A new four-layer structure of phosphogypsum-based high and steep slope greening spraying material

Abstract

The present invention discloses a novel phosphogypsum-based high-steep slope greening spraying material with a four-layer structure. 1) The novel phosphogypsum-based high-steep slope greening spraying material with a four-layer structure comprises, from bottom to top, a bottom fixing layer, a middle nutrient layer, an upper planting layer, and a surface curing layer. The present invention can realize direct spraying construction without hanging a mesh under slope conditions with a slope of less than 80 degrees, greatly reducing construction costs and difficulty. At the same time, it overcomes the defects of the above-mentioned existing slope repair technology using phosphogypsum, avoids various risks therein, improves the comprehensive utilization efficiency of phosphogypsum, and can quickly and effectively carry out slope protection and green plant restoration.

Description

Technical Field

[0001] The invention relates to the technical field of comprehensive utilization of phosphogypsum, in particular to a novel phosphogypsum-based high and steep slope greening spraying material with a four-layer structure. Background Art

[0002] Phosphogypsum is a byproduct of wet-process phosphoric acid production, with five tons of it produced for every ton of phosphoric acid produced. Currently, my country produces nearly 80 million tons of phosphogypsum annually, with 800 million tons in stockpiles and a utilization rate of only 45%. As phosphogypsum stockpiles continue to grow, the demand for land for slag storage is also increasing, increasing environmental risks. Consequently, the government is placing increasing emphasis on the utilization of phosphogypsum, introducing a number of policy indicators to ensure its effective use and minimize its impact on production, daily life, and the environment.

[0003] At the same time, with the rapid development of the national economy, mining, highway, railway, urban construction and other projects continue to increase. Due to a large amount of filling and mountain excavation, many exposed slopes are formed, and the original natural vegetation is severely damaged, resulting in soil erosion, ecological imbalance, and adverse effects on the environment. Therefore, technical measures need to be taken to repair and green the slopes. Traditional slope greening methods mostly use imported soil spraying technology, but imported soil has low adhesion and low strength, and is prone to landslides and loss under conditions of heavy rainfall; in order to overcome the shortcomings of imported soil, people have successively developed ecological concrete spraying technology, but this technology uses a large amount of cement, resulting in a high alkalinity of the material, and cement is not compatible with clay (soil). After solidification, it will shrink, resulting in local cracking and severe compaction after construction, which is not conducive to plant germination and growth. When constructing on slopes with larger slopes, anchor rods and hanging nets must be fixed in advance, which makes construction difficult and costly. On this basis, people have developed a series of slope repair technologies related to phosphogypsum based on the characteristics of phosphogypsum. Overall, the existing technology has the following defects and shortcomings:

[0004] 1. Most existing technologies use unmodified or harmless phosphogypsum raw materials (raw slag), or only add a small amount of hemihydrate gypsum (α-type or β-type) formed after calcination or crystallization treatment as a coagulant in the formula. On the one hand, the direct use of phosphogypsum raw materials (raw slag) is equivalent to piling it somewhere other than the slag storage, which poses huge environmental, legal and policy risks. On the other hand, the main component of phosphogypsum raw materials (raw slag) is calcium sulfate dihydrate, which does not have gelling properties. Adding only a small amount of hemihydrate gypsum to the formula cannot make the material obtain the ideal strength. Additional curing agents (coagulants) are often required, which increases costs and construction difficulty. Furthermore, when the existing technology uses the calcined products of phosphogypsum, such as hemihydrate and anhydrous gypsum, as raw materials for formulation preparation, it is necessary to add a large amount of chemical synthetic admixtures such as surfactants, water reducers, thixotropic agents, water retention agents, etc., as well as certain mineral grinding aids such as silicon oxide, aluminum oxide, calcium oxide, etc., which not only greatly increases costs, but also brings potential environmental risks to the application of the material in ecological restoration, which is not conducive to large-scale promotion.

[0005] 2. Most of the spraying materials in the existing technology use a single-layer or at most double-layer structure, which cannot simultaneously meet the material's requirements for strength and plant growth function. When the spraying layer is thick or the material strength is high, it is difficult for plant seeds buried deep inside to penetrate and germinate, resulting in low germination rate and survival rate, causing waste of materials and costs, and increasing the probability of failure of ecological restoration.

[0006] 3. The addition amount of phosphogypsum in the existing technology is less than 50%. On the one hand, the utilization amount of phosphogypsum is low, and on the other hand, the added other ingredients increase the overall cost.

[0007] Therefore, a new type of four-layer structured phosphogypsum-based high and steep slope greening spraying material is urgently needed to solve the above problems. Summary of the Invention

[0008] The invention provides a novel phosphogypsum-based high and steep slope greening spraying material with a four-layer structure.

[0009] The scheme of the present invention is:

[0010] A novel four-layer phosphogypsum-based high-steep slope greening spraying material, comprising, from bottom to top, a bottom fixing layer, a middle nutrient layer, an upper planting layer, and a surface curing layer;

[0011] 2) The thickness of the novel phosphogypsum-based high and steep slope greening spraying material is 16 to 34 cm;

[0012] 3) The gypsum raw material of the novel phosphogypsum-based high and steep slope greening spraying material is derived from phosphogypsum, a by-product of wet-process phosphoric acid, and the comprehensive weight proportion of the phosphogypsum component in the novel four-layer structure phosphogypsum-based high and steep slope greening spraying material is ≥ 75%;

[0013] 4) The phosphogypsum is calcined through different processes to lose part or all of its crystal water, and its structure is transformed into hemihydrated phosphogypsum, anhydrous phosphogypsum and complex phase phosphogypsum; the complex phase phosphogypsum is a complex phase gypsum with both hemihydrate and anhydrous phases.

