A semi-rigid aggregate type geotechnical filler and its preparation process

Abstract

The present invention discloses a semi-rigid agglomerated type geotechnical filler and its preparation process. 1) Put phosphogypsum into a drum granulator, pour in a certain proportion of cement-bentonite mixed material for the first feeding, and stir evenly. 2) Uniformly inject water into the stirred mixed material to form a phosphogypsum agglomerated intermediate. 3) Uniformly sprinkle the uniformly mixed cement-bentonite mixed material on the surface of the rolling agglomerated intermediate for the second feeding, and continue to roll and form to obtain a phosphogypsum double-layer closed structural agglomerate. 4) Naturally cure the obtained phosphogypsum agglomerate to obtain the finished product for use as a geotechnical filler. The present invention belongs to a method for the resource utilization of phosphogypsum. Its two-feeding process can convert phosphogypsum into a semi-rigid double-layer closed structural agglomerate, which can effectively solidify harmful substances in the agglomerate. The finished product has no dust, is resistant to leaching, has high strength, good water resistance, and excellent gradation, and is an excellent geotechnical filler.

Description

Technical Field

[0001] The present invention relates to the field of resource utilization of solid waste, and particularly to a semi-rigid agglomerated soil geotextile filler and a preparation process thereof. Background Art

[0002] Phosphogypsum (PG) is a solid industrial waste discharged during the production of phosphoric acid by the wet process in phosphate chemical enterprises. Its main chemical component is CaSO4·2H2O. It is calculated that about 4.5 - 5.5t of phosphogypsum is produced for every 1t of phosphoric acid produced, and the physical quantity is about 7t. The phosphogypsum discharged by phosphate fertilizer chemical enterprises every year exceeds 10 million tons, and the cumulative discharge is nearly 100 million tons. In addition to CaSO4, phosphogypsum also contains undecomposed phosphate rock, unwashed phosphoric acid, calcium fluoride, iron and aluminum compounds, acid-insoluble substances, organic matter and other impurities, which affect the utilization of phosphogypsum.

[0003] Traditionally, phosphogypsum is regarded as waste and is often disposed of by stacking or landfilling. This disposal method not only causes waste of land resources, but also poses serious environmental risks during rainfall and long-term stacking. Heavy metals and radioactive elements in untreated phosphogypsum may leak into the soil and groundwater through the leaching action of rainfall, posing a potential threat to the ecosystem and human health; during mechanical operations in phosphogypsum yards and in dry and windy weather, dust will be generated, causing dust pollution and having a negative impact on the air quality in the surrounding areas, seriously threatening the health of nearby residents and causing chronic diseases such as cough, asthma, and bronchitis; harmful impurities such as phosphorus, mercury, cadmium, and radioactive elements in phosphogypsum will enter the atmosphere with steam, which will also harm the atmospheric environment; phosphogypsum reservoirs usually have a high potential energy. Once a dam break occurs and causes a debris flow, it will not only cause serious ecological problems, but also seriously threaten the lives and property safety of surrounding residents.

[0004] Due to the characteristics of large number of construction sites, long lines, and wide areas in China's urban construction, a large amount of raw materials are required. As a potential raw material for base construction, phosphogypsum can not only solve various problems caused by the large stockpiling of phosphogypsum, but also solve the problem of the large demand for raw materials due to rapid development. In aspects such as urban construction, transportation infrastructure, water conservancy projects, and environmental governance, geotechnical fillers, as an important engineering material, play an irreplaceable role. Existing research shows that phosphogypsum has fine particles required for base materials and calcium sulfate dihydrate required for the hydration and hardening of cementitious materials, and can completely play the role of aggregate filling and cementitious solidification, thereby improving the volume stability of base materials and reducing pollutant release. If phosphogypsum can be widely used as an excellent geotechnical filler, it can bring good economic benefits while promoting the sustainable development of infrastructure construction. Research shows that by utilizing the micro-expansion characteristics of phosphogypsum, the problem of easy shrinkage and cracking of ordinary semi-rigid bases can be effectively improved, and it has a certain early strength enhancement effect. However, the method of fixing phosphogypsum has problems such as poor stabilization effect and high leaching concentration of heavy metal elements, making it difficult to be directly used in infrastructure construction. Therefore, it is particularly important to develop a method that can simply and effectively process a large amount of phosphogypsum into high-quality geotechnical fillers for direct application in engineering construction. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a semi-rigid agglomerated geotechnical filler and its preparation process, which uses the method of agglomerating phosphogypsum to dispose of the solid waste phosphogypsum, solidifies and encapsulates harmful substances in the agglomerate coating layer, effectively reduces the permeability of harmful substances, and finally realizes the stabilization, harmlessness and resource utilization of phosphogypsum, and can be made into a geotechnical filler with excellent gradation and performance for direct use in infrastructure construction.

