Method for preparing slow-release phosphate fertilizer soil from graphite tailing sand and coal gangue and application of slow-release phosphate fertilizer soil

Abstract

The invention discloses a method for preparing slow-release phosphate fertilizer soil from graphite tailing sand and coal gangue and application, and relates to the technical field of solid waste resource utilization and agricultural fertilizer. The slow-release phosphate fertilizer soil is prepared by carrying out gradient magnetic separation-acid leaching synergistic pretreatment on graphite tailing sand (the removal rate of magnetic impurities reaches 92%-95%), carrying out segmented roasting-microwave activation treatment on coal gangue (the specific surface area is increased to 28.6-32.4 m < 2 > / g), then mixing the pretreated raw materials with a composite exciting agent, and carrying out a low-temperature sintering-granulation molding process. The problem of low resource utilization rate of the graphite tailing sand and the coal gangue is effectively solved, the soil phosphorus slow release period of the prepared phosphate fertilizer reaches 120-150 days, the prepared phosphate fertilizer can meet the nutrient requirement of phosphorus-loving crops in the whole growth period, compared with a traditional phosphate fertilizer, the usage amount is reduced by 30-40%, the phosphorus utilization rate is increased to 65-72%, and remarkable economic, environmental and social benefits are achieved.

Description

Technical Field

[0001] This invention relates to the fields of solid waste resource utilization and agricultural fertilizer technology, specifically to a method and application for preparing slow-release phosphate fertilizer soil using graphite tailings sand and coal gangue. Background Technology

[0002] With the large-scale mining of graphite and coal resources, a large amount of graphite tailings and coal gangue have been generated. Statistics show that my country's graphite tailings stockpile exceeds 500 million tons, with a resource utilization rate of less than 8%; coal gangue stockpile exceeds 7 billion tons, with a comprehensive utilization rate of only 35%. These solid wastes not only occupy a large amount of land resources but also pollute soil and water bodies through leaching and dust, causing serious environmental problems. Meanwhile, the demand for phosphate fertilizers in agricultural production is increasing. Traditional phosphate fertilizers (such as superphosphate) are mostly fast-acting, resulting in rapid nutrient loss (leaching loss rate of 40%-50%), low utilization rate (only 10%-25%), and excessive use leading to soil compaction (increasing soil bulk density by 0.15-0.25 g / cm³). 3 Issues such as...

[0003] While there are existing studies on fertilizer preparation using solid waste, they suffer from numerous quantitative deficiencies. For example, patent CN108586442A uses steel slag and coal gangue to prepare compound fertilizer, requiring high-temperature calcination (1200-1300℃) and energy consumption as high as 850-920 kW·h / t, and does not involve the utilization of graphite tailings. Patent CN110255043A uses graphite tailings to prepare soil conditioner, which can only increase soil organic matter by 0.2-0.3 percentage points and does not achieve effective phosphorus supply (product total phosphorus content <2%). In addition, existing phosphate fertilizer preparation technologies mostly rely on a single raw material to stimulate phosphorus release, with a phosphorus slow-release period of only 30-60 days, which cannot meet the needs of phosphorus-loving crops (such as rapeseed, which requires phosphorus for about 120 days throughout its entire growth period). Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a method and application for preparing slow-release phosphate fertilizer soil using graphite tailings sand and coal gangue.

[0005] This invention proposes a novel technical solution that, through the synergistic pretreatment of graphite tailings sand and coal gangue, combined with a composite activation system, prepares phosphate fertilizer soil with slow-release properties under low-temperature conditions. This not only solves the problem of solid waste pollution but also reduces the amount of phosphate fertilizer used, filling a gap in existing technologies.

[0006] The core of this invention lies in achieving efficient activation and slow-release regulation of potential phosphorus in graphite tailings sand and coal gangue through a unique raw material pretreatment process and a composite activation system. Specifically, this invention is a method for preparing slow-release phosphate fertilizer soil using graphite tailings sand and coal gangue, which is carried out according to the following steps:

[0007] I. Pretreatment of graphite tailings:

[0008] The graphite tailings sand is crushed to a particle size of ≤2mm, and then subjected to gradient magnetic separation. The magnetic field strength in the first stage is 800~1000Gs, and the magnetic field strength in the second stage is 1500~1800Gs to remove magnetic impurities. Then, dilute sulfuric acid solution is added according to a certain liquid-solid ratio, heated and stirred, filtered, washed with water until neutral, and dried to obtain pretreated graphite tailings sand.

[0009] II. Coal gangue pretreatment:

[0010] The coal gangue was crushed to a particle size of ≤3mm, then roasted at 400~500℃ to remove organic matter; then activated under microwave power of 600~800W, cooled, and sodium carbonate solution was added at a certain liquid-solid ratio. The mixture was stirred at room temperature, filtered, and dried to obtain pretreated coal gangue.

[0011] III. Preparation of composite activators:

[0012] Phosphate rock powder, potassium sulfate, and humic acid are mixed to obtain a mixture; water accounting for 10% to 15% of the total mass of the mixture is added to the mixture and stirred until it becomes a paste. Then, it is aged at 30 to 40°C to obtain a composite activator.

[0013] IV. Mixed Molding:

[0014] Pretreated graphite tailings sand, pretreated coal gangue, and composite activator are mixed and fed into a twin-screw extruder. The mixture is extruded and granulated at a melting temperature of 120~150℃ and a rotation speed of 80~100r / min. The particle size is controlled and then dried to obtain slow-release phosphate fertilizer soil.

[0015] Application of a slow-release phosphate fertilizer soil in the cultivation of phosphorus-loving crops; the phosphorus-loving crops include rapeseed, cotton, and tomato; the application rate is 200-300 kg per acre, and it needs to be used in conjunction with 10-15% organic fertilizer.

[0016] The innovation of this invention:

[0017] I. Innovation in Raw Material Pretreatment Processes:

[0018] ① Gradient magnetic separation-acid leaching synergistic process: Compared with existing single magnetic separation (impurity removal rate is only 50%~60%) or single acid leaching (specific surface area increase is less than 10m²), 2The pretreated graphite tailings sand produced by this invention, processed using the / g) process, achieves a magnetic impurity removal rate of 92%~95% and increases the specific surface area to 18.3~22.5m². 2 / g, the phosphorus adsorption capacity is increased by 2.3 to 2.8 times. This pretreatment combination process has not been reported in existing patents.

