Method for preparing soil conditioner from sulfur-containing tailings

Abstract

The invention discloses a method for preparing a soil conditioner from sulfur-containing tailings, a multifunctional soil conditioner is prepared through aging pretreatment, high-temperature activation, sulfur resource recovery and nutrient synergistic blending, and the method is suitable for ecological restoration of mining areas and degraded soil improvement. SO2 is efficiently oxidized and absorbed and converted into sulfuric acid through a two-stage absorption system and a spraying liquid with a specific formula, the sulfuric acid is subsequently used for tailings neutralization, closed-loop circulation of sulfur elements from tailings waste to product components is achieved, and the utilization rate of sulfur resources is greatly increased; meanwhile, unstable sulfides can be effectively decomposed in the high-temperature calcination process, so that part of heavy metals are converted into more stable forms, and the environmental risk is eliminated; venturi washing waste liquid and absorption tower circulating liquid are recycled to respective systems, so that the wastewater generation amount and the fresh water consumption are remarkably reduced.

Description

Technical Field

[0001] This invention relates to the field of soil improvement technology, and specifically to a method for preparing soil conditioners using sulfur-containing tailings. Background Technology

[0002] With the large-scale development and utilization of mineral resources, the amount of sulfur-containing tailings generated during the mining, beneficiation, and smelting processes of metal mines has been increasing year by year. These tailings are typically rich in sulfides (such as pyrite and pyrrhotite). If stored for a long period without effective disposal measures, they will undergo oxidation reactions upon exposure to air, water, and microorganisms, producing acidic mine wastewater. This wastewater severely pollutes surrounding soil, surface water, and groundwater, disrupts the ecological balance, and even threatens human health through the food chain. Statistics show that my country's metal mines alone generate hundreds of millions of tons of sulfur-containing tailings annually. The large accumulation of tailings not only occupies valuable land resources but also poses a significant threat to regional environmental pollution. Its harmless disposal and resource utilization have become critical issues urgently needing to be addressed in the environmental protection field.

[0003] Meanwhile, soil degradation is becoming increasingly severe globally, and my country's arable land faces multiple challenges, including salinization, acidification, compaction, and declining fertility. According to relevant data, my country's total saline-alkali land area exceeds 500 million mu (approximately 33.3 million hectares), and acidic soil accounts for 22.7% of arable land. Soil degradation directly leads to reduced crop yields and quality, severely restricting sustainable agricultural development. Soil conditioners, as an important means of improving soil physicochemical properties and enhancing soil fertility, are experiencing continuous market demand growth. Currently, commonly used soil conditioners are mostly made from limestone, gypsum, organic fertilizers, and industrial waste (such as steel slag and fly ash), but these suffer from high raw material costs, limited functionality, and insufficient adaptability to specific degraded soils. For example, conditioners for saline-alkali land often require the supplementation of cations such as calcium and magnesium to replace sodium ions, while acidic soil conditioning requires alkaline substances to neutralize acidity. Developing soil conditioners with multiple improvement functions and widely available raw materials would significantly improve soil improvement efficiency and reduce application costs.

[0004] While there have been attempts to use industrial tailings for soil improvement in existing technologies, research on the resource utilization of sulfur-containing tailings still has significant limitations. On the one hand, due to their inherent acidity potential and heavy metal risks, direct application of sulfur-containing tailings can easily exacerbate secondary soil pollution, requiring complex pretreatment (such as neutralization and stabilization), resulting in excessively high process costs. On the other hand, existing processes mostly focus on the harmless treatment of tailings, failing to fully explore their intrinsic value—the sulfur element in sulfur-containing tailings can be converted into sulfate to supplement the soil with sulfur nutrients (sulfur is an essential medium element for crop growth). At the same time, the calcium, magnesium, and other mineral components contained in the tailings can play a role in regulating soil pH and improving soil structure after appropriate treatment.

