Method for preparing landscaping planting soil from phosphorus chemical solid waste

Abstract

The invention discloses a method for preparing landscaping planting soil from phosphorus chemical solid waste, and belongs to the technical field of resource recycling. The method comprises the following steps: (1) drying, crushing and harmlessly treating phosphate tailings, phosphogypsum and flotation residues; (2) decomposing the organic manure; (3) mixing and aging the raw materials; and (4) granulating. Heavy metal pollution is reduced through innocent treatment, the soil structure is improved by combining organic matter, microorganisms and mineral substances, the nutrient release efficiency and the water-retaining property are remarkably improved, the obtained soil meets the landscaping requirement, and dual improvement of solid waste recycling and ecological benefits is achieved.

Description

Technical Field

[0001] The invention relates to a method for preparing planting soil for landscaping projects by using phosphorus chemical solid waste, belonging to the technical field of resource recycling. Background Art

[0002] The production of phosphate fertilizers by phosphate chemical companies generates a large amount of solid waste. The efficient utilization and proper disposal of this solid waste are crucial for achieving green development. Phosphate tailings, derived from the beneficiation of phosphate rock, are primarily composed of dolomite and calcite. Phosphate tailings are low- to medium-grade phosphate rock with low P2O5 content and high levels of impurities such as calcium, magnesium, iron, and aluminum. Currently, the utilization of phosphate tailings is primarily focused on mine filling, construction material production, fertilizer processing, and resource recycling, but the overall utilization rate is only approximately 7%.

[0003] Phosphogypsum is a solid waste residue produced when phosphate rock is treated with sulfuric acid during phosphoric acid production. It is primarily composed of calcium sulfate, and contains impurities such as ammonium nitrogen, phosphates, and heavy metals, making it highly acidic. Approximately 4.5 to 5 tons of phosphogypsum are produced during the production of every ton of phosphoric acid, with an annual output reaching 80 million tons. Due to its low added value, high utilization costs, and technological limitations, phosphogypsum has a low overall utilization rate. Current utilization primarily involves building materials production, cement retarders, soil conditioners, and acid-co-production of cement. Although the utilization rate has reached 51%, significant stockpiles remain. The long-term storage of solid wastes such as phosphate tailings and phosphogypsum, which remain untreated, occupies significant agricultural and forestry land, causing a series of environmental pollution, ecological damage, and safety issues, becoming a production bottleneck for phosphate fertilizer companies.

[0004] In addition, phosphate tailings and phosphogypsum contain nutrients such as phosphorus, sulfur, calcium, and magnesium, making them suitable for soil conversion. However, their organic matter content is low, requiring the addition of organic-rich substances. Phosphogypsum flotation residue is waste generated during the flotation process for purifying phosphogypsum. Hydrocarbon oil collectors and alcohol, phenol, and sulfonate foaming agents are added to the phosphogypsum, causing organic matter on the surface of the phosphogypsum to adhere to the bubbles and float to the liquid surface. The organic matter is then scraped off by the flotation machine scrapers and dehydrated by a plate and frame filter press. The resulting residue is the phosphogypsum flotation residue. Phosphogypsum flotation residue is a solid waste rich in organic matter and CaCO3, but also contains high concentrations of heavy metal pollutants.

[0005] Because soil resources are limited and landscaping requires a large amount of plant growth substrate, soilification of solid waste is a promising resource utilization method. However, phosphorus chemical solid waste contains excessive amounts of heavy metals, has a single, difficult-to-release composition, and has poor air permeability and drainage, resulting in a lack of nutrients and soil structure that cannot effectively support plant growth, making soilification extremely difficult to implement. Currently, there is no effective method for soilification of phosphorus chemical solid waste. Summary of the Invention

[0006] The purpose of the present invention is to address the defects of the above-mentioned prior art and provide a method for converting phosphorus chemical solid waste into soil and applying it to landscaping planting. The implementation of the present invention will effectively promote the resource recycling of waste and alleviate a series of environmental problems caused by waste discharge.