[0019] ② Segmented calcination-microwave activation process: Compared with the existing single calcination process (which increases the specific surface area by less than 15m²), 2 Using either microwave treatment ( / g) or a single microwave treatment process (organic matter removal rate <70%), the organic matter removal rate of the pretreated coal gangue according to this invention reaches 90%~95%, and the specific surface area is increased to 28.6~32.4m². 2 / g, the dissolution rate of aluminum and silicon elements is increased by 30%~40%, which provides key conditions for the stable binding of phosphorus;

[0020] II. Innovation of Composite Excitation Systems:

[0021] Synergistic advantages of components: This invention is the first to use a composite activator of phosphate rock powder, potassium sulfate, and humic acid. Compared with existing single phosphate rock powder activators (phosphorus slow-release period of 30-60 days and utilization rate of 30-40%), the phosphorus slow-release period of this invention is extended to 120-150 days and the utilization rate is increased to 65-72%. Compared with single humic acid activators (product total phosphorus content <3%), the total phosphorus content of this system reaches 8-12%, meeting the nutrient requirements of phosphorus-loving crops.

[0022] Enhanced aging process: The aging process of this invention at 30~40℃ for 8~10h improves the stability of the activator system by 40~50%, and controls the fluctuation of phosphorus release within ±5%, which solves the problem of unstable phosphorus release in the prior art (the release fluctuation of the prior art is mostly ±15~20%).

[0023] III. Innovation in Low-Temperature Molding Processes:

[0024] Advantages in energy consumption and phosphorus retention: Utilizing low-temperature extrusion granulation at 120~150℃, compared to the existing high-temperature calcination process (1200~1300℃, energy consumption 850~920kW·h / t), this process consumes only 280~350kW·h / t, a reduction of 60~68%; the phosphorus retention rate reaches 90~93%, an improvement of 20~25% compared to the high-temperature process (phosphorus retention rate 65~75%).

[0025] Product physical properties optimized: Particle size 3~5mm, compressive strength 15~20N / particle. Compared with existing powder or small particle products (compressive strength <8N / particle), this product has a 60~70% higher breakage rate and a loss rate of less than 5% when applied mechanically (the loss rate of existing products is 15~20%).

[0026] The beneficial effects of this invention are:

[0027] This invention, through technological innovation, achieves synergy between solid waste resource utilization, agricultural cost reduction and efficiency improvement, and ecological environmental protection. Its specific beneficial effects are quantified from the following four dimensions:

[0028] (a) Resource utilization benefits of solid waste:

[0029] Disposal capacity: Each ton of product can dispose of 0.4 tons of graphite tailings and 0.3 tons of coal gangue. Based on an annual production of 100,000 tons of product, this can reduce the stockpiling of graphite tailings by 40,000 tons and coal gangue by 30,000 tons annually, saving approximately 12 mu of land (calculated based on a stockpiling height of 3m and a volume ratio of 0.8).

[0030] Resource efficiency: After pretreatment, the utilization rate of graphite tailings sand has increased from less than 8% on average in the industry to over 95%; the utilization rate of coal gangue has increased from 35% on average in the industry to over 90%, solving the industry pain point of "tailings storage - land pollution".

[0031] Emission reduction effect: During the traditional storage of coal gangue, approximately 15 million cubic meters of methane (a greenhouse gas) are released annually. 3 This invention utilizes coal gangue resources, reducing methane emissions by 15m³ per ton. 3 A production capacity of 100,000 tons can reduce methane emissions by 450,000 m³ per year. 3 This is equivalent to reducing CO2 emissions by 1,125 tons (based on the fact that the greenhouse effect of methane is 25 times that of CO2).

[0032] (II) Agricultural production efficiency

[0033] Fertilizer saving and yield increase: Compared with traditional phosphate fertilizer, the product of this invention reduces the amount of phosphate fertilizer used by 30%-40% (saving 15-20 kg of fertilizer per mu), and increases the yield of phosphorus-loving crops by 15%-25% (67.6 kg more cotton per mu and 820.1 kg more tomatoes per mu). Based on a net profit of 500 yuan for cotton and 3,000 yuan for tomatoes per mu, the income per mu can be increased by 75-750 yuan.

[0034] Soil quality improvement: After two years of continuous application, the soil organic matter content increased from 1.25%-1.26% to 2.1%-2.3%, and the soil bulk density increased from 1.43-1.45 g / cm³. 3 Reduced to 1.28-1.30 g / cm³ 3 The soil's physical and chemical properties have been continuously improved, forming a virtuous cycle of "fertilization-quality improvement-yield increase" and avoiding the soil compaction problem caused by traditional fertilization.

[0035] Stress resistance and loss reduction: Under adverse conditions such as drought and salinity, crop survival rate is increased by 23%-27%, and yield loss caused by adverse conditions is reduced by more than 30%, making it especially suitable for promotion and application in arid and semi-arid regions such as Northwest and North my country.

[0036] (III) Economic Cost-Benefit Analysis:

[0037] Raw material costs: Graphite tailings and coal gangue are both industrial wastes, with a purchase cost of only 20-30 yuan / ton (the purchase cost of phosphate rock powder, the raw material for traditional phosphate fertilizer, is 800-1000 yuan / ton). The raw material cost is 40%-50% lower than that of traditional phosphate fertilizer (the raw material cost per ton of product is reduced by 320-485 yuan).

[0038] Energy consumption cost: The energy consumption of the low-temperature forming process is 280-350 kWh / t, which is 60%-68% lower than that of the traditional high-temperature calcination process (850-920 kWh / t). Based on the industrial electricity price of 0.6 yuan / kWh, the energy consumption cost per ton of product is reduced by 342-372 yuan.

[0039] Overall Cost and Selling Price: The overall production cost of the product of this invention is about 800-1000 yuan / ton, which is lower than that of commercially available slow-release phosphate fertilizer (1500-2000 yuan / ton). The selling price can be set at 1200-1500 yuan / ton, which combines cost advantage and profit margin, making it highly competitive in the market.

[0040] (iv) Social promotion benefits:

[0041] Job creation: A production base with a capacity of 100,000 tons can create 150-200 jobs (covering raw material transportation, production operation, field technical services, etc.), of which 30% are technical positions, which can cultivate compound technical talents who combine solid waste resource utilization and agricultural fertilizer.

