A method for preparing graded porous aggregate soil using phosphogypsum

Abstract

This invention discloses a method for preparing graded porous aggregate-type soil using phosphogypsum. The main steps of the method include: adding air-dried phosphogypsum, cement, bentonite, and plant straw into a granulator in a certain proportion; spraying a certain amount of water in batches; and continuing to rotate the granulator to obtain aggregates; the aggregates are then treated with CO2 mineralization to obtain phosphogypsum-based aggregates with suitable acidity and alkalinity; preparing porous soil aggregates according to gradation requirements; composting to prepare organic fertilizer; and mixing the phosphogypsum-based soil aggregates and organic fertilizer to obtain soil suitable for planting. The soil obtained by this invention has a graded porous structure with large pores between particles and micropores within particles, good water permeability and air permeability, sufficient fertility, and good water stability of the aggregates. It can effectively solve the problem of compaction in the existing utilization of phosphogypsum soil. The method is simple to operate, has low material costs, and requires mature equipment, making it particularly suitable for providing a high-quality and inexpensive source of planting soil for rocky desertification areas.

Description

Technical Field

[0001] This invention belongs to the field of industrial solid waste resource utilization, specifically relating to a method for preparing graded porous aggregate soil using phosphogypsum. Background Technology

[0002] Phosphogypsum is a solid waste generated during the wet-process phosphoric acid production process. Its main components are calcium sulfate dihydrate and calcium sulfate hemihydrate, followed by calcium sulfate, residual phosphate rock, fluorides, acid-insoluble substances, and organic matter. With the rapid development of my country's industry, the stockpiled amount of phosphogypsum has exceeded 700 million tons and is still increasing annually. Long-term stockpiling of phosphogypsum not only wastes a large amount of land resources, but also causes the accumulation and leaching of soluble phosphorus, fluorine, and heavy metals within the stockpile, severely polluting water sources and soil around the stockpile. Furthermore, long-term stockpiled phosphogypsum, after air-drying, becomes powdery and easily generates dust during storage and transportation, polluting the atmosphere. Therefore, it is urgent to explore an efficient and environmentally friendly method for the harmless treatment of phosphogypsum.

[0003] Currently, the resource utilization of phosphogypsum is mainly focused on the construction and chemical industries. However, due to factors such as high initial processing costs and competition from existing comprehensive utilization of construction solid waste, the use of phosphogypsum as a recyclable chemical and building material still faces significant limitations. Meanwhile, utilizing phosphogypsum to improve soil has become a research hotspot in recent years. Phosphogypsum is rich in elements essential for crop growth, such as phosphorus (P), sulfur (S), and calcium (Ca), as well as organic matter and other nutrients, and can be used as a conditioner to improve the soil environment. Soil improvement using phosphogypsum or its soil-based utilization not only provides crops with the necessary nutrients but also allows the soil to accumulate organic carbon and improve its physical properties.

[0004] Practice has shown that while directly mixing phosphogypsum into soil can provide temporary improvement, the soil is more prone to compaction after one or two years of cultivation. The main reasons for compaction are: First, phosphogypsum originally contains a small amount of aggregates, but these aggregates are weakly cemented, especially when exposed to water, and gradually disappear over time, becoming a soil layer mainly composed of silt. Fine particles, carried by water, continuously infiltrate downwards, filling the pores between coarse particles, causing the entire soil to cement into clumps. Second, the trace organic matter in phosphogypsum is rapidly depleted during cultivation, further exacerbating compaction. Therefore, before mixing phosphogypsum with the soil to be treated, it is necessary to perform agglomeration treatment. This serves two purposes: firstly, to fix the harmful elements in the phosphogypsum and reduce environmental pollution during storage; and secondly, to increase the porosity between the aggregates in the mixed soil, while slowing down the release rate of various trace elements from the phosphogypsum, thereby eliminating compaction.

[0005] Currently, there are no proposed or applied methods for soil conversion of phosphogypsum group polymers, and there is also a lack of a method for phosphogypsum group polymer soil conversion treatment that can achieve a streamlined process. Summary of the Invention

[0006] The technical problem to be solved by this invention is how to use phosphogypsum to prepare soil aggregates suitable for planting. In view of the above-mentioned shortcomings of the existing technology, this invention provides a method for preparing graded porous aggregate soil using phosphogypsum, so as to realize the large-scale treatment of phosphogypsum waste generated in industry.

[0007] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows:

[0008] First, phosphogypsum is subjected to agglomeration treatment. Then, the resulting phosphogypsum aggregates are used as the soil matrix and mixed with organic fertilizers to formulate a graded porous aggregate soil with good permeability and aeration, good water stability, and sufficient nutrients. The specific steps include:

[0009] S1 Mixed Dry Material: Freshly dried phosphogypsum, cement, bentonite, bagasse or other plant straw are added to a granulator in a certain proportion. A certain amount of water is sprayed into the granulator. The granulator continues to rotate for a certain period of time to complete the agglomeration of the mixture and obtain a single-layer open structure agglomerate with a diameter of 0.25 to 10 mm.