[0007] To achieve the above object, the present invention uses the following technical solutions: A method for preparing landscaping planting soil using phosphorus chemical solid waste comprises the following steps: (1) Solid waste pretreatment: drying the phosphate tailings, phosphogypsum and phosphogypsum flotation residue to a moisture content of ≤5% and crushing them to a particle size of ≤0.2mm; (2) Harmless treatment of solid waste: Use chelating agents to extract heavy metals from pre-treated solid waste, adjust the pH of the extract after filtration and precipitate heavy metals, and discharge the wastewater after meeting the standards; (3) Composting of organic manure: Mix earthworm manure with conditioner, adjust the carbon-nitrogen ratio to 30-40:1, add probiotic fermentation agent for composting, control the temperature of the pile at 50-65℃, and turn the pile regularly until it is fully decomposed; (4) Mixing and stirring: Mix the harmlessly treated solid waste, decomposed earthworm manure, zeolite, potassium feldspar, soybean meal, water-retaining agent, microbial agent and trace element additives in proportion; (5) Aging treatment: Pile the mixed material in a ventilated environment for 15-30 days and turn the pile regularly; (6) Granulation: The aged material is passed through a disc granulator to prepare particles with a particle size of 5-10 mm, thereby obtaining landscaping planting soil.

[0008] Preferably, the mass ratio of the phosphorus chemical solid waste in step (1) is: 20-30 parts of phosphate tailings, 5-15 parts of phosphogypsum, and 5-6 parts of phosphogypsum flotation residue.

[0009] Preferably, the chelating agent in step (2) is a 150 mM Na2EDTA solution, and the extraction time is 24 hours; the pH of the extract is adjusted to 10 using NaOH, and a 20 mmol / L Na2S solution is added to precipitate heavy metals.

[0010] Preferably, the mass ratio of the raw materials in step (4) is: 30-50 parts of solid waste after harmless treatment, 30-45 parts of decomposed earthworm castings, 3-6 parts of zeolite, 5-10 parts of potassium feldspar, 5-8 parts of soybean meal, 0.5-1 part of microbial agent, 0.2-0.5 part of water retaining agent, and 1-3 parts of trace element additives.

[0011] Preferably, the microbial agent comprises Pseudomonas and Bacillus jelly-like, and the mass ratio of the two is 1:1.

[0012] Preferably, the water-retaining agent is sodium polyacrylate or polyacrylamide.

[0013] Preferably, the conditioning agent in step (3) is straw powder or sawdust.

[0014] In order to overcome the technical difficulties such as excessive heavy metals in phosphorus chemical solid waste, single nutrients that are difficult to release, and poor soil forming properties, the present invention uses a combination of various technical means: (1) removing heavy metals through harmless treatment to reduce environmental pollution; (2) supplementing organic matter and nitrogen, potassium and trace elements to provide nutrients for plant growth and improve plant resistance, while introducing microorganisms to promote the release and absorption of minerals; (3) earthworm manure, soybean meal, zeolite, water-retaining agents, etc. can improve soil structure and enhance soil forming properties.

[0015] The coordinated and consistent nature of the raw materials in this invention, along with their rigorous compatibility, creates a mild overall soil environment, overcomes the inhibitory effects of high salinity and heavy metals on microbial flora, and effectively maintains microbial activity. This formulation can provide sufficient nutrients and a robust soil environment for landscaping, embodying the integration of solid waste resource utilization with ecological agriculture, reducing the use of agricultural fertilizers and achieving significant economic benefits. Furthermore, this invention rigorously manages environmental risks, optimizes nutrient balance and microbial activity, and, after experimental verification, is expected to become a sustainable landscaping soil. DETAILED DESCRIPTION

[0016] The present invention is further described in detail below with reference to specific embodiments.