[0042] Technical Demonstration: This invention constructs a cross-border integrated technology model of "industrial solid waste-agricultural fertilizer-soil improvement", which provides a reference for the agricultural resource utilization of other solid wastes (such as steel slag and fly ash). It is expected to drive the promotion and application of related technologies and form a market of hundreds of billions of yuan for agricultural utilization of solid waste. Detailed Implementation

[0044] Specific Implementation Method 1: This implementation method is a method for preparing slow-release phosphate fertilizer soil using graphite tailings sand and coal gangue, specifically completed according to the following steps:

[0045] I. Pretreatment of graphite tailings:

[0046] Graphite tailings sand is crushed to a particle size ≤2mm, and then subjected to gradient magnetic separation. The first stage uses a magnetic field strength of 800~1000Gs, which can remove 60~70% of strongly magnetic impurities (such as magnetite); the second stage uses a magnetic field strength of 1500~1800Gs, which can remove 92~95% of weakly magnetic impurities (such as hematite), avoiding interference from impurities on phosphorus release (experiments show that when the magnetic impurity content is >3%, the phosphorus release rate decreases by 15~20%). Then, dilute sulfuric acid solution is added according to a certain liquid-solid ratio, and the mixture is heated and stirred (under these conditions, 45~55% of the calcium, magnesium and other minerals (mainly CaCO3 and MgCO3) in the tailings sand can be dissolved, increasing the specific surface area of ​​the tailings sand from the initial 5.2~6.8m²). 2 / g increased to 18.3~22.5m 2 / g, forming a porous structure with a pore size of 2~50nm, providing sufficient sites for phosphorus adsorption (for every 1% increase in porosity, the amount of phosphorus adsorption increases by 0.8~1.2mg / g)), filtered, washed with water until neutral, dried, to obtain pretreated graphite tailings sand;

[0047] II. Coal gangue pretreatment:

[0048] The coal gangue is crushed to a particle size ≤3mm, and then roasted at 400~500℃ to remove 90~95% of the organic matter (the initial organic matter content of the coal gangue is 8~12%). It is then activated by microwave treatment at a power of 600~800W (microwave energy can induce thermal stress inside the coal gangue, forming numerous microcracks, increasing the specific surface area from the initial 8.5~10.2m²). 2 / g increased to 28.6~32.4m 2 / g, the number of active sites increases by 2.5 to 3 times), after cooling, add sodium carbonate solution according to a certain liquid-solid ratio, stir at room temperature (this can increase the dissolution rate of aluminum and silicon elements in coal gangue by 35 to 42% and 28 to 35% respectively. These elements can form stable aluminum phosphate (AlPO4) and silicon phosphate (Si3(PO4)4) compounds with phosphorus in the composite activator. The dissolution rate of such compounds in soil is only 1 / 5 to 1 / 3 of that of traditional calcium phosphate, realizing the slow release of phosphorus), filter, dry, and obtain pretreated coal gangue;

[0049] III. Preparation of composite activators:

[0050] Phosphate rock powder (P2O5 content ≥30%), potassium sulfate, and humic acid (organic matter content ≥70%) are mixed to obtain a mixture. The phosphate rock powder provides the basic phosphorus source (accounting for 75-80% of the total phosphorus content), while potassium sulfate not only supplements potassium (the product has a K2O content of 3-5%) but also promotes the dissolution of phosphorus from the phosphate rock powder (experiments show that when the potassium sulfate addition is 40% of the phosphate rock powder mass, the phosphorus dissolution rate increases by 22-28%). Humic acid can adsorb phosphorus through functional groups such as carboxyl and hydroxyl groups (adsorption capacity reaches 15-18 mg). / g), while regulating the soil microbial environment (the number of beneficial soil bacteria increases by 1.8-2.2 times after application); add 10%~15% water to the mixture, stir until it becomes a paste, and then age it at 30~40℃ (this process allows the components to fully react and form a stable colloidal system; if the aging time is less than 6 hours, the system stability is poor, and the phosphorus release fluctuation range reaches ±15%; if the aging time exceeds 12 hours, some phosphorus will be fixed, and the release rate will decrease by 8%-12%), to obtain the composite activator;

[0051] IV. Mixed Molding:

[0052] Pretreated graphite tailings sand, pretreated coal gangue, and composite activator are mixed and fed into a twin-screw extruder. The mixture is extruded and granulated at a melting temperature of 120-150℃ (at which temperature the phosphorus volatilization loss rate is only 2-3%, compared to calcination at 800℃, the loss rate is reduced by 25-30%, and the phosphorus retention rate reaches 90-93%) and a rotation speed of 80-100 r / min. The particle size is controlled (3-5 mm to maintain a porosity of 35-40%), further regulating the phosphorus release rate (if the particle size is <2 mm, the initial release rate is too high; if the particle size is >6 mm, the later release is insufficient). The mixture is then dried to obtain slow-release phosphate fertilizer soil (moisture content controlled at 8-12%; if the moisture content is <8%, the particles are easily broken; if the moisture content is >12%, they are easily agglomerated).

[0053] In step one of this embodiment, the gradient magnetic separation uses a counter-current two-stage magnetic separator (model CXJ-2000) equipped with an adjustable magnetic field coil. The magnetic field strength is 800~1000Gs in the first stage and 1500~1800Gs in the second stage. The magnetic separator has a processing capacity of 10~15 tons / hour, ensuring that the tailings sand stays in the magnetic separator for 15~20 minutes in each stage (adjusted by the conveyor belt speed of 1.2-1.5m / min).

[0054] Key points of operation: Before magnetic separation, the moisture content of graphite tailings sand should be controlled at 15~20% (too high moisture content will easily cause agglomeration, and too low moisture content will easily cause dust). After magnetic separation, a vibrating screen (2mm aperture) should be used to screen and remove large unbroken particles to avoid insufficient acid leaching in the subsequent process.

[0055] In step two of this embodiment, microwave activation is performed using a continuous microwave reactor (model MW-600C) with a microwave frequency of 2450MHz, a power of 600~800W, a reaction chamber length of 3m, and the material is conveyed by a conveyor belt (speed 0.5~0.8m / min) to ensure an activation time of 15-20min.

[0056] Key points of operation: Before microwave activation, the moisture content of the roasted coal gangue should be reduced to below 5% (too high moisture content will cause microwave energy to be absorbed by the moisture, reducing activation efficiency). During the activation process, the material temperature should be monitored in real time (controlled at 180~220℃ to avoid the coal gangue from sintering due to excessive temperature).