[0006] To solve the above technical problems, the present invention provides a semi-rigid agglomerated geotechnical filler and its preparation process, including the following steps:

[0007] S1: Pour the dry cement and bentonite mixed material into a drum granulator filled with crushed phosphogypsum according to a ratio and stir evenly;

[0008] S2: Roll and granulate the obtained mixed material in a drum granulator, and gradually inject water evenly into the mixed material with a sprayer while rolling. After shaping, a spherical phosphogypsum agglomeration intermediate is made;

[0009] S3: Evenly sprinkle cement and bentonite on the surface of the phosphogypsum agglomeration intermediate in the drum granulator for secondary feeding, and continue to roll and granulate to finally obtain a phosphogypsum double-layer closed-structured agglomerate with a diameter of 0.25 - 10 mm;

[0010] S4: Stack and cure the phosphogypsum aggregates under dry and shady natural conditions for 28 days to obtain finished products with a certain strength.

[0011] Further, the mass percentages of the raw materials in the materials described in step S1 are based on the mass of phosphogypsum, which are respectively: cement: 3 - 5%, bentonite: 5 - 9%.

[0012] Further, the phosphogypsum in the materials described in step S1 needs to be preliminarily crushed for large lumps and evenly stirred with the dried cement - bentonite mixture to improve its fluidity and dispersibility.

[0013] Further, in step S1, phosphogypsum, cement, and bentonite need to be fully mixed and stirred evenly by a drum granulator. The inclination angle of the granulator is 45° - 55°, the rotation speed during stirring is 70 - 85 r / min, and the stirring duration is 10 - 15 min.

[0014] Further, in step S2, one - time water injection needs to be completed during the rolling of the mixed materials. The water injection is carried out in the form of fog - like or column - like water spraying, and the water addition speed shall not be greater than 1.25 mL / min, so that the mixed materials are evenly wetted to improve the agglomeration rate and ensure uniform particle size.

[0015] Further, in step S2, the inclination angle of the granulator is 30° - 45°, the rotation speed of rolling granulation is 70 - 85 r / min, and the rolling duration is 10 - 15 min.

[0016] According to the preparation process described in claim 1, characterized in that in step S3, the second - time mixed materials need to be added when the first - time rolling granulation is basically agglomerated and stable, so that the aggregates are completely wrapped by the cement - bentonite hard - shell system.

[0017] Further, the mass percentages of the raw materials in the materials described in step S3 are based on the mass of phosphogypsum, which are respectively: cement: 2 - 3%, bentonite: 5%.

[0018] Further, in step S3, the rotation speed of rolling granulation is 70 - 85 r / min, and the rolling duration should not exceed 20 min.

[0019] Further, in step S4, the phosphogypsum - based aggregates should be cured in a dry and shady place. During natural curing, there is no need to turn the pile, and direct contact with rainwater should be avoided. After curing, its compressive strength is 1 - 10 MPa.

[0020] The present invention also discloses a semi - rigid agglomerated geotechnical filler prepared according to any of the above - mentioned preparation processes.

[0021] Compared with the prior art, the beneficial effects of the present invention are:

[0022] 1. The raw materials required for the present invention are phosphogypsum, cement, bentonite and water, among which phosphogypsum accounts for more than 70%. Except for phosphogypsum, the dosages of other additives are small and easy to obtain, greatly reducing the economic cost of the resource utilization of phosphogypsum.

[0023] 2. The present invention proposes to use a drum granulator for the agglomeration treatment of phosphogypsum. The required equipment is mature and the implementation process is simple, facilitating the realization of the production line processing technology in the workshop environment.

[0024] 3. In the method for the agglomeration treatment of phosphogypsum proposed by the present invention, by adding a certain proportion of cement and bentonite to phosphogypsum, heavy metal elements such as Pb, Cd, Hg, and Cr in phosphogypsum are effectively fixed. The strength of the double-layer closed-structured agglomerates of phosphogypsum obtained by the secondary addition process can reach 10 MPa, with strong water stability and an agglomeration rate of more than 85%.

[0025] 4. The double-layer closed-structured agglomerates of phosphogypsum prepared by the present invention are semi-rigid. This property can increase the stability of the agglomerates to maintain the structural integrity, reduce the shedding or dispersion of particles; can increase the compressive performance of the agglomerates, enabling them to withstand greater pressure or load and improving the durability of the material; can improve the fluidity of the agglomerates, maintaining a certain stiffness and shape for easy processing or transportation.