[0005] Therefore, how to achieve the synergy of pollution risk control and efficient resource utilization of sulfur-containing tailings through reasonable process design, and prepare soil conditioners with functions such as pH adjustment, nutrient supplementation, and heavy metal passivation, has become an innovative direction for solving the problems of sulfur-containing tailings pollution and soil degradation, and has important environmental benefits and economic value. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention aims to provide a method for preparing soil conditioners using sulfur-containing tailings. Through aging pretreatment, high-temperature activation, sulfur resource recovery, and nutrient synergistic blending, a multifunctional soil conditioner is prepared, suitable for ecological restoration of mining areas and improvement of degraded soils.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A method for preparing a soil conditioner using sulfur-containing tailings includes the following steps:

[0009] (1) Screening and fine grinding:

[0010] The sulfur-containing tailings are screened, and the undersize material enters the fine grinding system for grinding, with the output particle size controlled to be ≤0.15mm. The oversize material is returned for crushing and then screened again.

[0011] (2) Aging treatment:

[0012] After the sulfur-containing tailings that have been finely ground by the fine grinding system are thoroughly mixed with calcium oxide, sodium hydroxide, dolomite powder and potassium feldspar powder, water is added to the resulting tailings mixture, the mixture is stirred evenly and then left to stand for aging, then air-dried, and then placed in an oven to dry, and finely ground to a particle size of less than 0.15 mm.

[0013] (3) High-temperature activation and flue gas absorption:

[0014] The tailings mixture obtained from the aging process in step (2) is fed into a rotary kiln for calcination. The generated flue gas enters a plate heat exchanger through a Venturi scrubber to wash the flue gas dust and reduce the flue gas temperature. Then, the flue gas is sequentially fed into a sieve plate absorption tower and a packed tower. In the sieve plate absorption tower and the packed tower, sulfur dioxide is oxidized and absorbed by spraying a spraying liquid onto the flue gas.

[0015] The absorbent obtained after the spray liquid interacts with the flue gas is fed into the inclined tube sedimentation tank for settling. The supernatant obtained from the settling is returned to the sieve plate absorption tower and the packed tower as absorbent for recycling. The sludge generated from the settling is dewatered by filter press. The solid obtained from the filter press is tested for heavy metal content. Under the condition that it does not exceed the required limit, the solid obtained from the filter press is mixed with the calcined tailings mixture to obtain the tailings mixture. The filtrate obtained from the filter press is mixed with the discharged supernatant to form an acid solution.

[0016] (4) Activation and neutralization of tailings:

[0017] The acid solution produced in step (3) is mixed with potassium dihydrogen phosphate and reacted. Then a dispersant is added and stirred. After that, the tailings mixture obtained in step (3) is added and stirred to neutralize, so as to obtain the neutralized tailings mixture.

[0018] (5) Formulation and Granulation:

[0019] The neutralized tailings mixture obtained in step (4) is tested and compared for effective silicon, calcium, potassium and magnesium elements. One or more of diatomaceous earth, potassium chloride and superphosphate are added as needed and mixed evenly. Then, a composite disintegrant is added to the mixture, granulated and shaped, and then dried and sieved to obtain the soil conditioner product.

[0020] Further, in step (2), the solid-liquid mass ratio of the tailings mixture to water is 1:0.8-1:1.5; after adding water to the tailings mixture, it is stirred at 20-60℃ for 1-2 hours and then left to stand for aging for 24-48 hours, and then naturally dried until the moisture content is below 10%.

[0021] Further, in step (2), the amount of calcium oxide added is 10%-40% of the mass of the finely ground sulfur-containing tailings, the amount of sodium hydroxide added is 5%-20% of the mass of the finely ground sulfur-containing tailings, the amount of dolomite powder added is 5%-20% of the mass of the finely ground sulfur-containing tailings, and the amount of potassium feldspar powder added is 5%-20% of the mass of the finely ground sulfur-containing tailings; the fineness of the dolomite powder is ≤0.15mm, and the fineness of the potassium feldspar powder is ≤0.15mm.