[0014] As a preferred technical solution, the bonding strength of the final cementitious product formed by the hydration process of the phosphogypsum is anhydrous gypsum > complex phase gypsum > hemihydrate gypsum; the phosphogypsum-based high and steep slope greening spraying material contains a gypsum retarder; when the phosphogypsum-based high and steep slope greening spraying material system contains anhydrous gypsum components, it contains an activator.

[0015] As a preferred technical solution, the thicknesses of the bottom fixing layer, the middle nutrient layer, the upper planting layer and the surface maintenance layer are 5-8 cm, 8-20 cm, 2-4 cm and 1-2 cm respectively.

[0016] As a preferred technical solution, the mass proportions of phosphogypsum in the bottom fixing layer, the middle nutrient layer, the upper planting layer and the surface maintenance layer are 85-99%, 60-75%, 30-60% and 7-15% respectively.

[0017] As a preferred technical solution, the raw materials of the bottom fixing layer include phosphogypsum, filler, matrix soil, retarder, and root guiding agent. When the phosphogypsum in the bottom fixing layer contains anhydrous phosphogypsum, the raw materials of the bottom fixing layer also include an activator.

[0018] The filler is one or more of mountain sand, river sand, machine-made sand and clay; the root guiding agent is one or more of compound fertilizer and microbial agent;

[0019] The bottom fixing layer is prepared by first mixing a portion of phosphogypsum, filler, and matrix soil in a ratio of 1:0 to 0.1:0.02 to 0.1. During this process, an appropriate amount of water is added to hydrate the gypsum. After hydration is complete, the gypsum is crushed and granulated to form a 1 cm granular prefabricated material. Finally, the prefabricated material and the remaining phosphogypsum are mixed in a ratio of 1 to 2:1, and a retarder of 0.3 to 5‰ of the remaining phosphogypsum mass and a root guiding agent of 1 to 4‰ of the total mass are added. Water is added and the material is fed into a mixing device to control the water-cement ratio to 0.4 to 0.5. After uniform mixing, the material is sprayed in layers to the construction surface to a set thickness. If the phosphogypsum contains anhydrous gypsum, an activator of 0.5 to 5% of the mass of the anhydrous gypsum is added. The gel formed by the hydration process of the phosphogypsum has excellent strength and can effectively fix the slope. Microbial agents and compound fertilizers are also introduced as plant root growth guiding agents to guide and encourage plant roots to grow and entangle toward the original slope surface, further stabilizing the slope surface.

[0020] As a preferred technical solution, the raw materials of the intermediate nutrient layer include phosphogypsum, filler, retarder, organic matter and water retaining agent; when the phosphogypsum in the intermediate nutrient layer contains anhydrous phosphogypsum, the raw materials of the intermediate nutrient layer also include an activator;

[0021] The filler is one or more of mountain sand, river sand, machine-made sand and clay; the organic matter is one or more of matrix soil, peat soil, livestock manure, humus soil, sludge, lake bottom sludge and microbial agent; the sludge is one or more of municipal sludge and domestic sludge; the water-retaining agent is one or more of biochar, grass fiber, wood fiber, perlite, vitrified microbeads, biological starch water-retaining agent, resin water-retaining agent, organic water-retaining agent, vermiculite, coal slag, ceramsite and volcanic rock particles;

[0022] The preparation method of the intermediate nutrient layer comprises the following steps: firstly mixing part of the phosphogypsum, filler, and organic matter in a ratio of 1:0 to 0.1:0.3, adding an appropriate amount of water to hydrate the gypsum, crushing the gypsum after hydration is completed, and granulating the gypsum to form a 1 cm granular prefabricated material; finally, adding the prefabricated material, the remaining phosphogypsum, and a water retaining agent in a ratio of 1:1 to 3:0.8 to 1, and then adding a retarder with a weight of 0.3-5‰ of the remaining phosphogypsum and water to a stirring device, controlling the water-cement ratio to 0.4-0.5, stirring evenly, and then spraying the mixture in layers to the surface of the bottom fixed layer to reach a set thickness; and if the phosphogypsum contains anhydrous gypsum, adding an activator with a weight of 1-5% of the weight of the anhydrous gypsum.

[0023] This layer is relatively thick, and its main function is to provide sufficient nutrients, water and growth space for plant roots. The gel formed by the hydration process of phosphogypsum has a sponge-like porous structure. While having sufficient supporting strength, it also has excellent water retention properties and provides sufficient growth space for plant roots.

