodium silicate, and 1-3 wt% cationic starch.

2. The method for preparing phosphogypsum aggregate according to claim 1, wherein: In the step (1), the water content of the dried phosphogypsum is ≤5wt%.

3. The method for preparing phosphogypsum aggregate according to claim 1, characterized in that: The mass ratio of the ammonium sulfate to the sodium silicate is 1:0.9-1.

2.

4. The method for preparing phosphogypsum aggregate according to any one of claims 1 to 3, characterized in that: The molding cement is PO42.

5.

5. The method for preparing phosphogypsum aggregate according to any one of claims 1 to 3, characterized in that: In the step (6), the room temperature is 5-40°C, and the curing time is 1d-10d.

6. Phosphogypsum aggregate prepared by the method for preparing phosphogypsum aggregate according to any one of claims 1 to 5.

7. Use of the phosphogypsum aggregate according to claim 6 in a road water-stabilizing layer.

8. The use according to claim 7, characterized in that It includes phosphogypsum aggregate with a particle size of 9.5 to 19 mm and phosphogypsum aggregate with a particle size of 4.75 to 9.5 mm.

9. The use according to claim 7, characterized in that Phosphogypsum aggregate with a particle size of 9.5 to 19 mm was recorded as coarse aggregate, and phosphogypsum aggregate with a particle size of 4.75 to 9.5 mm was recorded as fine aggregate; In the road water-stabilizing layer, the mass ratio of fine aggregate to coarse aggregate is 1:2~5.

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