[0022] Furthermore, in step (3), the fresh spray liquid contains 20-25% H2O2 and 0.01%-0.05% phosphoric acid by mass percentage.

[0023] Further, in step (3), the calcination temperature is 800-1100℃, the calcination time is 1-2h, and the excess air coefficient is controlled at 1.2-1.5; the inlet flue gas velocity of the Venturi scrubber is controlled at 20-30m / s, the waste liquid containing coarse dust generated by the scrubbing is introduced into the inclined tube sedimentation tank, the supernatant in the inclined tube sedimentation tank is returned to the Venturi scrubber for water replenishment, and the bottom sludge in the inclined tube sedimentation tank is mixed with the sludge generated by the inclined tube sedimentation tank and then filtered together; the inlet flue gas temperature of the sieve plate absorption tower is controlled at 60-80℃, and the liquid-to-gas ratio in the sieve plate absorption tower is 3-5L / Nm 3 The liquid-to-gas ratio in the packed tower is 1-2 L / Nm³. 3 The pH of the spray solution is maintained at 2.5-3.5; the amount of solids obtained by pressure filtration is 5% of the dry weight of the calcined tailings mixture.

[0024] Furthermore, in step (3), when the sulfuric acid concentration in the supernatant reaches 30%-35% in the inclined tube sedimentation tank, 10%-30% of the volume of supernatant is discharged, and the loss of supernatant is replenished with fresh spray liquid.

[0025] Further, in step (4), the molar ratio of sulfuric acid to potassium dihydrogen phosphate in the acid solution is 0.8-1.2:1, and the reaction temperature of the acid solution and potassium dihydrogen phosphate is 60℃-80℃; the amount of dispersant added is 0.5%-1% of the mass of the tailings mixture, and the dispersant is composed of sodium hexametaphosphate, sodium polyacrylate and lignin sulfonate, and the mass ratio of sodium hexametaphosphate, sodium polyacrylate and lignin sulfonate is (5-8):(1-3):(1-2); the pH value of the neutralized tailings mixture is between 8 and 11.

[0026] Furthermore, in step (5), assuming the test results of the neutralized tailings admixture, the mass percentages of Si, Ca, K2O, and Mg are a, b, c, and d respectively, then:

[0027] Based on the purity requirements of the added diatomaceous earth (SiO2 mass percentage ≥ 85%, Si percentage 46.7%), the mass percentage of diatomaceous earth in the final soil conditioner product is calculated using the following formula:

[0028]

[0029] If a≥9, then the amount of diatomaceous earth added is 0;

[0030] Based on the assumption that the potassium content in the added potassium chloride, converted to K2O, is ≥60% by mass, the mass percentage of potassium chloride in the final soil conditioner product is calculated using the following formula:

[0031]

[0032] If c≥3, then the amount of potassium chloride added is 0;

[0033] Based on the conversion of Ca and Mg in the added superphosphate into CaO and MgO, with CaO mass percentage ≥25% and MgO mass percentage ≥1%, and Ca conversion coefficient 0.714 and Mg conversion coefficient 0.833, the mass percentage of superphosphate in the final soil conditioner product is calculated using the following formula:

[0034]

[0035] If b≥20 and d≥2, then the amount of superphosphate added is 0.

[0036] Further, in step (5), after granulation, the soil conditioner product is dried at 60-80℃ for 30-60 min and then placed in a sulfurized bed for cooling for 10-30 min for sieving to obtain a soil conditioner product with a particle size of 2-4 mm.