[0024] As a preferred technical solution, the raw materials of the upper planting layer include phosphogypsum, filler, retarder, organic matter, water-retaining agent and plant seeds; when the phosphogypsum in the upper planting layer contains anhydrous phosphogypsum, the raw materials of the upper planting layer also include an activator; the mass of the plant seeds is 1 to 3‰ of the total mass of the materials of the upper planting layer;

[0025] The filler is one or more of mountain sand, river sand, machine-made sand and clay; the organic matter is one or more of matrix soil, peat soil, livestock manure, humus soil, sludge, lake bottom sludge and microbial agent; the sludge is one or more of municipal sludge and domestic sludge; the water-retaining agent is one or more of biochar, grass fiber, wood fiber, perlite, vitrified microbeads, biological starch water-retaining agent, resin water-retaining agent, organic water-retaining agent, vermiculite, coal slag, ceramsite and volcanic rock particles;

[0026] The upper planting layer is prepared by first mixing a portion of phosphogypsum, filler, and organic matter in a ratio of 1:0.2 to 0.5:0.6 to 1, adding an appropriate amount of water to hydrate the gypsum, crushing it after hydration, and granulating it into 1 cm granular prefabricated materials. Finally, the prefabricated materials, the remaining phosphogypsum, and a water-retaining agent in a ratio of 1:0.5 to 2:1, along with a retarder (0.3-5‰ of the weight of the remaining phosphogypsum) and water, are added to a mixing device to control the water-cement ratio to 0.4-0.6. Plant seeds are added during stirring, and after uniform mixing, the materials are sprayed in layers to the surface of the middle nutrient layer to a predetermined thickness. If the phosphogypsum contains anhydrous gypsum, an activator (1-5% of the weight of the anhydrous gypsum) is added. The main function of this layer is to sow and fix plant seeds. The thickness and proportion of phosphogypsum are both small to facilitate smooth rooting and germination of the plant seeds, thereby improving the germination rate and survival rate.

[0027] The plant seeds are one or more tree species and grass species that are highly adaptable, drought-resistant, calcium-loving, have well-developed root systems, are easy to survive, grow rapidly, and have strong regeneration capabilities, especially those with strong asexual reproduction and regeneration capabilities.

[0028] As a preferred technical solution, the raw materials of the surface curing layer include phosphogypsum, water-retaining agent, plant fiber, and retarder; when the phosphogypsum in the surface curing layer contains anhydrous phosphogypsum, the raw materials of the surface curing layer also include an activator;

[0029] The water-retaining agent is one or more of perlite, vitrified microspheres, and vermiculite; the plant fiber is one or both of grass fiber and wood fiber;

[0030] Phosphogypsum, a water-retaining agent, and plant fiber are added to a mixing device in a ratio of 1:2-4:3-5, along with a retarder (0.3-5‰ by weight of the phosphogypsum) and water. The water-cement ratio is controlled at 0.3-0.4. After uniform mixing, the mixture is sprayed in layers onto the surface of the upper planting layer to a desired thickness. If the phosphogypsum contains anhydrous gypsum, an activator (1-5% by weight of the anhydrous gypsum) is added. This layer, applied to the surface of the upper planting layer, primarily serves to retain water and heat. When applied on steep slopes, this eliminates the need for manual labor to reach the top of the slope and apply a non-woven fabric or other water-retaining and heat-insulating film, improving safety and saving significant labor and material costs.

[0031] As a preferred technical solution, the particle size must be controlled below 1 cm before feeding and mixing; during spraying construction, it is necessary to wait until the underlying structure has initially solidified before proceeding.

[0032] Due to the adoption of the above technical solution, a new type of phosphogypsum-based high-steep slope greening spraying material with a four-layer structure is provided. 1) The new type of phosphogypsum-based high-steep slope greening spraying material with a four-layer structure includes, from bottom to top, a bottom fixing layer, a middle nutrient layer, an upper planting layer and a surface maintenance layer; 2) The thickness of the new type of phosphogypsum-based high-steep slope greening spraying material is 16 to 34 cm; 3) The gypsum raw material of the new type of phosphogypsum-based high-steep slope greening spraying material is derived from phosphogypsum, a by-product of wet-process phosphoric acid, and the comprehensive mass proportion of the phosphogypsum component in the new type of phosphogypsum-based high-steep slope greening spraying material with a four-layer structure is ≥75%; 4) The phosphogypsum is calcined through different processes to lose part or all of its crystalline water, and its structure is transformed into hemihydrated phosphogypsum, anhydrous phosphogypsum and complex-phase phosphogypsum; the complex-phase phosphogypsum is a complex-phase gypsum in which both hemihydrate and anhydrous phases exist.

[0033] Advantages of the present invention:

[0034] This invention mainly uses phosphogypsum that has been calcined at high temperature, and forms hemihydrate gypsum or anhydrous gypsum or a complex phase gypsum with both hemihydrate and anhydrous phases after dehydration and recrystallization. It is matched with various fillers, water retaining agents, organic matter, plant seeds and other ingredients, and does not require the addition of additional coagulants (curing agents) and complex chemical synthetic substances to form slope greening spraying materials for protection and greening of various exposed slopes. Unlike traditional soil and concrete spraying technology, the present invention utilizes the good gelling properties of semi-hydrated and anhydrous gypsum itself to achieve direct spraying construction without hanging a mesh under slope conditions with a slope of less than 80°, greatly reducing construction cost and difficulty. At the same time, the present invention overcomes the defects of the above-mentioned existing slope repair technology using phosphogypsum, avoids various risks therein, improves the comprehensive utilization efficiency of phosphogypsum, and can quickly and effectively perform slope protection and green plant restoration. It is mainly used in mine environment ecological restoration and greening, road engineering and construction site slope ecological restoration and greening, urban engineering wound ecological restoration and greening, garden landscape engineering design, garden greening maintenance, etc.