[0057] In step three of this embodiment, the twin-screw extrusion granulation uses a conical twin-screw extruder (model SHJ-65) with a screw diameter of 65mm, a length-to-diameter ratio of 32:1, and a die orifice diameter of 3-5mm (which can be replaced). The heating section is divided into three zones (zone 1: 100-110℃, zone 2: 120-150℃, and zone 3: 120-140℃) to ensure that the material is preheated, melted, and shaped in different zones.

[0058] Key points of operation: The moisture content of the mixture should be controlled between 18% and 22% (too low moisture content will lead to difficulty in extrusion and rough particle surface; too high moisture content will easily cause particle sticking). After extrusion, use a pelletizer (speed 300-500r / min) to cut the particles to ensure that the particle length to particle size ratio is 1:1-1.5:1, which is conducive to uniform drying.

[0059] Specifications for the storage and application of slow-release phosphate fertilizer prepared in this invention in soil:

[0060] Storage requirements: The product should be stored in a well-ventilated and dry warehouse, with a stacking height not exceeding 8m (to avoid crushing of the bottom particles). It should be kept away from moisture and acidic substances (to prevent moisture absorption and clumping or phosphorus loss). The storage period can reach 12 months (after 6 months of storage, the effective phosphorus content will only decrease by 2.3%-3.5%, still meeting the usage requirements).

[0061] Application method:

[0062] Base application: 7-10 days before sowing phosphorus-loving crops, spread the product evenly on the soil surface and plow to a depth of 20-30cm to ensure the product is fully mixed with the soil. The application rate is 200-300 kg per acre (200-250 kg for clay soil, 250-300 kg for sandy soil; sandy soil has a weak fertilizer retention capacity, so the application rate needs to be increased appropriately).

[0063] Combined application: Use with 10%-15% organic fertilizer (such as well-rotted straw or sheep manure). The combination of organic fertilizer and the product of this invention can further enhance soil microbial activity and increase phosphorus utilization by another 5%-8%.

[0064] Contraindications and precautions for use:

[0065] 1. Avoid direct mixing or simultaneous application with alkaline substances. Specific requirements and reasons are as follows:

[0066] (1) Core Contraindication: The available phosphorus in the product of this invention mainly exists in the form of monocalcium phosphate, aluminum phosphate, silicon phosphate, etc. In an alkaline environment (pH>7.5), these substances are easily combined with calcium and magnesium ions in the soil or alkaline substances to form insoluble calcium phosphate and magnesium phosphate precipitates, which fix the available phosphorus and prevent crops from absorbing and utilizing it, directly reducing fertilizer efficiency. Experimental data show that when the soil pH≥8.0, if it is mixed with alkaline substances, the utilization rate of available phosphorus in the product will drop sharply from 65%-72% to 30%-35%, and the fertilizer efficiency will be lost by more than half. At the same time, alkaline substances will also destroy the humic acid structure in the product, causing its function of adsorbing phosphorus and regulating soil microorganisms to fail, further affecting the soil improvement effect.

[0067] (2) Specific categories of alkaline substances that are contraindicated:

[0068] ① Alkaline fertilizers: including quicklime, slaked lime, wood ash, ammonium bicarbonate, ammonia water, calcium magnesium phosphate fertilizer (alkaline type), etc. When these fertilizers are mixed with this product, they will rapidly increase the local soil pH value and trigger phosphorus fixation reaction in a short time. Among them, the effect of strong alkaline fertilizers such as quicklime and slaked lime is the most significant. Within 12 hours after mixing, it can cause the loss of more than 40% of effective phosphorus.

[0069] ② Alkaline soil conditioners: such as desulfurized gypsum (high alkalinity type), shell powder (uncomposted), alkaline slag, etc. These substances are used to adjust acidic soil. If they are applied at the same time as this product, they will excessively increase the soil alkalinity, especially in neutral or weakly alkaline soils, which can easily lead to excessive soil pH, not only reducing fertilizer efficiency, but also affecting crop root growth.

[0070] ③ Other alkaline substances: such as industrial waste alkali, alkaline pesticides (such as Bordeaux mixture, lime sulfur, etc.). These substances not only reduce fertilizer efficiency, but some may also react chemically with the ingredients in the product to produce harmful substances, or affect the efficacy of pesticides and increase the risk of pesticide damage to crops.

[0071] (3) Application interval and avoidance recommendations:

[0072] ① Interval: If the above-mentioned alkaline substances need to be applied, an interval of at least 15-20 days should be maintained between them and this product. Among them, it is recommended to wait more than 20 days for strong alkaline substances such as quicklime and slaked lime, so as to allow them to fully react in the soil and the pH value to stabilize before applying this product; it is recommended to wait more than 15 days for weak alkaline fertilizers such as wood ash and ammonium bicarbonate to reduce mutual interference.

[0073] ② Application sequence: Apply this product first and mix it thoroughly with deep plowing. After it has fully integrated with the soil for 7-10 days and the nutrients have initially stabilized, apply an appropriate amount of alkaline substance according to the soil pH value; or apply alkaline substance first to adjust the soil pH to 7.0-7.5, and then apply this product after an interval of 20 days to ensure that the soil pH value is within the appropriate range and maximize fertilizer efficiency.

[0074] ③ Application in zones: If two substances need to be applied to the same plot of land at the same time due to soil improvement needs, they should be applied in zones or holes to avoid direct contact between the two. The distance between them should be at least 20-30cm. After application, cover the soil and water in time to reduce the local alkalinity concentration.

[0075] (4) Handling of abnormal situations: If this product is accidentally mixed with alkaline substances or applied at the same time, the following measures should be taken in time:

[0076] ① Light mixing (mixing ratio < 1:5): Immediately increase soil irrigation, watering 30-50m³ per acre. This will dilute the concentration of alkaline substances in the soil, reduce the phosphorus fixation rate, and promote the slow release of phosphorus precipitated in the soil.

[0077] ② Heavy mixing (mixing ratio ≥ 1:5): In addition to sufficient irrigation, apply 50-80 kg of well-rotted organic fertilizer or 10-15 kg of humic acid per mu (0.067 hectares) to adjust soil pH using the buffering effect of organic fertilizer and humic acid, while replenishing the damaged microbial community and reducing fertilizer loss; if the soil pH is > 8.5, apply an additional 5-8 kg / mu of ferrous sulfate (acidity regulator) to adjust the soil pH to the range of 7.0-7.5.

[0078] ③ Follow-up monitoring: Test the soil pH and crop growth status 7 days and 15 days after application. If the crop shows symptoms of phosphorus deficiency such as yellowing leaves and slow growth, a 0.2%-0.3% potassium dihydrogen phosphate solution can be sprayed on the leaves 2-3 times in a row, with an interval of 7 days between each spray, to quickly replenish available phosphorus and alleviate the symptoms of nutrient deficiency.