[0037] Further, in step (5), the amount of compound disintegrant added is 0.5%-1.5% of the total mass of the mixture; the compound disintegrant includes bentonite, pregelatinized starch, sodium carboxymethyl starch and citric acid residue, and the mass ratio of bentonite, pregelatinized starch, sodium carboxymethyl starch and citric acid residue is (3-5):(1-2):(0.5-1):(1-2). First, the bentonite and citric acid residue are dry mixed for 3-6 minutes, then the pregelatinized starch and sodium carboxymethyl starch are added and mixed for 5-10 minutes, and then mixed with the mixture; granulation is carried out by disc or extrusion granulation, and the proportion of particles with a diameter of 2-4 mm is ≥80%; the moisture content of the dried output is controlled within 8%; the dried output is screened by 2 mm and 4 mm double-layer screens, the fine powder under the screen with a particle size <2 mm is returned to participate in granulation, and the coarse particles on the screen with a diameter >4 mm are crushed and returned to participate in granulation.

[0038] The beneficial effects of this invention are as follows:

[0039] (1) In this invention, SO2 is efficiently oxidized and absorbed and converted into sulfuric acid through a two-stage absorption system and a specific formula spray liquid, which is then used for tailings neutralization, realizing a closed-loop cycle of sulfur from tailings waste to product components, and greatly improving the utilization rate of sulfur resources; at the same time, the high-temperature calcination process can effectively decompose unstable sulfides, converting some heavy metals into more stable forms and eliminating environmental risks; the Venturi washing waste liquid and the absorption tower circulating liquid are both recycled to their respective systems, significantly reducing the amount of wastewater generated and the consumption of fresh water.

[0040] (2) In this invention, finely ground tailings are mixed with calcium oxide, sodium hydroxide, dolomite powder and potassium feldspar powder and aged. Under alkaline and warm conditions, the surface modification of minerals and the pre-release of nutrients such as silicon, potassium and magnesium are promoted, laying the foundation for subsequent high-temperature activation. High-temperature calcination causes the inert silicates and dolomite in the tailings and additives to undergo thermal decomposition and recombination, transforming the insoluble silicon, calcium, potassium and magnesium into an effective form that is more easily absorbed by crops.

[0041] (3) This invention utilizes self-produced acid solution to react with potassium dihydrogen phosphate, and neutralizes high-temperature activated tailings under the action of a specific dispersant, effectively adjusting the pH to the target range and preventing material agglomeration, thus ensuring the uniformity of subsequent granulation; a specially formulated composite disintegrant is used to significantly improve the powder's adhesion, granulation rate and particle strength.

[0042] (4) In accordance with the requirements, the present invention detects and controls the effective silicon, calcium, potassium and magnesium content of the neutralized material to ensure that the core nutrient indicators of the product are stable and meet the standards, and increases the sulfur and phosphorus content to enhance the product's function. In addition, the added components (such as dolomite powder and diatomite) also help to improve the physical structure of the soil (such as air permeability and water retention).

[0043] (5) This invention transforms sulfur-containing tailings, a large amount of industrial solid waste, into a multifunctional soil conditioner with commercial value, realizing "using waste to treat waste and turning waste into treasure". The core raw materials (tailings and self-produced sulfuric acid) in the process are inexpensive, and the amount of auxiliary materials added is precisely controlled by calculation, thus optimizing the formula cost. Attached Figure Description

[0044] Figure 1 This is a flowchart of the method in Embodiment 1 of the present invention. Detailed Implementation

[0045] The present invention will be further described below with reference to the accompanying drawings. It should be noted that this embodiment is based on the present technical solution and provides detailed implementation methods and specific operation processes, but the protection scope of the present invention is not limited to this embodiment.

[0046] Example 1

[0047] Using a sulfur-containing tailings ore as raw material, the multi-element composition and heavy metal analysis results are shown in Tables 1 and 2.