[0035] Technical advantages compared with existing technologies:

[0036] 1. The present invention uses phosphogypsum that has been calcined at high temperature as the main formula, effectively removing volatile harmful impurities in the phosphogypsum and avoiding the environmental, legal and policy risks brought about by the use of phosphogypsum slag in the prior art. At the same time, the addition of special microbial agents in the formula can slowly interact with insoluble phosphorus, calcium, sulfur, nitrogen and other elements required by plants contained in the material to form soluble products, continuously providing nutrients for plant growth in a slow-release manner, and fully utilizing the favorable advantages of phosphogypsum for plant growth.

[0037] 2. The present invention adopts phosphogypsum that has been calcined at high temperature as the main body of the formula. Its calcined product includes hemihydrated gypsum or anhydrous gypsum or a multiphase gypsum with both hemihydrate and anhydrous phases. It itself has good hydration and gelling properties and fully meets the strength requirements of slope protection. In addition, its hydration and gelling process is rapid and can be cured within tens of minutes. Compared with the existing technology, the material of the present invention does not require the addition of an additional curing agent, and can be sprayed without a mesh under the conditions of steep and self-stabilizing slopes with a slope of less than 80°. Personnel do not need to climb up steep slopes and cliffs to operate, which greatly reduces costs and construction difficulty and improves construction safety. At the same time, the ingredients in the formula of the material of the present invention, except gypsum, are preferably natural substances and domestic, municipal, and industrial solid wastes. The specific advantages of these substances are used to interact with gypsum to provide the required properties for the material of the present invention. No chemical synthetic admixtures are added, which closely follows the general direction of the essential requirements of environmental protection and ecological restoration materials, greatly reducing costs and domestic, municipal, and industrial environmental protection pressures.

[0038] 3. The present invention uses phosphogypsum that has been calcined at high temperature as the main formula. The calcined product includes hemihydrated gypsum, anhydrous gypsum, or a multi-phase gypsum containing both hemihydrate and anhydrous phases. The gel formed after hydration and coagulation has a porous sponge-like structure. This structure can provide ample growth space for plant roots. At the same time, this porous structure also gives the material excellent water retention and air permeability. Compared with the existing technology, the cost invested in water retention of this material is greatly reduced, and it also provides good conditions for plant growth, greatly improving the plant survival rate.

[0039] 4. The present invention uses phosphogypsum that has been calcined at high temperature as the main formula. Unlike cement, which has shrinkage and incompatibility with clay during solidification, the gel formed by the hydration and solidification of hemihydrated gypsum, anhydrous gypsum, or a multiphase gypsum containing both hemihydrate and anhydrous phases has micro-expansion and good compatibility with soil (clay). Compared with the existing technology, this material has excellent resistance to thermal vibration and cracking when used on slopes, avoiding cracking, collapse, sliding and loss during use.

[0040] 5. The present invention adopts phosphogypsum that has been calcined at high temperature as the main formula, and scientifically and rationally designs it into a four-layer functional gradient structure. The layers are compatible and have good transitions while each performing its own function, giving full play to the advantages of the component design of each layer. Compared with the existing technology, this material takes into account the functions of slope protection and plant growth to a greater extent, improves the slope protection strength and safety factor, greatly improves the plant germination rate and survival rate, improves the material application efficiency, saves costs, and improves the success rate of slope ecological restoration.

[0041] 6. Through a lot of creative work and experiments by technical personnel, the present invention has increased the comprehensive proportion of phosphogypsum in the material formula to 75%. Compared with the existing technology, this material has greatly improved the comprehensive utilization efficiency of phosphogypsum. DETAILED DESCRIPTION

[0042] The present invention provides a novel phosphogypsum-based high and steep slope greening spraying material with a four-layer structure to solve the problems in the above-mentioned background technology.

[0043] In order to make the technical means, creative features, objectives and effects achieved by the present invention easier to understand, the present invention is further described below in conjunction with specific embodiments.

[0044] Example 1

[0045] Construction object: The excavation slope is a strongly weathered shale base with a lot of gravel, poor water retention and no fertility. The slope is 75-80°, the height is 40m, and the total area is 3000m 2 ;

[0046] Step 1, Slope cleaning: clean the loose soil and pumice on the slope;

[0047] Step 2, construction of the bottom fixing layer: add retarder, clay, mountain sand, and microbial agent to the semi-hydrated gypsum formed by high-temperature calcination of phosphogypsum to form a prefabricated material with gypsum accounting for 85-95%. Put it into the gypsum mixer and add water to mix it into slurry with a water-cement ratio of 0.4-0.6. The mixed slurry is sent to the spraying equipment, and the air granulation system and spraying system are started. Set the angle, speed, and pressure and spray it in layers on the cleaned slope to a thickness of 6-8 cm.