[0010] S2 CO2 mineralization curing: The above-obtained agglomerates are placed in a CO2 mineralization curing kettle and cured for a certain period of time to obtain phosphogypsum group aggregates with suitable acidity and alkali.

[0011] S3 Preparation of Soil Aggregate: The obtained phosphogypsum group polymer is screened and divided into three particle sizes: coarse, medium and fine. Then, porous soil aggregate is prepared according to the gradation requirements.

[0012] S4 Organic Fertilizer Preparation: Using plant straw, kitchen waste, animal manure, wood waste and a small amount of natural soil as raw materials, mix them and compost them under natural conditions for 20-30 days to prepare organic fertilizer.

[0013] S5 Mixed Soil: The above-obtained phosphogypsum-based soil aggregate is mixed with organic fertilizer to produce porous, highly fertile soil for agricultural planting.

[0014] Furthermore, the bagasse or other plant straw mentioned in step S1 is obtained by a straw shredding machine. During the shredding process, appropriate moisture needs to be added to soften the straw fibers. The required straw fibers should be 10–50 mm in length and have a moisture content of 10%–15%. The straw fibers increase the cohesive force of the aggregates, and after decomposition, they provide organic matter to the soil and can form micropores within the aggregates.

[0015] Further, in step S1, the mass ratio of phosphogypsum, cement, bentonite, water, bagasse or other plant straw is 20:1:2:(4-6):2.

[0016] Furthermore, in step S1, water needs to be sprayed evenly onto the surface of the mixture, and the spraying speed must not exceed 1.25 mL / min. The spraying should be done in stages, specifically including:

[0017] S11: During the rotation of the granulator, spray 2 / 3 of the water continuously and evenly onto the surface of the mixture, then stop spraying water;

[0018] S12: Observe the agglomeration effect, and intermittently spray the remaining water onto the surface of the mixture that has not yet agglomerated to ensure that the agglomeration rate of the mixture is greater than 85%.

[0019] Furthermore, in step S1, a disc granulator is used to form granules. The tilt angle of the granulator is 45° to 55°, and the rotation speed of the granulator is controlled at 60 to 70 r / min.

[0020] Furthermore, in step S2, a CO2 mineralization curing vessel is used to cure the phosphogypsum group aggregates. During the curing process, the aggregates need to be turned over regularly to ensure that all aggregate surfaces are in full contact with CO2. The concentration of CO2 and the curing time are adjusted according to the target pH.

[0021] Furthermore, the critical sieve particle sizes of the coarse, medium, and fine phosphogypsum group aggregates mentioned in step S3 are 4.75 mm and 0.3 mm, respectively. The mass ratio of the coarse, medium, and fine phosphogypsum group aggregates is 3:2:1 to ensure that the natural packing porosity of the prepared soil aggregate is greater than 1.5.

[0022] Further, in step S5, a mixer is used to uniformly mix the phosphogypsum-based soil aggregate with organic fertilizer at a mass ratio of 5:1 to 9:1 to obtain soil. The phosphogypsum-based soil aggregate contains large pores, providing the main channels for water and air permeability. In addition, the plant straw within the phosphogypsum aggregates slowly decomposes into organic matter over time, providing further organic matter for plants, while simultaneously forming numerous micropores within the aggregates, increasing the soil's water and air permeability. The large pores between the aggregates and the micropores within the aggregates together constitute a hierarchical porous soil structure.

[0023] The present invention also discloses a graded porous aggregate type soil prepared according to the above preparation method.

[0024] Compared with the prior art, the beneficial effects of the present invention are:

[0025] 1. This invention proposes a method for soil treatment of phosphogypsum. The required raw materials include phosphogypsum, cement, bentonite, plant straw, water, kitchen waste, animal manure, wood waste, and a small amount of natural soil. Except for phosphogypsum, the other additives are easy to obtain in batches, have low cost, and require small amounts, which can significantly reduce the economic cost of phosphogypsum treatment.

[0026] 2. This invention proposes to use a disc granulator for agglomeration treatment of phosphogypsum, followed by CO2 mineralization curing for alkali reduction treatment. The required equipment is mature, the implementation process is simple, and it is easy to realize a production line processing technology in a workshop environment. The obtained phosphogypsum group aggregates are easy to transport and store for subsequent processing, which can effectively solve the environmental pollution caused by dust during the transportation and storage of phosphogypsum.