[0048] Table 1. Multi-element analysis results of sulfur-bearing tailings

[0049]

[0050] Table 2. Heavy metal content in sulfur-bearing tailings

[0051]

[0052]

[0053] This embodiment provides a method for preparing a soil conditioner using the aforementioned sulfur-containing tailings, such as... Figure 1 As shown, it includes the following steps:

[0054] (1) Screening and fine grinding

[0055] Sulfur-containing tailings are screened using a double-layer vibrating screen (amplitude 3-5mm, frequency 50Hz). The upper screen has a mesh size of 3mm, and the lower screen has a mesh size of 1mm. The undersize material is tailings particles with a particle size ≤1mm, and the oversize material (>3mm) is conveyed to a jaw crusher for crushing and then returned to the double-layer vibrating screen for screening.

[0056] A horizontal ball mill (lined with wear-resistant ceramic) was selected for fine grinding, with a ball-to-material ratio of 3:1 and Φ15mm alumina balls as the grinding media. The mill speed was controlled at 300 r / min, and frequency conversion speed regulation was used to ensure a discharge particle size of 0.12mm (99% passing through a 100-mesh sieve). The specific surface area of ​​the tailings after fine grinding was ≥320m². 2 / kg.

[0057] (2) Aging treatment

[0058] Using the mass of finely ground sulfur-containing tailings as 100% as a baseline, 20% by mass of calcium oxide (92% CaO purity), 10% by mass of sodium hydroxide (98% NaOH purity), 8% by mass of dolomite powder (38% CaO+MgO purity, fineness ≤0.15mm), and 7% by mass of potassium feldspar powder (9.5% K2O purity, fineness ≤0.15mm) were added to the finely ground sulfur-containing tailings to obtain a tailings mixture. The tailings mixture was then fed into a twin-shaft paddle mixer, and water was added at a solid-liquid mass ratio of 1:1.2. The mixture was stirred at 40℃ and 200r / min for 1.5h, then transferred to an aging tank and allowed to stand for 36h. It was then naturally dried until the moisture content was 10%, and then dried at 80℃ until the moisture content was <5%. Finally, it was finely ground to 0.12mm.

[0059] (3) High-temperature activation and flue gas absorption

[0060] The tailings mixture obtained from the aging process in step (2) was fed into a Φ1.5m×15m rotary kiln. Natural gas heating was used to control the kiln head at 850℃ and the kiln tail at 1050℃, with an excess air coefficient of 1.3. The material residence time was 1.5 hours, and the active silicon content reached 27%. The flue gas generated during calcination was dusted by a Venturi scrubber (inlet flue gas velocity 25m / s), cooled to 70℃ by a plate heat exchanger, and then entered a sieve plate absorption tower (liquid-to-gas ratio 4L / Nm³). 3 ) and packed tower (liquid-to-gas ratio 1.5L / Nm 3In the sieve plate absorber and packed tower, a spray liquid is sprayed onto the flue gas. The fresh spray liquid contains 22% H2O2 and 0.03% phosphoric acid by mass percentage, with the pH value controlled at 3.0 and an SO2 absorption rate of 98.5%. The absorbent obtained after the spray liquid interacts with the flue gas is introduced into an inclined tube sedimentation tank for settling. The supernatant obtained from the settling is returned to the sieve plate absorber and packed tower for recycling. When the sulfuric acid mass concentration in the supernatant reaches 32%, 20% of the supernatant volume is discharged, and fresh spray liquid is added to the inlet of the circulating pump or the circulating liquid tank of the sieve plate absorber and packed tower to make up for the loss of supernatant. After the sludge obtained from sedimentation is filtered, the solid obtained from the filter press (the heavy metal test shall not exceed the limit of GB / T 36207-2018) is mixed with the calcined tailings mixture at 3% of the dry weight of the calcined tailings mixture to obtain a tailings mixture. The filtrate obtained from the filter press is mixed with the discharged supernatant to form an acid solution.