[0079] 2. Other precautions:

[0080] (1) Deep plowing in time after application: Ensure that the product is mixed evenly with the soil to avoid it being washed away by rain or blown away by the wind after being spread on the surface, which would affect the fertilizer effect;

[0081] (2) Storage conditions: The product should be stored in a well-ventilated and dry warehouse, avoiding moisture and rain. The stacking height should not exceed 8m to prevent the bottom particles from being crushed by pressure.

[0082] (3) Applicable crops: It is mainly applicable to phosphorus-loving crops such as cotton, tomatoes, rapeseed, and cucumbers. It is not applicable to crops with poor phosphorus tolerance (such as buckwheat and potatoes). When applying to such crops, the dosage should be reduced by more than 30%, and a small-scale test should be conducted in advance.

[0083] (4) Application period: Only for basal application, not for topdressing. If phosphorus deficiency symptoms appear in the middle of crop growth, it can be combined with fast-acting phosphate fertilizer for foliar spraying to avoid direct topdressing of this product.

[0084] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the mass fraction of the dilute sulfuric acid solution mentioned in step one is 5-8%; the liquid-to-solid ratio mentioned in step one is (3-5):1. Other steps are the same as in Specific Implementation Method One.

[0085] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One or Two in that: the heating and stirring temperature in step one is 50~60℃, and the heating and stirring time is 2~3 hours; the gradient magnetic separation in step one uses a counter-current magnetic separator, and the magnetic separation time for each stage is 15~20 minutes. Other steps are the same as in Specific Implementation Method One or Two.

[0086] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in the following ways: In step two, the material is calcined at 400-500℃ for 1.5-2 hours; the activation treatment in step two is performed using a continuous microwave reactor, with the material residence time controlled by the conveyor belt speed, and the activation treatment time is 15-20 minutes; the mass fraction of the sodium carbonate solution in step two is 3-5%. Other steps are the same as in Specific Implementation Methods One to Three.

[0087] Specific Implementation Method Five: This implementation method differs from Specific Implementation Methods One to Four in that: the liquid-to-solid ratio in step two is (2~3):1; the stirring time at room temperature in step two is 1~1.5h; and the calcination in step two is carried out in a rotary kiln with a heating rate of 5~8℃ / min. Other steps are the same as in Specific Implementation Methods One to Four.

[0088] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in the following ways: the particle size of the phosphate rock powder in step three is ≤100 mesh; the mass ratio of phosphate rock powder, potassium sulfate, and humic acid in step three is 5:2:3; the aging time at 30~40℃ in step three is 8~10 hours; the P2O5 content in the phosphate rock powder in step three is ≥30%; and the humic acid in step three is weathered coal humic acid with an organic matter content ≥70%. Other steps are the same as in Specific Implementation Methods One to Five.

[0089] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods One through Six in that the mass ratio of pretreated graphite tailings sand, pretreated coal gangue, and composite activator in step four is 4:3:3; and the particle size is controlled to be 3-5 mm in step four. Other steps are the same as in Specific Implementation Methods One through Six.

[0090] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Methods One to Seven in that: the drying temperature in step four is 80~100℃, and the drying time is 2~3 hours; the moisture content of the slow-release phosphate fertilizer soil in step four is controlled at 8~12%, and the compressive strength is ≥15N / particle. Other steps are the same as in Specific Implementation Methods One to Seven.

[0091] Specific Implementation Method Nine: This implementation method is a slow-release phosphate fertilizer soil, which is prepared according to any one of Specific Implementation Methods One to Eight.

[0092] Specific Implementation Method 10: This implementation method is an application of slow-release phosphate fertilizer soil in the planting of phosphorus-loving crops; the phosphorus-loving crops include rapeseed, cotton, and tomato; the application rate is 200-300 kg per acre, and it needs to be used in conjunction with 10-15% organic fertilizer.

[0093] The beneficial effects of the present invention are verified using the following embodiments:

[0094] Example 1: A method for preparing slow-release phosphate fertilizer soil using graphite tailings sand and coal gangue, characterized in that the method is specifically carried out according to the following steps:

[0095] I. Pretreatment of graphite tailings:

[0096] The graphite tailings sand (initial magnetic impurity content 5.8%, specific surface area 6.2 m²) 2 The graphite tailings (g) were crushed to a particle size of 1.5 mm, and then subjected to gradient magnetic separation. The first stage involved magnetic separation at a magnetic field strength of 900 Gs for 18 min, and the second stage at a magnetic field strength of 1600 Gs for 18 min to remove magnetic impurities, achieving a removal rate of 94.1%. A 7% (w / w) dilute sulfuric acid solution was then added at a liquid-to-solid ratio of 4:1, and the mixture was stirred and leached at 55°C for 2.5 h. The mixture was then filtered, washed with water until neutral, and dried to obtain pretreated graphite tailings sand (with a surface area of ​​20.7 m²). 2 / g, calcium and magnesium removal rate 51.3%).

[0097] The gradient magnetic separation mentioned in step one uses a counter-current magnetic separator;

[0098] II. Coal gangue pretreatment:

[0099] Coal gangue (initial organic matter content 10.5%, specific surface area 9.8 m²)2 / g) was crushed to a particle size of 2mm, heated to 450℃ at 6℃ / min in a rotary kiln, and calcined for 1.8h to remove organic matter, with an organic matter removal rate of 92.3%; then activated in a microwave reactor with a microwave power of 800W for 18min, cooled, and then a 4% sodium carbonate solution was added at a liquid-to-solid ratio of 2.5:1. The mixture was stirred at room temperature for 1.2h, filtered, and dried at 90℃ to obtain pretreated coal gangue (with a surface area of ​​30.2m²). 2 / g, aluminum dissolution rate 38.7%, silicon dissolution rate 32.5%).

[0100] III. Preparation of composite activators:

[0101] Phosphate rock powder (P2O5 content 32%), potassium sulfate, and humic acid (organic matter content 75%) were mixed in a mass ratio of 5:2:3 to obtain a mixture. Water accounting for 12% of the total mass of the mixture was added to the mixture and stirred until it became a paste. The mixture was then aged at 35°C for 9 hours to obtain a composite activator (the stability of the activator system reached 96.2%, and there was no stratification in the centrifugation test).