[0027] 3. In the phosphogypsum soil conversion method proposed in this invention, the phosphogypsum is first subjected to agglomeration treatment, and then the resulting phosphogypsum group aggregates are used as the main body in combination with organic fertilizers. This not only solves the problem of insufficient organic matter and rapid depletion of phosphogypsum in existing direct mixing methods, but also ensures that the phosphogypsum group aggregates have a certain strength and good water stability, making them less prone to compaction during long-term cultivation.

[0028] 4. This invention proposes a method for preparing graded porous aggregate-type soil using phosphogypsum. The phosphogypsum group aggregates obtained through pretreatment are single-layer open-structure aggregates, which can solidify heavy metals in the phosphogypsum and control the slow release of elements such as P, S, and Ca from the phosphogypsum. Furthermore, the graded porous soil structure, formed by the large pores between the aggregates and the micropores within the aggregates, ensures the long-term high permeability and aeration of the prepared soil. Attached Figure Description

[0029] Figure 1 This is a process flow diagram of the present invention.

[0030] Figure 2 This is a schematic diagram illustrating an application scenario of using phosphogypsum to produce graded porous aggregate-type soil. Detailed Implementation

[0031] The specific embodiments of the present invention will be described in detail below. For those skilled in the art, various corresponding modifications and variations can be made according to the present invention, and all such modifications and variations fall within the protection scope of the claims of the present invention.

[0032] This invention provides a method for preparing graded porous aggregate-type soil using phosphogypsum, the specific implementation process of which is as follows:

[0033] (1) Fresh air-dried phosphogypsum, cement, bentonite, bagasse or other plant straw are added to a disc granulator in a mass ratio of 40:2:4:(8~10):4 and dry-mixed to obtain a mixed dry material.

[0034] (2) Adjust the tilt angle of the granulator to 45°~55° and control the rotation speed of the granulator to 60~70r / min. After continuously and evenly spraying 2 / 3 of the water onto the surface of the mixture, stop spraying water. Then observe the agglomeration effect and intermittently spray the remaining water onto the surface of the mixture that has not yet agglomerated. Keep the granulator rotating to ensure that the agglomeration rate of the mixture is greater than 85% and complete the agglomeration treatment of phosphogypsum.

[0035] (3) Place the above-obtained agglomerates in a CO2 mineralization curing kettle for curing for a certain period of time. Adjust the CO2 concentration and curing time according to the target pH. At the same time, turn the agglomerates in the curing kettle regularly to obtain phosphogypsum group aggregate soil aggregate.

[0036] (4) The phosphogypsum group aggregates prepared above are sieved, and the critical sieve particle sizes of 4.75 mm and 0.3 mm are used to divide them into three aggregate sizes: coarse, medium and fine. Then, according to the ratio of coarse, medium and fine aggregates of 3:2:1 (mass ratio), phosphogypsum group aggregate soil aggregates with a natural packing porosity greater than 1.5 are prepared.

[0037] (5) Use plant straw, kitchen waste, animal manure, wood waste and a small amount of natural soil as raw materials, mix them and compost them under natural conditions for 20-30 days to prepare organic fertilizer. This step can also be carried out before the above steps.

[0038] (6) Use a mixer to mix the obtained phosphogypsum-based soil aggregate and organic fertilizer in a mass ratio of 5:1 to 9:1 to complete the soil treatment of phosphogypsum.

[0039] like Figure 2 As shown, the graded porous aggregate soil prepared with phosphogypsum is laid in the rocky desertification area, and crops or other green plants are planted on it. This not only enables the large-scale treatment of phosphogypsum fertilizer, but also effectively addresses the problem of rocky desertification.

[0040] The following examples illustrate the present invention. All examples are carried out according to the above-described implementation process. The differences between the examples lie in the mass ratio of phosphogypsum, cement, bentonite, water, and bagasse or other straw powder when preparing the mixed dry materials, as well as the mass ratio of phosphogypsum group polymers to organic fertilizers. In the following examples, the phosphogypsum is phosphogypsum powder taken from a stockpile of Yuntianhua and naturally air-dried.

[0041] Example 1:

[0042] In this embodiment, the mass ratio of phosphogypsum, cement, bentonite, water, and bagasse is 20:1:2:4:2. Following the above steps, phosphogypsum aggregates are prepared with an agglomeration rate of 85% and an average particle size of 5 mm. After curing for 2 days, the natural packing void ratio of the phosphogypsum aggregate soil aggregate is 1.1 after screening and preparation. The mass ratio of the phosphogypsum aggregate soil aggregate to organic fertilizer is 5:1.