[0026] The solid waste phosphogypsum in the above method mainly refers to the solid waste generated by phosphochemical enterprises during the wet production of phosphoric acid; the bentonite used is calcium-based bentonite with Ca 2+ as the interlayer cation; the cement used is P.O42.5 Portland cement. The present invention utilizes the bonding effect of the hydration products C-S-H gel and ettringite of phosphogypsum and cement and bentonite to form agglomerates with phosphogypsum as the skeleton, and through the above two addition methods, a structural layer with a certain strength is formed on the outside of the agglomerates, not only reducing the bonding between agglomerates but also having a greater agglomerate strength. The prepared agglomerates have no dust emission, are resistant to leaching, have high strength and good water resistance.

[0027] In summary, the present invention realizes the large-scale disposal of solid waste phosphogypsum, solidifies and contains harmful substances in the agglomerate coating layer, effectively reduces the permeability of harmful substances, and at the same time, the double-layer closed structure formed by the two feeding processes greatly improves the strength of the agglomerates, has no dust emission, is resistant to leaching, and finally realizes the stabilization, harmlessness and resource utilization of phosphogypsum, and can be made into geotechnical fillers with excellent performance and directly used in infrastructure construction, with the advantages of simple process, small pollution and turning waste into treasure. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is the process flow chart of the present invention.

[0029] Figure 2 It is a schematic diagram of a double-layer closed-structured aggregate of phosphogypsum. Specific implementation manners

[0030] The present invention will be further described below in conjunction with the accompanying drawings, but the protection scope of the present invention is not limited to the content described.

[0031] For clarity, not all features of the actual embodiments are described. In the following description, well-known functions and structures are not described in detail because they would clutter the present invention with unnecessary details. It should be considered that in the development of any actual embodiment, a large number of implementation details must be made to achieve the specific goals of the developer, for example, changing from one embodiment to another according to the relevant system or business restrictions. Additionally, it should be considered that such development work may be complex and time-consuming, but it is only routine work for those skilled in the art.

[0032] A semi-rigid aggregate type geotechnical filler and its preparation process include the following steps:

[0033] S1: Pour phosphogypsum, cement, and bentonite into a drum granulator in proportion and stir evenly to form a mixed material. The mass percentages of the respective raw materials in the material are based on the mass of phosphogypsum, which are respectively: cement: 3 - 5%, bentonite: 5 - 9%. The inclination angle of the granulator is 45° - 55°, the rotation speed during stirring is 70 - 85 r / min, and the stirring duration is 10 - 15 min.

[0034] S2: Granulate the obtained mixed material in the drum granulator, and gradually and evenly inject water into the mixed material while rolling. After shaping, a spherical phosphogypsum aggregate intermediate is formed. It is necessary to complete the one-time water injection during the rolling of the mixed material. The water injection is carried out in the form of fog or columnar water spraying, and the water addition speed shall not be greater than 1.25 mL / min. The inclination angle of the granulator is 30° - 45°, the rotation speed of rolling granulation is 70 - 85 r / min, and the rolling duration is 10 - 15 min.

[0035] S3: Evenly sprinkle cement and bentonite on the phosphogypsum aggregate intermediate in the drum granulator and continue rolling granulation to finally obtain a phosphogypsum double-layer closed-structured aggregate with a diameter of 0.25 - 10 mm. The mass percentages of the respective raw materials in the material are based on the mass of phosphogypsum, which are respectively: cement: 2 - 3%, bentonite: 5%. The rotation speed of rolling granulation is 70 - 85 r / min, and the rolling duration should not exceed 20 min.

[0036] S4: Stack and cure the phosphogypsum aggregate under natural conditions for 28 days. During the natural curing period, it should be placed in a dry and cool place, without turning the pile, and pay attention to avoiding direct contact with rainwater. After curing, its compressive strength is 1 - 10 MPa.

[0037] All embodiments involved in the present invention are carried out according to the above implementation process. The difference between each embodiment lies in the proportions of phosphogypsum, cement, and bentonite when preparing the mixed dry materials. In the following embodiments, the phosphogypsum is taken from the phosphogypsum powder naturally air-dried at a certain stacking yard of Yuntianhua.