[0048] Step 3, construction of the intermediate nutrient layer: After the bottom fixing layer solidifies, the semi-hydrated gypsum formed by high-temperature calcination of phosphogypsum is added with retarder, clay, mountain sand, humus, municipal / domestic sludge, biochar, wood fiber, vitrified microspheres, biological starch water-retaining agent, and microbial agent to form a prefabricated material, with gypsum accounting for 50-60%. The prefabricated material is placed in a gypsum mixer and mixed with water to form a slurry with a water-cement ratio of 0.4-0.5. The mixed slurry is fed into the spraying equipment, and the air granulation system and spraying system are started. The angle, speed, and pressure are set and the prefabricated material is sprayed in layers on the solidified bottom fixing layer to a thickness of 10-15 cm.

[0049] Step 4, construction of the upper planting layer: After the middle nutrient layer solidifies, the semi-hydrated gypsum formed by high-temperature calcination of phosphogypsum is added with retarder, clay, mountain sand, humus, municipal / domestic sludge, biochar, wood fiber, vitrified microspheres, biological starch water-retaining agent, microbial agent and plant seeds to form a prefabricated material. The gypsum component accounts for 20-30%, and the mass of the plant seeds is 1-3‰ of the total mass of the planting layer material. The material is placed in a gypsum mixer and water is added to form a slurry with a water-cement ratio of 0.4-0.45. The mixed slurry is sent to the spraying equipment, and the air granulation system and spraying system are started. The angle, speed and pressure are set and the material is sprayed in layers on the solidified middle nutrient layer to a thickness of 2-3 cm.

[0050] Process 5, construction of surface curing layer: After the upper planting layer is solidified, the semi-hydrated gypsum formed by high-temperature calcination of phosphogypsum is added with retarder, perlite, grass fiber and wood fiber to form a prefabricated material, with the gypsum content accounting for 10-15%. Put it into the gypsum mixer and add water to mix into slurry with a water-cement ratio of 0.3-0.35. The mixed slurry is sent to the spraying equipment, and the air granulation system and the spraying system are started. The angle, speed and pressure are set and sprayed in layers on the solidified upper planting layer with a thickness of 1-1.5 cm.

[0051] After the construction is completed, the seeds begin to sprout after one week of normal maintenance, with a germination rate of more than 95%. After 28 days, the compressive strength of the base layer can reach 4MPa. Since the base materials are all hemihydrate gypsum, the transition between the layers is uniform, the bonding state is good, and there is no stratification. After being washed by heavy rain, there is no loss or landslide. After 12 months, the plant survival rate is more than 90%.

[0052] Example 2

[0053] Construction object: The excavation of a rock pile slope in a certain project is a limestone base with a lot of gravel, poor water retention, and no fertility. The slope is 45-50°, the height is 10m, and the total area is 500m 2 ;

[0054] Step 1, Slope cleaning: clean the loose soil and pumice on the slope;

[0055] Step 2, construction of the bottom fixing layer: add an activator, retarder, mountain sand, and microbial agent to anhydrous gypsum formed by high-temperature calcination of phosphogypsum to form a prefabricated material with gypsum accounting for 85-95%. Put it into a gypsum mixer and add water to mix it into slurry with a water-cement ratio of 0.4-0.6. The mixed slurry is sent to the spraying equipment, and the air granulation system and spraying system are started. Set the angle, speed, and pressure and spray it in layers on the cleaned slope to a thickness of 5-7 cm.

[0056] Step 3, construction of the intermediate nutrient layer: After the bottom fixing layer solidifies, the anhydrous gypsum formed by high-temperature calcination of phosphogypsum is added with an activator, retarder, clay, mountain sand, peat soil, livestock manure, wood fiber, perlite, organic water-retaining agent, ceramsite, and microbial agent to form a prefabricated material, with gypsum accounting for 50-60%. The prefabricated material is placed in a gypsum mixer and water is added to form a slurry with a water-cement ratio of 0.4-0.5. The mixed slurry is sent to the spraying equipment, and the air granulation system and spraying system are started. The angle, speed, and pressure are set and the prefabricated material is sprayed in layers on the solidified bottom fixing layer to a thickness of 8-13 cm.

[0057] Step 4, construction of the upper planting layer: After the middle nutrient layer solidifies, the anhydrous gypsum formed by high-temperature calcination of phosphogypsum is added with an activator, retarder, clay, mountain sand, peat soil, livestock manure, wood fiber, perlite, organic water-retaining agent, ceramsite, microbial agent and plant seeds to form a prefabricated material. The gypsum component accounts for 20-30%, and the mass of the plant seeds is 1-3‰ of the total mass of the planting layer material. The prefabricated material is placed in a gypsum mixer and water is added to form a slurry with a water-cement ratio of 0.4-0.45. The mixed slurry is sent to the spraying equipment, and the air granulation system and spraying system are started. The angle, speed and pressure are set and the prefabricated material is sprayed in layers on the solidified middle nutrient layer to a thickness of 2-2.5 cm.

[0058] Process 5, construction of the surface curing layer: After the upper planting layer solidifies, the anhydrous gypsum formed by high-temperature calcination of phosphogypsum is added with activator, retarder, perlite, grass fiber, and wood fiber to form a prefabricated material, with the gypsum content accounting for 10-15%. Put it into the gypsum mixer and add water to mix into slurry with a water-cement ratio of 0.3-0.35. The mixed slurry is sent to the spraying equipment, and the air granulation system and the spraying system are started. The angle, speed, and pressure are set and sprayed in layers on the solidified upper planting layer with a thickness of 1-1.5 cm.