[0017] Example 1 1. Raw materials 42Kg of phosphorus chemical solid waste, 42Kg of earthworm castings, 5Kg of zeolite (5-20 mesh), 8Kg of potassium feldspar (5-20 mesh), 6Kg of soybean meal, 0.7Kg of microbial agent, 0.3Kg of water retaining agent, and 2Kg of trace element additives.

[0018] 2. Ingredients Phosphorus chemical solid waste: Consists of 30 kg of phosphate tailings, 6 kg of phosphogypsum, and 6 kg of phosphogypsum flotation residue. These wastes contain elements such as phosphorus, calcium, and sulfur, as well as a small amount of organic matter. They also contain heavy metals such as cadmium and lead, which can cause environmental pollution if not handled properly. Furthermore, the solid waste has poor air permeability and drainage, requiring crushing and the introduction of other raw materials for improvement.

[0019] Worm castings: organic fertilizer, rich in humus and microorganisms, it not only provides slow-release nutrients for plant growth, but also improves soil structure and promotes microbial growth.

[0020] Zeolite: Zeolite has adsorption properties, which can improve the soil's ability to retain water and fertilizer, adsorb heavy metals, purify the soil, and is often used in soil improvement.

[0021] Potassium feldspar: Potassium feldspar is a potassium-containing aluminum silicate mineral. After decomposition, it releases potassium to provide nutrients for plant growth, but its decomposition rate is slow and requires the assistance of microorganisms to decompose.

[0022] Soybean meal: Supplements organic nitrogen sources, increases soil permeability and water retention, and promotes plant root growth.

[0023] Water-retaining agent: Sodium polyacrylate, a highly absorbent resin, can absorb a large amount of water and release it slowly, thereby enhancing the soil's water retention capacity.

[0024] Microbial agent: composed of Pseudomonas and Bacillus gelatinus, with a ratio of 1:1, which helps release minerals in the soil and fix nitrogen into a form that can be used by plants. The two bacteria work synergistically to promote nutrient circulation.

[0025] Trace element additives: Contains trace elements such as calcium, magnesium, boron, zinc, iron, molybdenum, and manganese, used to alleviate soil alkalinity and improve plant resistance. This product is a commercially available product purchased from Shandong Foyte Agricultural Technology Co., Ltd.

[0026] 3. Preparation method 1) Solid waste pretreatment: The phosphate tailings, phosphogypsum and phosphogypsum flotation residue were dried at room temperature for 15 days to a moisture content of ≤5%, and then crushed with a jaw crusher to a particle size of ≤0.2mm.

[0027] 2) Harmless treatment of solid waste: Use Na2EDTA to extract heavy metals from solid waste, with a chelating agent concentration of 150mM and an extraction time of 24h. After extraction, filter and set aside the solid waste. The extract is first adjusted to pH 10 with 5mol / L NaOH solution, and then the heavy metals are precipitated with 20mmol / L Na2S solution, so that the wastewater meets the standards before discharge.

[0028] 3) Composting of organic manure: Add appropriate amounts of conditioners, such as straw powder and sawdust, to the vermicompost, adjusting the carbon-nitrogen ratio to 30-40:1 to improve aeration. Then, add a commercially available organic manure probiotic fermentation agent and mix thoroughly. The mixture is then piled into strips 1.2-1.5 meters high and 2-3 meters wide. Turning is generally done every 2-3 days in the early stages, and this can be gradually increased to every 5-7 days in the later stages. Maintain a moisture content of 50%-60% and a temperature of 50-65°C to fully compost the organic material before use. Composting maturity is indicated by the following: Fermentation is essentially complete when the organic manure darkens in color, becoming dark brown or dark brown; its odor changes from its original foul odor to a mild earthy smell; its texture becomes looser and no longer clumping; and its temperature remains stable around ambient temperature, with no significant increase in temperature.

[0029] 4) Mixing and stirring: Add the harmless solid waste, decomposed organic manure, zeolite, potassium feldspar, soybean meal, water-retaining agent, microbial agent and trace element additives into the blender in proportion and stir thoroughly for 15-30 minutes to mix all the components evenly.