[0061] (4) Tailings activation and neutralization

[0062] The acid solution obtained in step (3) and potassium dihydrogen phosphate were added to a reaction vessel and stirred at 65°C for 1 hour. Then, 0.8% (by weight of the tailings blend) of dispersant (sodium hexametaphosphate:sodium polyacrylate:lignin sulfonate in a mass ratio of 6:2:1) was added and stirred to mix. Subsequently, tailings blend was added again at a solid-liquid mass ratio of 1:0.8, and the mixture was stirred and neutralized in a twin-screw mixer for 30 minutes. The pH of the neutralized tailings blend was 9.2. The molar ratio of sulfuric acid to potassium dihydrogen phosphate in the acid solution was 1:1.

[0063] (5) Compatibility and Granulation

[0064] The neutralized tailings admixture was tested and found to contain 10.8% Si, 25.2% Ca, 4.8% K₂O, and 2.7% Mg by mass percentage. Therefore, there was no need to add diatomaceous earth, potassium chloride, or superphosphate. Instead, a composite disintegrant (bentonite: pregelatinized starch: sodium carboxymethyl starch: citric acid residue mass ratio of 4:1.5:0.8:1.2) was added directly at 1% of the neutralized tailings admixture mass. First, the bentonite and citric acid residue were dry-mixed for 5 minutes. Then, the pregelatinized starch and sodium carboxymethyl starch were added and mixed for 5 minutes. Next, the neutralized tailings admixture was added, and the mixture was wet-mixed with water for 8 minutes. The mixture was then granulated using a disc granulator, dried at 80℃ for 50 minutes, cooled to 18℃ for 20 minutes, and sieved to obtain the finished soil conditioner (2-4 mm).

[0065] Testing showed that the prepared soil conditioner met the Type I standard in GB / T 36207-2018, with a phosphorus (P2O5) content of 4.3%, a sulfur content of 2.9%, a single particle compressive strength of 11N, and heavy metal leaching levels all below the standard limits.

[0066] In this embodiment, the dried material is discharged using a double-layer screen of 2mm and 4mm. Fine powder with a particle size <2mm is returned to the disc granulator to participate in granulation, while coarse particles with a particle size >4mm are crushed and then returned to the disc granulator to participate in granulation.

[0067] Example 2

[0068] This embodiment provides a method for preparing a soil conditioner using sulfur-containing tailings. The sulfur-containing tailings are the same as those in Example 1, as shown in Tables 1 and 2. This embodiment is basically the same as Example 1, with the main difference being:

[0069] In step (1), the particle size of the finely ground material is 0.15 mm.

[0070] In step (2), using the mass of finely ground sulfur-containing tailings as 100%, 10% of the mass of sulfur-containing tailings, 90% calcium oxide (CaO), 5% of the mass of sulfur-containing tailings, 96% sodium hydroxide (NaOH), 5% of the mass of sulfur-containing tailings, 35% dolomite powder (CaO+MgO, fineness ≤0.15mm), and 5% of the mass of sulfur-containing tailings, 8% potassium feldspar powder (K2O, fineness ≤0.15mm) were added to obtain a tailings mixture. The solid-liquid mass ratio of the tailings mixture to water was 1:0.8. The stirring conditions in the twin-shaft paddle mixer were 20℃ and 200r / min for 1 hour, and the aging time was 24 hours.

[0071] In step (3), the calcination conditions are calcination at 800℃ for 1 hour, with an excess air coefficient controlled at 1.2. The inlet flue gas velocity of the Venturi scrubber is 20 m / s, and the liquid-to-gas ratio of the sieve plate absorber is 3 L / Nm³. 3 The liquid-to-gas ratio of the packed tower is 1 L / Nm³. 3 The fresh spray solution contains 20% H2O2 and 0.01% phosphoric acid, with the pH value controlled at 2.5 and an SO2 absorption rate of 96%. When the supernatant obtained from sedimentation in the inclined tube settling tank reaches a sulfuric acid concentration of 30%, 10% of its volume is discharged. The sludge obtained from sedimentation is filtered and then mixed with the calcined tailings mixture at 5% of the dry weight of the calcined tailings mixture.