[0102] The particle size of the phosphate rock powder mentioned in step three is ≤100 mesh;

[0103] The humic acid mentioned in step three is weathered coal humic acid;

[0104] IV. Mixed Molding:

[0105] Pretreated graphite tailings sand, pretreated coal gangue, and composite activator were mixed in a mass ratio of 4:3:3 and fed into a twin-screw extruder. The mixture was extruded and granulated at a melting temperature of 135℃ and a rotation speed of 90 r / min, with the particle size controlled at 4 mm. The mixture was then dried at 90℃ for 2.5 h to obtain slow-release phosphate fertilizer soil (the slow-release phosphate fertilizer soil contains 10.3% total phosphorus and 4.2% K2O).

[0106] The moisture content of the soil containing the slow-release phosphate fertilizer described in step four is controlled at 10%, and the compressive strength is 18 N / particle.

[0107] Example 2: A method for preparing slow-release phosphate fertilizer soil using graphite tailings sand and coal gangue, characterized in that the method is specifically carried out according to the following steps:

[0108] I. Pretreatment of graphite tailings:

[0109] The graphite tailings sand (initial magnetic impurity content 5.8%, specific surface area 6.2 m²) 2The material (g) was crushed to a particle size of 2 mm, and then subjected to gradient magnetic separation. The first stage involved magnetic separation at a magnetic field strength of 1000 Gs for 20 min, and the second stage at a magnetic field strength of 1800 Gs for 20 min to remove magnetic impurities, achieving a removal rate of 95.3%. Then, an 8% (w / w) dilute sulfuric acid solution was added at a liquid-to-solid ratio of 5:1, and the mixture was stirred and leached at 60℃ for 3 h. After filtration, washing with water until neutral, and drying, pretreated graphite tailings sand (with a surface area of ​​22.5 m²) was obtained. 2 / g, calcium and magnesium removal rate 54.8%).

[0110] The gradient magnetic separation mentioned in step one uses a counter-current magnetic separator;

[0111] II. Coal gangue pretreatment:

[0112] Coal gangue (initial organic matter content 10.5%, specific surface area 9.8 m²) 2 / g) was crushed to a particle size of 3mm, heated to 500℃ at 6℃ / min in a rotary kiln, and calcined for 2h to remove organic matter, with an organic matter removal rate of 94.7%; then activated in a microwave reactor with a microwave power of 800W for 20min, cooled, and then a 5% sodium carbonate solution was added at a liquid-to-solid ratio of 3:1. The mixture was stirred at room temperature for 1.5h, filtered, and dried at 90℃ to obtain pretreated coal gangue (with a surface area of ​​32.4m²). 2 / g, aluminum dissolution rate 41.8%, silicon dissolution rate 34.7%).

[0113] III. Preparation of composite activators:

[0114] Phosphate rock powder (P2O5 content 35%), potassium sulfate, and humic acid (organic matter content 78%) were mixed in a mass ratio of 5:2:3 to obtain a mixture. Water accounting for 15% of the total mass of the mixture was added to the mixture and stirred until it became a paste. The mixture was then aged at 40°C for 10 hours to obtain a composite activator (the stability of the activator system reached 97.5%, and no stratification was observed in the centrifugation test).

[0115] The particle size of the phosphate rock powder mentioned in step three is ≤100 mesh;

[0116] The humic acid mentioned in step three is weathered coal humic acid;

[0117] IV. Mixed Molding:

[0118] Pretreated graphite tailings sand, pretreated coal gangue, and composite activator were mixed in a mass ratio of 4:3:3 and fed into a twin-screw extruder. The mixture was extruded and granulated at a melting temperature of 150℃ and a rotation speed of 100r / min, with the particle size controlled at 5mm. The mixture was then dried at 100℃ for 3 hours to obtain slow-release phosphate fertilizer soil (the slow-release phosphate fertilizer soil contains 11.8% total phosphorus and 4.8% K2O).

[0119] The moisture content of the soil containing the slow-release phosphate fertilizer described in step four is controlled at 8%, and the compressive strength is 20 N / particle.

[0120] Application Examples (Cross-Crop Application Group):

[0121] Using the slow-release phosphate fertilizer soil prepared in Example 1, field trials were conducted in cotton and tomato fields, with three control groups: ① blank group (no phosphate fertilizer applied); ② traditional phosphate fertilizer group (superphosphate, 50 kg / mu, equivalent to 7.5 kg pure phosphorus); ③ the present invention group (250 kg / mu of slow-release phosphate fertilizer soil prepared in Example 1, equivalent to 25.75 kg pure phosphorus, combined with 12% organic fertilizer). The trial period was 120 days (the entire growth period of cotton) and 150 days (the entire growth period of tomato). The results are shown in Table 1.

[0122] Table 1

[0123]

[0124] Comparison with Example 1 (Gradient-free magnetic separation): The difference between this embodiment and Example 1 is that the gradient magnetic separation step for graphite tailings is omitted, i.e., in step one: the graphite tailings (initial magnetic impurity content 5.8%, specific surface area 6.2m²) are separated. 2 The powder was crushed to a particle size of 1.5 mm, and then a 7% dilute sulfuric acid solution was added at a liquid-to-solid ratio of 4:1. The mixture was stirred and leached at 55°C for 2.5 h, filtered, washed with water until neutral, and dried to obtain pretreated graphite tailings sand. Other processes and parameters were the same as in Example 1.

[0125] Compared with Example 1, the phosphorus release rate of Control Example 1 decreased by 18.7%, and the cotton yield decreased by 12.3%.

[0126] Comparative Example 2 (without microwave activation): The difference between this example and Example 1 is that the microwave activation step for coal gangue is omitted, i.e., in step two: the coal gangue (initial organic matter content 10.5%, specific surface area 9.8 m²) is... 2 The coal gangue (g) was crushed to a particle size of 2 mm and calcined in a rotary kiln at a rate of 6 °C / min to 450 °C for 1.8 h to remove organic matter, with an organic matter removal rate of 92.3%. Then, a 4% sodium carbonate solution was added at a liquid-to-solid ratio of 2.5:1, and the mixture was stirred at room temperature for 1.2 h. After filtration, the gangue was dried at 90 °C to obtain pretreated coal gangue. Other processes and parameters were the same as in Example 1.

[0127] In contrast, the specific surface area of ​​the coal gangue in Example 2 is only 15.6 m². 2 / g, the phosphorus slow-release period is shortened to 65 days, and phosphorus deficiency symptoms (leaves turn purple) appear in tomatoes in the later stage.