[0030] 5) Aging: The mixed materials are piled in a well-ventilated area for aging for 15-30 days, turning the pile regularly. During the aging process, the various components in the materials undergo further physical and chemical reactions, making the physical and chemical properties of the soil more stable and the nutrients more readily available for plant absorption and utilization.

[0031] 6) Granulation. The aged material is placed in the disc of a disc granulator and sprayed with water as a binder. The disc rotates and centrifuges to produce spherical particles with a particle size of 5-10 mm, thus obtaining landscaping soil.

[0032] Example 2 30kg of phosphorus chemical solid waste, 45kg of earthworm castings, 6kg of zeolite (5-20 mesh), 5kg of potassium feldspar (5-20 mesh), 8kg of soybean meal, 0.5kg of microbial agent, 0.5kg of water retaining agent, and 3kg of trace element additives.

[0033] The phosphorus chemical solid waste consists of 20 kg of phosphorus tailings, 5 kg of phosphogypsum, and 5 kg of phosphogypsum flotation residue; The water-retaining agent is polyacrylamide; The microbial agent is composed of Pseudomonas and Bacillus jelly, with a ratio of 2:1; Preparation method: Same as Example 1.

[0034] Example 3 50Kg of phosphorus chemical solid waste, 30Kg of earthworm castings, 3Kg of zeolite (5-20 mesh), 10Kg of potassium feldspar (5-20 mesh), 5Kg of soybean meal, 1Kg of microbial agent, 0.2Kg of water retaining agent, and 1Kg of trace element additives.

[0035] The phosphorus chemical solid waste consists of 30 kg of phosphorus tailings, 15 kg of phosphogypsum, and 5 kg of phosphogypsum flotation residue; The water-retaining agent is sodium polyacrylate; The microbial agent is jelly-like Bacillus; Preparation method: Same as Example 1.

[0036] Test example 1. Potted Plant Experiment The prepared landscaping soil was placed in 1-gallon, 15.5-cm-diameter pots, with 1.8 kg of soil added to each pot. Pansy seedlings were then transplanted into the pots. Ryegrass seeds, soaked in darkness at 25°C for 48 hours, were sprinkled into the landscaping soil. Both pansy seedlings and ryegrass seeds were harvested after one month of greenhouse cultivation. Their growth was observed and recorded, and post-harvest measurements of plant root length, biomass, and other indicators were measured. A soil control group was also established, with five replicates per treatment. The results are shown in Tables 1 and 2.

[0037] Table 1: Comparison of growth indicators of pansy planted in different treatments

[0038] Table 2: Comparison of ryegrass growth indicators in different treatments

[0039] Results: The root-to-shoot ratio (R / S) is the ratio of a plant's root biomass to its aboveground biomass and is an important indicator of a plant's resource allocation and growth strategy. Differences in plant R / S reflect adaptive changes in resource allocation strategies. A higher R / S ratio indicates that the plant preferentially allocates assimilated products to root development. This morphological trait helps enhance water and nutrient uptake efficiency and is a typical adaptive mechanism for coping with poor soils or drought stress. Conversely, a lower R / S ratio indicates that the plant tends to promote aboveground growth, adapting to nutrient-rich environments by increasing photosynthetic area and reproductive tissue development. Pansy and ryegrass growth results showed that the planting soil prepared in this invention promoted better root development, longer root length, and better aboveground growth in both pansy and ryegrass. Overall, this was reflected in a lower R / S ratio and higher aboveground biomass, indicating that the soil was nutrient-rich and capable of supporting plant growth.

[0040] 2. Phosphorus and Potassium Release Experiment Experimental Methods: Prepared soil was dispensed into sealed polyethylene pots (500 g each) and incubated at 25 ± 2°C for 30 days. Deionized water was regularly added to maintain the soil moisture content at 60%-70% of field capacity. Three replicate samples were collected from each group at different time points (e.g., day 0, day 7, day 14, day 21, and day 28) to determine the available phosphorus and available potassium content in the soil.