[0043] Example 2:

[0044] In this embodiment, the mass ratio of phosphogypsum, cement, bentonite, water, and bagasse is 20:1:2:5:2. Following the above steps, phosphogypsum aggregates are prepared with an agglomeration rate of 85% and an average particle size of 5 mm. After curing for 2 days, the natural packing porosity of the phosphogypsum aggregate soil aggregate is 1.1 after sieving and preparation. The mass ratio of the phosphogypsum aggregate soil aggregate to organic fertilizer is 5:1.

[0045] Example 3:

[0046] In this embodiment, the mass ratio of phosphogypsum, cement, bentonite, water, and bagasse is 20:1:2:6:2. Following the above steps, phosphogypsum aggregates are prepared with an agglomeration rate of 85% and an average particle size of 5 mm. After curing for 2 days, the natural packing porosity of the phosphogypsum aggregate soil aggregate is 1.1 after screening and preparation. The mass ratio of the phosphogypsum aggregate soil aggregate to organic fertilizer is 5:1.

[0047] Example 4:

[0048] In this embodiment, the mass ratio of phosphogypsum, cement, bentonite, water, and bagasse is 20:1:2:4:2. Following the above steps, phosphogypsum aggregates are prepared with an agglomeration rate of 85% and an average particle size of 5 mm. After curing for 2 days, the natural packing porosity of the phosphogypsum aggregate soil aggregate is 1.1 after screening and preparation. The mass ratio of the phosphogypsum aggregate soil aggregate to organic fertilizer is 6:1.

[0049] Example 5:

[0050] In this embodiment, the mass ratio of phosphogypsum, cement, bentonite, water, and bagasse is 20:1:2:5:2. Following the above steps, phosphogypsum aggregates are prepared with an agglomeration rate of 85% and an average particle size of 5 mm. After curing for 2 days, the natural packing porosity of the phosphogypsum aggregate soil aggregate is 1.1 after screening and preparation. The mass ratio of the phosphogypsum aggregate soil aggregate to organic fertilizer is 7:1.

[0051] Example 6:

[0052] In this embodiment, the mass ratio of phosphogypsum, cement, bentonite, water, and bagasse is 20:1:2:6:2. Following the above steps, phosphogypsum aggregates are prepared with an agglomeration rate of 85% and an average particle size of 5 mm. After curing for 2 days, the natural packing porosity of the phosphogypsum aggregate soil aggregate is 1.1 after screening and preparation. The mass ratio of the phosphogypsum aggregate soil aggregate to organic fertilizer is 9:1.

[0053] It should be noted that the above embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential adjustments made by those skilled in the art based on the content of the present invention are within the scope of protection of the present invention.

Claims

1. A method for preparing graded porous aggregate-type soil using phosphogypsum, comprising: S1 Mixed dry material: Add air-dried phosphogypsum, cement, bentonite, and plant straw into the granulator in a mass ratio of 20:1:2:(4~6):2, spray a certain amount of water in batches, and continue to rotate the granulator to obtain agglomerates; S2 CO2 mineralization curing: The aggregates are placed in a CO2 mineralization curing kettle and cured for a certain period of time to obtain phosphogypsum group aggregates; S3 Soil aggregate preparation: The phosphogypsum group polymer is screened and divided into three particle sizes: coarse, medium and fine. Then, it is formulated according to the gradation requirements to obtain phosphogypsum-based soil aggregate. S4 Soil Mixture: Different particle sizes of phosphogypsum-based soil aggregates are mixed with organic fertilizer at a mass ratio of 5:1 to 9:

1. The mass ratio of coarse, medium, and fine phosphogypsum-based soil aggregates of different particle sizes is 3:2:1, resulting in a graded porous aggregated soil. The plant straw is crushed, softened, and filamentized, with a filament length of 10-50 mm and a moisture content of 10%-15%.

2. The method according to claim 1, wherein: In step S1, the water spraying speed is ≤1.25 mL / min.

3. The method according to claim 1, wherein: Step S1, which involves spraying a certain amount of water in batches, includes: S11: During the rotation of the granulator, after spraying 2 / 3 of the water onto the surface of the mixture, stop adding water; S12: Observe the agglomeration effect. Intermittently spray the remaining water onto the surface of the mixture that has not yet agglomerated, so that the agglomeration rate is greater than 85%.

4. The method according to claim 1, wherein: The critical sieve particle sizes of the coarse, medium, and fine agglomerates described in step S3 are 4.75 mm and 0.3 mm, respectively.

5. The method according to claim 1, wherein: The organic fertilizer mentioned in step S4 is prepared by the following method: Organic fertilizer is prepared by mixing plant straw, kitchen waste, animal manure, wood waste and natural soil as raw materials and composting them under natural conditions for 20-30 days.

6. A graded porous aggregate soil obtained by the method for preparing graded porous aggregate soil using phosphogypsum according to any one of claims 1 to 5.

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