[0128] Comparative Example 3 (Single Activator): The difference between this example and Example 1 is that the composite activator uses only phosphate rock powder, that is, in step three: water accounting for 12% of the total mass of the mixture is added to the phosphate rock powder (P2O5 content is 32%), stirred until a paste is formed, and then aged at 35°C for 9 hours to obtain a single activator. Other processes and parameters are the same as in Example 1.

[0129] The total phosphorus content of the soil prepared with slow-release phosphate fertilizer in Example 3 was 8.5%, the available phosphorus content was 4.2% (available phosphorus conversion rate was 49.4%), the phosphorus slow-release period was only 58 days, and the cotton yield was 392.5 kg / mu (13.3% lower than Example 1), which proves the key role of potassium sulfate in promoting phosphorus dissolution and humic acid in regulating slow release.

[0130] Comparative Example 4 (High-Temperature Molding): In this example, high-temperature calcination at 800℃ replaces low-temperature extrusion at 135℃. Specifically, in step four: pretreated graphite tailings sand, pretreated coal gangue, and composite activator are mixed in a mass ratio of 4:3:3, calcined at 800℃ for 50 minutes, and cooled to room temperature to obtain slow-release phosphate fertilizer soil. Other processes and parameters are the same as in Example 1.

[0131] Compared with Example 4, the slow-release phosphate fertilizer prepared in soil had a phosphorus retention rate of only 72.3% (18% lower than Example 1), an energy consumption of 880 kW·h / t (214% higher than Example 1), and a particle compressive strength of 22 N / particle (although high, the energy consumption was too high), which proves the economic efficiency and phosphorus retention advantage of the low-temperature molding process.

[0132] Performance testing:

[0133] To comprehensively verify the performance of the slow-release phosphate fertilizer soil prepared according to this invention, the following six core performance tests were conducted using a combination of laboratory testing and field monitoring. The specific methods and results are as follows:

[0134] (a) Phosphorus sustained-release performance test:

[0135] Test method: Referring to the "Determination of Release Rate of Slow-Release Fertilizers" (GB / T23348-2022), the water extraction-molybdenum antimony colorimetric method was adopted. Under the condition of constant temperature water bath at 25℃, samples were taken at 1d, 7d, 15d, 30d, 60d, 90d, 120d, and 150d respectively to determine the phosphorus content in the leachate and calculate the cumulative release rate and release rate.

[0136] Test results:

[0137] The slow-release phosphate fertilizer soil prepared in Example 1 showed the following cumulative release rates: 8.2% at 1 day (slow initial release to avoid burning seedlings), 28.5% at 30 days, 45.3% at 60 days, 61.2% at 90 days, 72.6% at 120 days, and 78.3% at 150 days, with an average release rate of 0.52% / day. The release curve showed a trend of "slow rise - stable release" with no sudden release phenomenon.

[0138] The slow-release phosphate fertilizer soil prepared in Example 2 had a cumulative release rate of 7.8% in 1 day, 26.3% in 30 days, 43.1% in 60 days, 59.8% in 90 days, 70.5% in 120 days, and 76.8% in 150 days, with an average release rate of 0.51% / day. The release stability was better than that in Example 1.

[0139] Traditional superphosphate (control): 1-day cumulative release rate 35.6% (significant burst release), 30-day cumulative release rate 68.2%, 60-day cumulative release rate 85.3%, and almost no phosphorus release after 90 days, with an average release rate of 0.95% / day, which cannot meet the crop's needs in the later stages.

[0140] (II) Nutrient content and availability testing:

[0141] Test method:

[0142] Total phosphorus content: determined by sulfuric acid-perchloric acid digestion-molybdenum antimony colorimetric method;

[0143] Available phosphorus content: determined by 0.5 mol / L NaHCO3 extraction-molybdenum antimony colorimetric method;

[0144] Potassium content: determined by flame photometry;

[0145] Organic matter content: determined by potassium dichromate oxidation-external heating method.

[0146] The test results are shown in Table 2:

[0147] Table 2

[0148]

[0149] The results showed that the effective phosphorus content of the product of this invention was over 83%, which was higher than that of traditional superphosphate, and it also had the ability to supply potassium and organic matter. The effective phosphorus conversion rate of the control group was less than 50% due to the lack of synergistic effect of potassium sulfate and humic acid.

[0150] (III) Soil amendment performance test:

[0151] Test method: In barren soil (initial bulk density 1.45 g / cm³) 3In a soil with a porosity of 38% and a pH of 7.8, the product of Example 1 was applied at a rate of 250 kg per acre. After 90 days of cultivation, the soil bulk density, porosity, pH value, and number of microorganisms were measured.

[0152] Test results:

[0153] Soil bulk density: from 1.45 g / cm³ 3 Reduced to 1.32 g / cm³ 3 The soil porosity decreased by 8.9%;

[0154] Porosity increased from 38% to 45%, an increase of 7 percentage points, which is beneficial to root aeration and water penetration;

[0155] pH value: adjusted from 7.8 to 7.3, tending towards neutrality, improving the saline-alkali soil environment;

[0156] Microbial count: Bacterial count from 1.2 × 10⁻⁶ 8 CFU / g increased to 3.5×10 8 CFU / g, fungal count from 2.5 × 10 5 CFU / g increased to 6.8×10 5 CFU / g, actinomycete count from 3.8 × 10 6 CFU / g increased to 9.2×10 6 CFU / g significantly enhanced soil microbial activity.

[0157] (iv) Stress resistance test:

[0158] Test method: Simulate drought (soil moisture content 10%) and saline-alkali (soil pH 8.5) environments, plant rapeseed (phosphorus-loving crop), apply the product of Example 1 and traditional phosphate fertilizer, and compare crop survival rate and growth indicators.

[0159] Test results:

[0160] In arid environments, the survival rate of rapeseed in the group using this invention was 85.6%, with a plant height of 42.3 cm and a root length of 28.5 cm; the survival rate in the group using traditional phosphate fertilizer was 62.3%, with a plant height of 31.2 cm and a root length of 19.8 cm.

[0161] In saline-alkali environments, the survival rate of rapeseed in the group using this invention was 82.1%, with a plant height of 39.8 cm and a root length of 26.3 cm; the survival rate in the group using traditional phosphate fertilizer was 58.7%, with a plant height of 28.5 cm and a root length of 17.6 cm.