[0059] After the construction is completed, the seeds begin to sprout after one week of normal maintenance, with a germination rate of more than 95%. After 28 days, the compressive strength of the base layer can reach 8MPa. Since the base materials are all anhydrous gypsum, the transition between layers is uniform, the bonding state is good, and there is no stratification. After being washed by heavy rain, there is no loss or landslide. After 12 months, the plant survival rate is more than 90%.

[0060] Example 3

[0061] Construction object: excavation of earth and stone slope of a road project, with a soil-stone base, containing a lot of gravel, poor water retention, weak fertility, slope of 55-65°, height of 5m, and a total area of ​​2000m 2 ;

[0062] Step 1, Slope cleaning: clean the loose soil and pumice on the slope;

[0063] Step 2, construction of the bottom fixing layer: Add activator, retarder, clay, mountain sand, and microbial agent to the complex phase gypsum formed by high-temperature calcination of phosphogypsum to form a prefabricated material, with gypsum accounting for 85-95%. Put it into a gypsum mixer and add water to mix it into a slurry with a water-cement ratio of 0.4-0.6. The mixed slurry is sent to the spraying equipment, and the air granulation system and spraying system are started. The angle, speed, and pressure are set and the slurry is sprayed in layers on the cleaned slope to a thickness of 5-6 cm.

[0064] Step 3, construction of the intermediate nutrient layer: After the bottom fixing layer solidifies, the composite gypsum formed by high-temperature calcination of phosphogypsum is added with an activator, retarder, machine-made sand, clay, peat, humus, lake bottom silt, wood fiber, perlite, resin water-retaining agent, coal furnace slag, and microbial agent to form a prefabricated material, with gypsum accounting for 50-60%. The prefabricated material is placed in a gypsum mixer and mixed with water to form a slurry with a water-cement ratio of 0.4-0.5. The mixed slurry is fed into the spraying equipment, and the air granulation system and spraying system are started. The angle, speed, and pressure are set and the prefabricated material is sprayed in layers on the solidified bottom fixing layer to a thickness of 8-11 cm.

[0065] Step 4, construction of the upper planting layer: After the middle nutrient layer solidifies, the composite gypsum formed by high-temperature calcination of phosphogypsum is added with an activator, retarder, machine-made sand, clay, peat, humus, lake bottom silt, wood fiber, perlite, resin water-retaining agent, coal slag, microbial agent and plant seeds to form a prefabricated material. The gypsum component accounts for 20-30%, and the mass of the plant seeds is 1-3‰ of the total mass of the planting layer material. The prefabricated material is placed in a gypsum mixer and water is added to form a slurry with a water-cement ratio of 0.4-0.45. The mixed slurry is sent to the spraying equipment, and the air granulation system and spraying system are started. The angle, speed and pressure are set and the prefabricated material is sprayed in layers on the solidified middle nutrient layer to a thickness of 2-2.5 cm.

[0066] Process 5, construction of the surface curing layer: After the upper planting layer is solidified, the complex phase gypsum formed by high-temperature calcination of phosphogypsum is added with activator, retarder, perlite, grass fiber and wood fiber to form a prefabricated material, with the gypsum content accounting for 10-15%. Put it into the gypsum mixer and add water to mix into slurry with a water-cement ratio of 0.3-0.35. The mixed slurry is sent to the spraying equipment, and the air granulation system and the spraying system are started. The angle, speed and pressure are set and sprayed in layers on the solidified upper planting layer with a thickness of 1-1.5 cm.

[0067] After the construction is completed, the seeds begin to sprout after one week of normal maintenance, with a germination rate of more than 95%. After 28 days, the compressive strength of the base layer can reach 6MPa. Since the base materials are all phosphorus-complex phase gypsum, the transition between each layer is uniform, the bonding state is good, and there is no stratification. After being washed by strong rainwater, there is no loss or landslide. After 12 months, the plant survival rate is more than 90%.

[0068] The present invention uses hemihydrated gypsum or anhydrous gypsum or multiphase gypsum containing both hemihydrated and anhydrous phases, which is obtained by calcining and recrystallizing phosphogypsum at high temperature, to prepare the slope greening spraying material. On the one hand, most of the harmful impurities in the phosphogypsum are removed during the high-temperature treatment process. On the other hand, the hemihydrated gypsum or anhydrous gypsum or multiphase gypsum containing both hemihydrated and anhydrous phases, which has good gelling properties, provides sufficient strength for the material. The porous sponge-like structure of the gypsum gel provides good water retention and air permeability for plant growth. At the same time, the present invention screens other raw materials in the material formula except gypsum, gives priority to the use of natural substances and domestic, municipal and industrial solid wastes, and utilizes the specific advantages of these substances to interact with gypsum to provide the required properties for the material of the present invention. No chemical synthetic admixtures are added, and the material adheres closely to the general direction of the essential requirements of environmental protection and ecological restoration materials, thereby greatly reducing costs and domestic and municipal environmental protection pressures.

[0069] The present invention provides a multi-layer gradient structure with both strength and plant growth function, which increases the comprehensive proportion of phosphogypsum components in the material to 75%.

[0070] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and modifications are intended to fall within the scope of the present invention. The scope of protection claimed in the present invention is defined by the appended claims and their equivalents.