[0041] Available phosphorus was determined using the molybdenum antimony colorimetric method described in LY / T 1232. The specific experimental steps are as follows: Weigh 2.5 g of the prepared greening soil into a 200 ml plastic bottle, add 50 ml of sodium bicarbonate extractant, and then shake at 180 rpm for 30 minutes before filtering to obtain the extract. Pipette 10.00 ml of the sample solution into a 25 ml colorimetric tube, slowly add 5.00 ml of molybdenum antimony colorant, and shake gently; then add distilled water to the volume. After standing at room temperature above 20°C for 30 minutes, perform the colorimetric determination using a 1 cm optical path cuvette at a wavelength of 880 nm, adjusting the zero point to the standard solution.

[0042] Available potassium was determined using the flame photometric method described in LY / T1234. The specific steps are as follows: 5.00 g of air-dried sample, passed through a 2 mm sieve, was weighed into a 200 mL plastic bottle. 50 mL of 1 mol / L ammonium acetate solution (soil-to-liquid ratio of 1:10) was added. The bottle was tightly capped and shaken. The sample was shaken at 150-180 rpm for 30 minutes at 15-25°C. The sample was filtered and the filtrate was measured directly using a flame photometer or, after appropriate dilution, using an atomic absorption spectrophotometer. A blank test was also performed.

[0043] The test results are shown in Tables 3 and 4.

[0044] Table 3: Phosphorus release dynamics in greening planting soil (unit: mg / kg)

[0045] Table 4: Potassium release dynamics in greening planting soil (unit: mg / kg)

[0046] Phosphorus release analysis: Soil control: Low initial value, slow growth. Example 1: High initial value (35.2 mg / kg), rapid release (+66%) within 7 days, slowing after 14 days, reaching 92.1 mg / kg in 28 days. Example 2: High proportion of vermicompost resulted in rapid initial release, but low proportion of solid waste, resulting in slower growth later, reaching only 73.8 mg / kg in 28 days. Example 3: High proportion of solid waste, but low proportion of vermicompost and microbial inoculants, slowed release (65.4 mg / kg).

[0047] Potassium Release Analysis: Example 1: Potassium feldspar and microbial inoculants exhibited significant synergy, achieving a 28-day fast-acting potassium release of 360.7 mg / kg, with a flat and stable release curve. Example 2: An imbalance in the microbial inoculant ratio resulted in reduced potassium release efficiency (305.2 mg / kg). Example 3: Containing only Bacillus jelly, the mineral decomposition capacity was insufficient, resulting in a low release rate (290.1 mg / kg).

[0048] In summary, the garden soil prepared by the present invention provides a continuous source of organic matter and minerals. The microbial agent promotes mineral decomposition and steadily releases fixed phosphorus and potassium. Zeolite and water-retaining agents improve the soil microenvironment and slow nutrient loss. The total amount and rate of mineral release in Example 1 were superior to those in the other treatments.

[0049] 3. Heavy metal detection Detection method: Accurately weigh 0.5g of uniform solid waste powder into a polytetrafluoroethylene crucible, then add 5mL of concentrated nitric acid, 10mL of hydrofluoric acid, and 4mL of perchloric acid. Cover and place on a hot plate in a fume hood. Heat at 220°C until the solids are completely dissolved and the solution is transparent or white. If digestion is incomplete, add 3mL of concentrated nitric acid to digest. After digestion is complete, open the lid and continue heating at 150°C to remove the acid until the white smoke disappears. Remove the crucible from the hot plate, cool slightly, add 3mL of concentrated nitric acid to dissolve the soluble salts, and then transfer the entire amount to a 50mL volumetric flask to the final volume. Use a plasma emission spectrometer to determine the heavy metal concentration in the solution and calculate the heavy metal content in the sample. The test results are shown in Table 5.