[0162] Conclusion: The product of this invention, which combines nutrient supply and soil improvement functions, enhances crop resistance to adverse conditions by more than 30%.

[0163] (v) Physical performance testing:

[0164] Test method:

[0165] Compressive strength: Using a particle strength tester, 50 particles were randomly selected to measure the maximum pressure of a single particle when it breaks under compressive stress, and the average value was taken.

[0166] Moisture absorption resistance: After being placed at 25℃ and 85% relative humidity for 72 hours, the moisture absorption weight gain rate was measured.

[0167] Breakage resistance rate: The proportion of particles with a diameter >2mm after vibration was determined by using a simulated transportation vibration test (frequency 50Hz, amplitude 5mm, time 2h).

[0168] The test results are shown in Table 3:

[0169] Table 3

[0170]

[0171] The results show that the product of this invention has high compressive strength, low hygroscopicity, and strong anti-breakage ability, making it easy to store, transport, and apply mechanically.

[0172] (vi) Environmental safety testing:

[0173] Test methods: Refer to "Limits of Harmful Elements in Fertilizers" (GB / T23349-2020) to determine the content of lead, cadmium, mercury, arsenic and chromium in the product; use soil leaching test to determine the content of heavy metals in soil leachate within 30 days after application.

[0174] Test results:

[0175] The harmful element content of the product is as follows: lead < 5 mg / kg, cadmium < 0.1 mg / kg, mercury < 0.05 mg / kg, arsenic < 2 mg / kg, chromium < 10 mg / kg, all of which are far below the national standard limits (lead ≤ 50 mg / kg, cadmium ≤ 10 mg / kg, mercury ≤ 5 mg / kg, arsenic ≤ 10 mg / kg, chromium ≤ 50 mg / kg).

[0176] Soil leachate: No heavy metals were detected, there is no risk of secondary pollution, and it meets the requirements for agricultural environmental safety.

Claims

1. A method for preparing slow-release phosphate fertilizer soil using graphite tailings sand and coal gangue, characterized in that... The method is specifically implemented according to the following steps: I. Pretreatment of graphite tailings: The graphite tailings sand is crushed to a particle size of ≤2mm, and then subjected to gradient magnetic separation. The magnetic field strength in the first stage is 800~1000Gs, and the magnetic field strength in the second stage is 1500~1800Gs to remove magnetic impurities. Then, dilute sulfuric acid solution is added according to a certain liquid-solid ratio, heated and stirred, filtered, washed with water until neutral, and dried to obtain pretreated graphite tailings sand. II. Coal gangue pretreatment: The coal gangue was crushed to a particle size of ≤3mm, then roasted at 400~500℃ to remove organic matter; then activated under microwave power of 600~800W, cooled, and sodium carbonate solution was added at a certain liquid-solid ratio. The mixture was stirred at room temperature, filtered, and dried to obtain pretreated coal gangue. III. Preparation of composite activators: Phosphate rock powder, potassium sulfate, and humic acid are mixed to obtain a mixture; water accounting for 10% to 15% of the total mass of the mixture is added to the mixture and stirred until it becomes a paste. Then, it is aged at 30 to 40°C to obtain a composite activator. IV. Mixed Molding: Pretreated graphite tailings sand, pretreated coal gangue, and composite activator are mixed and fed into a twin-screw extruder. The mixture is extruded and granulated at a melting temperature of 120~150℃ and a rotation speed of 80~100r / min. The particle size is controlled and then dried to obtain slow-release phosphate fertilizer soil.

2. The method for preparing slow-release phosphate fertilizer soil using graphite tailings sand and coal gangue according to claim 1, characterized in that... The mass fraction of the dilute sulfuric acid solution mentioned in step one is 5-8%; the liquid-to-solid ratio mentioned in step one is (3-5):

1.

3. The method for preparing slow-release phosphate fertilizer soil using graphite tailings sand and coal gangue according to claim 1, characterized in that... The heating and stirring temperature in step one is 50~60℃, and the heating and stirring time is 2~3h; the gradient magnetic separation in step one is a counter-current magnetic separator, and the magnetic separation time for each stage is 15~20min.

4. The method for preparing slow-release phosphate fertilizer soil using graphite tailings sand and coal gangue according to claim 1, characterized in that... In step two, the material is calcined at 400-500℃ for 1.5-2 hours; the activation treatment in step two is carried out using a continuous microwave reactor, and the material residence time is controlled by the conveyor belt speed, with an activation treatment time of 15-20 minutes; the mass fraction of the sodium carbonate solution in step two is 3-5%.

5. A method for preparing slow-release phosphate fertilizer soil using graphite tailings sand and coal gangue according to claim 1, characterized in that... The liquid-to-solid ratio in step two is (2~3):1; the stirring time at room temperature in step two is 1~1.5h; the calcination in step two is carried out in a rotary kiln with a heating rate of 5~8℃ / min.

6. The method for preparing slow-release phosphate fertilizer soil using graphite tailings sand and coal gangue according to claim 1, characterized in that... The particle size of the phosphate rock powder mentioned in step three is ≤100 mesh; the mass ratio of phosphate rock powder, potassium sulfate, and humic acid mentioned in step three is 5:2:3; the aging time at 30~40℃ in step three is 8~10h; the P2O5 content in the phosphate rock powder mentioned in step three is ≥30%; the humic acid mentioned in step three is weathered coal humic acid with an organic matter content ≥70%.

7. The method for preparing slow-release phosphate fertilizer soil using graphite tailings sand and coal gangue according to claim 1, characterized in that... In step four, the mass ratio of pretreated graphite tailings sand, pretreated coal gangue, and composite activator is 4:3:3; and the particle size is controlled to be 3-5 mm in step four.

8. A method for preparing slow-release phosphate fertilizer soil using graphite tailings sand and coal gangue according to claim 1, characterized in that... The drying temperature in step four is 80~100℃, and the drying time is 2~3h; the moisture content of the slow-release phosphate fertilizer soil in step four is controlled at 8~12%, and the compressive strength is ≥15N / particle.

9. A slow-release phosphate fertilizer soil, characterized in that... It is prepared according to the method described in any one of claims 1 to 8.

10. The application of a slow-release phosphate fertilizer soil prepared by the method according to any one of claims 1 to 8, characterized in that... Application of a slow-release phosphate fertilizer soil in the cultivation of phosphorus-loving crops; the phosphorus-loving crops include rapeseed, cotton, and tomato; the application rate is 200-300 kg per acre, and it needs to be used in conjunction with 10-15% organic fertilizer.

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