[0038] Embodiment 1:

[0039] In this embodiment, the mass percentages of each raw material are based on the mass of phosphogypsum, which are respectively for the first feeding: cement 4%, bentonite 5%, water 35%; for the second feeding: cement 2.5%, bentonite 5%. The agglomeration rate of the agglomerates prepared by the ratio of this embodiment reaches 78%, the average particle size of the agglomerates is 8 mm, the average compressive strength after 28 days of curing is 5.1 MPa, and the natural stacking porosity of the prepared phosphogypsum-based agglomerate soil aggregate is 1.6.

[0040] Embodiment 2:

[0041] In this embodiment, the mass percentages of each raw material are based on the mass of phosphogypsum, which are respectively for the first feeding: cement 4%, bentonite 7.5%, water 35%; for the second feeding: cement 2.5%, bentonite 5%. The agglomeration rate of the agglomerates prepared by the ratio of this embodiment reaches 84%, the average particle size of the agglomerates is 9 mm, the average compressive strength after 28 days of curing is 5.5 MPa, and the natural stacking porosity of the prepared phosphogypsum-based agglomerate soil aggregate is 1.3.

[0042] Embodiment 3:

[0043] In this embodiment, the mass percentages of each raw material are based on the mass of phosphogypsum, which are respectively for the first feeding: cement 4%, bentonite 9%, water 35%; for the second feeding: cement 2.5%, bentonite 5%. The agglomeration rate of the agglomerates prepared by the ratio of this embodiment reaches 91%, the average particle size of the agglomerates is 11 mm, the average compressive strength after 28 days of curing is 5.3 MPa, and the natural stacking porosity of the prepared phosphogypsum-based agglomerate soil aggregate is 1.1.

[0044] Embodiment 4:

[0045] In this embodiment, the mass percentages of each raw material are based on the mass of phosphogypsum, which are respectively for the first feeding: cement 3%, bentonite 7.5%, water 35%; for the second feeding: cement 2.5%, bentonite 5%. The agglomeration rate of the agglomerates prepared by the ratio of this embodiment reaches 81%, the average particle size of the agglomerates is 7 mm, the average compressive strength after 28 days of curing is 3.1 MPa, and the natural stacking porosity of the prepared phosphogypsum-based agglomerate soil aggregate is 1.3.

[0046] Embodiment 5:

[0047] In this embodiment, the mass percentages of the raw materials are based on the mass of phosphogypsum, and are respectively for the first feeding: cement 5%, bentonite 7.5%, water 35%; for the second feeding: cement 2.5%, bentonite 5%. The agglomeration rate of the agglomerates prepared according to the ratio of this embodiment reaches 89%, the average particle size of the agglomerates is 9 mm, the average compressive strength after 28 days of curing is 8.1 MPa, and the natural packing porosity of the phosphogypsum-based agglomerate soil aggregate prepared is 1.1.

[0048] Although the present invention has been described in detail above with general descriptions, specific embodiments and experiments, some modifications or improvements can be made on the basis of the present invention, which are obvious to those skilled in the art. Therefore, these modifications or improvements made without departing from the spirit of the present invention all fall within the scope of protection required by the present invention.

Claims

1. Preparation process of a semi-rigid agglomerated soil geotextile filler, comprising: S1: Mix the dried cement and bentonite mixture with the crushed phosphogypsum in a drum granulator. The usage amount of the dried cement is 3-5% of the mass of the phosphogypsum, and the usage amount of the bentonite is 5-9% of the mass of the phosphogypsum to obtain a first material; S2: The first material is granulated by rolling in a drum granulator. The inclination angle of the granulator is 30°-45°, the rotation speed of rolling granulation is 70-85 r / min, the rolling duration is 10-15 min, water is sprayed and injected during the rolling process, the water addition speed ≤ 1.25 mL / min, and the water usage amount is 25-35% of the mass of the phosphogypsum. After shaping, a spherical intermediate body is formed; S3: Evenly sprinkle cement and bentonite on the surface of the intermediate body. The usage amount of the cement is 2-3% of the mass of the phosphogypsum, and the usage amount of the bentonite is 5% of the mass of the phosphogypsum. Continue rolling granulation. The rolling rotation speed of the granulator is 70-85 r / min, and the rolling duration does not exceed 20 min to obtain a phosphogypsum agglomerate; S4: Place the phosphogypsum agglomerate in a dry and shady condition for stacking and curing for 28 days to obtain the semi-rigid agglomerated soil geotextile filler. The compressive strength of this geotextile filler is 1-10 MPa.

2. According to the preparation process described in claim 1, wherein: In step S1, the inclination angle of the drum granulator is 45°-55°, the stirring rotation speed is 70-85 r / min, and the stirring duration is 10-15 min.

3. A semi-rigid agglomerated soil geotextile filler prepared by the preparation process described in claim 1 or 2.

Images