Claims

1. A new type of four-layer phosphogypsum-based high and steep slope greening spraying material, characterized by: 1) The new four-layer structure of the phosphogypsum-based high and steep slope greening spraying material includes, from bottom to top, a bottom fixing layer, a middle nutrient layer, an upper planting layer, and a surface maintenance layer; 2) The thickness of the new phosphogypsum-based high and steep slope greening spraying material is 16 to 34 cm; 3) The gypsum raw material of the novel phosphogypsum-based high-steep slope greening spraying material is derived from phosphogypsum, a by-product of wet-process phosphoric acid, and the phosphogypsum content of the novel four-layer structured phosphogypsum-based high-steep slope greening spraying material is ≥ 75% by weight; 4) The phosphogypsum is calcined through different processes to lose some or all of its crystal water, and its structure is transformed into hemihydrated phosphogypsum, anhydrous gypsum, and complex-phase phosphogypsum; the complex-phase phosphogypsum is a complex-phase gypsum with both hemihydrate and anhydrous phases; The thicknesses of the bottom fixing layer, the middle nutrient layer, the upper planting layer and the surface maintenance layer are 5-8 cm, 8-20 cm, 2-4 cm and 1-2 cm respectively; When the phosphogypsum does not contain anhydrous gypsum, the raw materials of the bottom fixing layer are composed of phosphogypsum, filler, matrix soil, retarder, and root guiding agent. The preparation method of the bottom fixing layer is as follows: first, part of the phosphogypsum, filler, and matrix soil are mixed in a ratio of 1:0 to 0.1:0.02 to 0.1, and an appropriate amount of water is added during the mixing to hydrate the gypsum. After the hydration is completed, the gypsum is crushed and granulated to form a 1 cm granular prefabricated material. Finally, the prefabricated material and the remaining phosphogypsum are mixed in a ratio of 1 to 2:1, and 0.3 to 5‰ of the retarder of the remaining phosphogypsum and 1 to 4‰ of the total mass of the root guiding agent are added. Water is added and the material is fed into a mixing device to control the water-cement ratio to 0.4 to 0.

5. After uniform mixing, the material is sprayed in layers until the construction surface reaches a set thickness. When the phosphogypsum contains anhydrous gypsum, the raw materials of the bottom fixing layer are composed of phosphogypsum, filler, matrix soil, retarder, root guiding agent, and stimulant. The preparation method of the bottom fixing layer is as follows: first, part of the phosphogypsum, filler, matrix soil, and stimulant are mixed in proportion, with the ratio of phosphogypsum, filler, and matrix soil being 1:0-0.1:0.02-0.1, and the stimulant is added at 0.5-5% of the weight of the anhydrous gypsum; during this period, an appropriate amount of water is added to hydrate the gypsum, and after hydration is completed, the gypsum is crushed and granulated to form a 1 cm granular prefabricated material; finally, the prefabricated material and the remaining phosphogypsum are mixed in a ratio of 1-2:1, and 0.3-5‰ of the weight of the retarder of the remaining phosphogypsum and 1-4‰ of the total weight of the root guiding agent are added, and water is added to the mixing equipment to control the water-cement ratio to 0.4-0.