[0072] In step (4), the molar ratio of sulfuric acid to potassium dihydrogen phosphate in the acid solution is 0.8:1, and the mixing reaction conditions are 60℃ and stirring for 1 hour. The amount of dispersant added is 0.5% of the tailings blend mass, and the mass ratio of sodium hexametaphosphate:sodium polyacrylate:lignin sulfonate in the dispersant is 5:1:1. The stirring and neutralization time in the twin-screw mixer is 15 minutes, and the pH value of the neutralized tailings blend is 8.0.

[0073] In step (5), the neutralized tailings mixture is tested and found to contain Si = 8.5%, Ca = 15.2%, K₂O = 3.0%, and Mg = 1.8% by mass percentage. No further addition of diatomaceous earth and potassium chloride is required, but superphosphate must be added.

[0074] The percentage of superphosphate in the final soil conditioner product is calculated using the following formula:

[0075] Calcium requirement: (20.0% - 15.2%) / (0.714 × 25%) ≈ 26.89%,

[0076] Magnesium supplementation requirement: (2.0% - 1.8%) / (0.833 × 1%) ≈ 24.01%.

[0077] Taking the maximum value, the superphosphate accounts for 26.89% of the final soil conditioner product by mass.

[0078] Add a composite disintegrant (bentonite: pregelatinized starch: sodium carboxymethyl starch: citric acid residue in a mass ratio of 3:1:0.5:1) at 0.5% of the weight of the neutralized tailings mixture. After granulation, dry at 60℃ for 60 min and then cool to 18℃.

[0079] Testing revealed that the silicon, calcium, potassium, and magnesium content in the soil conditioner prepared in this embodiment met the Type I standard in GB / T 36207-2018, the single-particle compressive strength was 9N, and the heavy metal leaching amount was all below the standard limit.

[0080] Example 3

[0081] This embodiment provides a method for preparing a soil conditioner using sulfur-containing tailings, the multi-element composition of which is shown in Table 3.

[0082] Table 3. Multi-element analysis results of high-sulfur tailings

[0083] element TS <![CDATA[SiO2]]> CaO MgO <![CDATA[K2O]]> content(%) 18.52 45.65 3.26 1.23 0.51

[0084] The method in this embodiment is basically the same as that in Embodiment 1, with the main difference being:

[0085] In step (1), the particle size of the finely ground material is 0.15 mm.

[0086] In step (2), based on the mass of finely ground sulfur-containing tailings as 100%, 40% of the mass of sulfur-containing tailings, 90% of calcium oxide (CaO), 20% of the mass of sulfur-containing tailings, 96% of the mass of sodium hydroxide (NaOH), 20% of the mass of sulfur-containing tailings, 35% of dolomite powder (CaO+MgO, fineness ≤0.15mm), and 20% of the mass of sulfur-containing tailings, 8% of the mass of potassium feldspar powder (K2O, fineness ≤0.15mm) were added. The solid-liquid mass ratio of the tailings mixture to water was 1:1.5. The stirring conditions in the twin-shaft paddle mixer were 60℃ and 200r / min for 2 hours, and the aging time was 48 hours.

[0087] In step (3), the calcination conditions are calcination at 1100℃ for 2 hours, with an excess air coefficient controlled at 1.5. The inlet flue gas velocity of the Venturi scrubber is 30 m / s, and the liquid-to-gas ratio of the sieve plate absorber is 5 L / Nm³. 3 The liquid-to-gas ratio of the packed tower is 2 L / Nm³. 3 The fresh spray solution contains 25% H2O2 and 0.05% phosphoric acid by mass percentage, with the pH value controlled at 3.5 and an SO2 absorption rate of 98.7%. When the sulfuric acid concentration in the supernatant obtained from the inclined tube sedimentation tank reaches 35%, 30% of its volume is discharged.