[0050] Table 5 Heavy metal content of each example (unit: mg / kg)

[0051] The heavy metal content of the soil prepared in each example is lower than the heavy metal content standard requirement of CJ / T340-2016 for greening planting soil during urban construction, indicating that the prepared greening planting soil does not cause heavy metal pollution to the environment and plants.

[0052] 4. Determination of porosity and water retention Test Method: Porosity was calculated by measuring soil bulk density and specific gravity. Bulk density was determined using the ring knife method; specific gravity was determined using the pycnometer method. Total porosity was then calculated using the formula: Total porosity (%) = (1 - specific gravity / bulk density) × 100. Water retention was determined using an in-situ method: After saturation with water, the soil was covered with a film to prevent evaporation. After 48 hours, samples were taken and measured using a pressure membrane instrument under a negative pressure of 0.33 bar (approximately 1 / 3 atm). The test results are shown in Table 6.

[0053] Table 6 Porosity and water retention rate of each embodiment (%)

[0054] The total porosity and water retention rate of the garden planting soil prepared by the present invention are higher than those of the soil control group, which may be related to the use of additives such as organic fertilizer, zeolite, soybean meal, and a suitable granulation process in the present invention.

[0055] The preferred embodiments of the present invention have been specifically described above, but the present invention is not limited to the described embodiments. Those skilled in the art may make various equivalent modifications or substitutions without departing from the spirit of the present invention. These equivalent modifications or substitutions are all included in the scope defined by the claims of this application.

Claims

1. A method for preparing landscaping planting soil using phosphorus chemical solid waste, characterized in that: The following steps are involved: (1) Solid waste pretreatment: drying the phosphate tailings, phosphogypsum and phosphogypsum flotation residue to a moisture content of ≤5% and crushing them to a particle size of ≤0.2mm; (2) Harmless treatment of solid waste: Use chelating agents to extract heavy metals from pre-treated solid waste, adjust the pH of the extract after filtration and precipitate heavy metals, and discharge the wastewater after meeting the standards; (3) Composting of organic manure: Mix earthworm manure with conditioner, adjust the carbon-nitrogen ratio to 30-40:1, add probiotic fermentation agent for composting, control the temperature of the pile at 50-65℃, and turn the pile regularly until it is fully decomposed; (4) Mixing and stirring: Mix the harmlessly treated solid waste, decomposed earthworm manure, zeolite, potassium feldspar, soybean meal, water-retaining agent, microbial agent and trace element additives in proportion; (5) Aging treatment: Pile the mixed material in a ventilated environment for 15-30 days and turn the pile regularly; (6) Granulation: The aged material is passed through a disc granulator to prepare particles with a particle size of 5-10 mm, thereby obtaining landscaping planting soil.

2. The method according to claim 1, characterized in that The mass ratio of the phosphorus chemical solid waste in step (1) is: 20-30 parts of phosphorus tailings, 5-15 parts of phosphogypsum, and 5-6 parts of phosphogypsum flotation residue.

3. The method according to claim 1, characterized in that The chelating agent in step (2) is a 150 mM Na2EDTA solution, and the extraction time is 24 hours; the pH of the extract is adjusted to 10 using NaOH, and a 20 mmol / L Na2S solution is added to precipitate heavy metals.

4. The method according to claim 1, wherein The mass ratio of the raw materials in step (4) is: 30-50 parts of solid waste after harmless treatment, 30-45 parts of decomposed earthworm castings, 3-6 parts of zeolite, 5-10 parts of potassium feldspar, 5-8 parts of soybean meal, 0.5-1 part of microbial agent, 0.2-0.5 part of water retaining agent, and 1-3 parts of trace element additives.

5. The method according to claim 1, wherein The microbial agent comprises Pseudomonas and Bacillus jelly, and the mass ratio of the two is 1:

1.

6. The method according to claim 1, characterized in that The water-retaining agent is sodium polyacrylate or polyacrylamide.

7. The method according to claim 1, characterized in that The conditioning agent in step (3) is straw powder or sawdust.

Images