5. After stirring evenly, the gypsum is sprayed in layers until the construction surface reaches a set thickness; The filler is one or more of mountain sand, river sand, machine-made sand and clay; the root guiding agent is one or more of compound fertilizer and microbial agent; When the phosphogypsum does not contain anhydrous gypsum, the raw materials of the surface curing layer are composed of phosphogypsum, a water-retaining agent, plant fiber, and a retarder. The preparation method of the surface curing layer is to add phosphogypsum, a water-retaining agent, and plant fiber in a ratio of 1:2-4:3-5, and then add 0.3-5‰ of the retarder by weight of the phosphogypsum and water to a mixing device, control the water-cement ratio to 0.3-0.4, stir evenly, and then spray the mixture in layers to the surface of the upper planting layer to reach a set thickness. When the phosphogypsum contains anhydrous gypsum, the raw materials of the surface curing layer are composed of phosphogypsum, a water-retaining agent, plant fiber, a retarder, and an activator. The surface curing layer is prepared by adding phosphogypsum, a water-retaining agent, and plant fiber in a ratio of 1:2-4:3-5, and then adding 1-5% of the mass of the anhydrous gypsum activator, 0.3-5‰ of the mass of the phosphogypsum retarder, and water to a mixing device, controlling the water-cement ratio to 0.3-0.4, stirring evenly, and then spraying the mixture in layers to the surface of the upper planting layer to a set thickness. The water-retaining agent is one or more of perlite, vitrified microspheres, and vermiculite; the plant fiber is one or both of grass fiber and wood fiber; When the phosphogypsum does not contain anhydrous gypsum, the raw materials of the intermediate nutrient layer are composed of phosphogypsum, filler, retarder, organic matter and water-retaining agent. The preparation method of the intermediate nutrient layer is as follows: first, part of the phosphogypsum, filler and organic matter are mixed in a ratio of 1:0 to 0.1:0.3, an appropriate amount of water is added to hydrate the gypsum, and after hydration is completed, the gypsum is crushed and granulated to form a 1 cm granular prefabricated material, and finally the prefabricated material, the remaining phosphogypsum and water-retaining agent are added in a ratio of 1:1 to 3:0.8 to 1, and then 0.3-5‰ of the retarder and water of the remaining phosphogypsum are added to a mixing equipment, the water-cement ratio is controlled to 0.4 to 0.5, and after uniform mixing, the gypsum is sprayed in layers to the surface of the bottom fixed layer to reach a set thickness. When the phosphogypsum contains anhydrous gypsum, the raw materials of the intermediate nutrient layer are composed of phosphogypsum, filler, retarder, organic matter, water-retaining agent, and activator. The preparation method of the intermediate nutrient layer is as follows: first, part of the phosphogypsum, filler, organic matter, and activator are mixed in proportion, an appropriate amount of water is added to hydrate the gypsum, and after hydration is completed, the gypsum is crushed and granulated to form a 1 cm granular prefabricated material, wherein the ratio of phosphogypsum, filler, and organic matter is 1:0-0.1:0.3, and the activator is added at 1-5% of the weight of the anhydrous gypsum; finally, the prefabricated material, the remaining phosphogypsum, and water-retaining agent are added at a ratio of 1:1-3:0.8-1, and 0.3-5‰ of the weight of the remaining phosphogypsum retarder and water are added to a mixing equipment, the water-cement ratio is controlled to 0.4-0.5, and after uniform mixing, the material is sprayed in layers to the surface of the bottom fixed layer to reach a set thickness. The filler is one or more of mountain sand, river sand, machine-made sand and clay; the organic matter is one or more of matrix soil, peat soil, livestock manure, humus soil, sludge, lake sludge and microbial agent; the sludge is one or more of municipal sludge and domestic sewage sludge; the water-retaining agent is one or more of biochar, grass fiber, wood fiber, perlite, vitrified microbeads, biological starch water-retaining agent, resin water-retaining agent, vermiculite, coal slag, ceramsite and volcanic rock particles; When the phosphogypsum does not contain anhydrous gypsum, the raw materials of the upper planting layer are composed of phosphogypsum, filler, retarder, organic matter, water-retaining agent and plant seeds; the preparation method of the upper planting layer is to first mix part of the phosphogypsum, filler and organic matter in a ratio of 1:0.2-0.5:0.6-1, add an appropriate amount of water to hydrate the gypsum, crush it after hydration is completed, and granulate it to form a 1 cm granular prefabricated material, finally, the prefabricated material, the remaining phosphogypsum, the water-retaining agent in a ratio of 1:0.5-2:1, and then add 0.3-5‰ of the retarder of the remaining phosphogypsum and water to a stirring device, control the water-cement ratio to 0.4-0.6, add plant seeds during stirring, stir evenly, and then spray the material in layers to the surface of the middle nutrient layer to a predetermined thickness; When the phosphogypsum contains anhydrous gypsum, the raw materials of the upper planting layer are composed of phosphogypsum, filler, retarder, organic matter, water-retaining agent, plant seeds, and stimulant. The preparation method of the upper planting layer is as follows: first, part of the phosphogypsum, filler, organic matter, and stimulant are mixed in proportion, an appropriate amount of water is added to hydrate the gypsum, and after hydration is completed, the gypsum is crushed and granulated to form a 1 cm granular prefabricated material, wherein the ratio of phosphogypsum, filler, and organic matter is 1:0.2-0.5:0.6-1, and the stimulant is added at 1-5% of the mass of the anhydrous gypsum; finally, the prefabricated material, the remaining phosphogypsum, and water-retaining agent are added at a ratio of 1:0.5-2:1, and 0.3-5‰ of the retarder and water of the remaining phosphogypsum are added to a stirring device to control the water-cement ratio to 0.4-0.6, and plant seeds are added during stirring. After stirring, the mixture is evenly stirred and sprayed in layers until the surface of the middle nutrient layer reaches a predetermined thickness. The mass of the plant seeds is 1 to 3‰ of the total mass of the upper planting layer material; the filler is one or more of mountain sand, river sand, machine-made sand and clay; the organic matter is one or more of matrix soil, peat soil, livestock manure, humus soil, sludge, lake bottom silt, and microbial agents, and the sludge is one or more of municipal sludge and domestic sludge; the water-retaining agent is one or more of biochar, grass fiber, wood fiber, perlite, glass beads, biological starch water-retaining agent, resin water-retaining agent, vermiculite, coal furnace slag, expanded clay and volcanic rock particles.

2. A novel four-layer phosphogypsum-based high and steep slope greening spraying material according to claim 1, characterized in that: The bonding strength of the final cementitious product formed by the hydration process of the phosphogypsum is anhydrous gypsum>complex gypsum>hemihydrate gypsum; the phosphogypsum-based high and steep slope greening spraying material contains a gypsum retarder.

3. The novel four-layer phosphogypsum-based high and steep slope greening spraying material according to claim 1, characterized in that: The mass proportions of phosphogypsum in the bottom fixing layer, middle nutrient layer, upper planting layer and surface maintenance layer are 85-99%, 60-75%, 30-60% and 7-15% respectively.

4. The novel four-layer phosphogypsum-based high and steep slope greening spraying material according to claim 1, characterized in that: The particle size must be controlled below 1 cm before feeding and mixing; during spraying construction, it is necessary to wait until the underlying structure has initially solidified before proceeding.