[0088] In step (4), the molar ratio of sulfuric acid to potassium dihydrogen phosphate in the acid solution is 1.2:1, and the mixing reaction conditions are 80℃ and stirring for 1 hour. The amount of dispersant added is 1% of the mass of the tailings blend, and the mass ratio of sodium hexametaphosphate:sodium polyacrylate:lignin sulfonate in the dispersant is 8:3:2. The stirring and neutralization time in the twin-screw mixer is 30 minutes, and the pH value of the neutralized tailings blend is 11.

[0089] In step (5), the neutralized tailings mixture was tested and found to contain Si = 15.2%, Ca = 28.5%, K2O = 4.8%, and Mg = 3.5% by mass percentage. The content of each nutrient met the standard requirements, and no additional additives were needed.

[0090] Testing revealed that the soil conditioner prepared in this embodiment met the Type I standard in GB / T36207-2018 in terms of silicon, calcium, potassium, and magnesium content, had a single particle compressive strength of 14N, and the heavy metal leaching amount was below the standard limit.

[0091] For those skilled in the art, various corresponding changes and modifications can be made based on the above technical solutions and concepts, and all such changes and modifications should be included within the protection scope of the claims of this invention.

Claims

1. A method for preparing a soil conditioner using sulfur-containing tailings, characterized in that, Includes the following steps: (1) Screening and fine grinding: The sulfur-containing tailings are screened, and the undersize material enters the fine grinding system for grinding, with the output particle size controlled to be ≤0.15mm. The oversize material is returned for crushing and then screened again. (2) Aging treatment: After the sulfur-containing tailings that have been finely ground by the fine grinding system are thoroughly mixed with calcium oxide, sodium hydroxide, dolomite powder and potassium feldspar powder, water is added to the resulting tailings mixture, the mixture is stirred evenly and then left to stand for aging, then air-dried, and then placed in an oven to dry, and finely ground to a particle size of less than 0.15 mm. (3) High-temperature activation and flue gas absorption: The tailings mixture obtained from the aging process in step (2) is fed into a rotary kiln for calcination. The generated flue gas enters a plate heat exchanger through a Venturi scrubber to wash the flue gas dust and reduce the flue gas temperature. Then, the flue gas is sequentially fed into a sieve plate absorption tower and a packed tower. In the sieve plate absorption tower and the packed tower, sulfur dioxide is oxidized and absorbed by spraying a spraying liquid onto the flue gas. The absorbent obtained after the spray liquid interacts with the flue gas is fed into the inclined tube sedimentation tank for settling. The supernatant obtained from the settling is returned to the sieve plate absorption tower and the packed tower as absorbent for recycling. The sludge generated from the settling is dewatered by filter press. The solid obtained from the filter press is tested for heavy metal content. Under the condition that it does not exceed the required limit, the solid obtained from the filter press is mixed with the calcined tailings mixture to obtain the tailings mixture. The filtrate obtained from the filter press is mixed with the discharged supernatant to form an acid solution. (4) Activation and neutralization of tailings: The acid solution produced in step (3) is mixed with potassium dihydrogen phosphate and reacted. Then a dispersant is added and stirred. After that, the tailings mixture obtained in step (3) is added and stirred to neutralize, so as to obtain the neutralized tailings mixture. (5) Formulation and Granulation: The neutralized tailings mixture obtained in step (4) is tested and compared for effective silicon, calcium, potassium and magnesium elements. One or more of diatomaceous earth, potassium chloride and superphosphate are added as needed and mixed evenly. Then, a composite disintegrant is added to the mixture, granulated and shaped, and then dried and sieved to obtain the soil conditioner product.

2. The method according to claim 1, characterized in that, In step (2), the solid-liquid mass ratio of the tailings mixture to water is 1:0.8-1:1.

5. After adding water to the tailings mixture, stir it at 20-60℃ for 1-2 hours, let it stand and age for 24-48 hours, and then let it air dry naturally until the moisture content is below 10%.

3. The method according to claim 1, characterized in that, In step (2), the amount of calcium oxide added is 10%-40% of the mass of the finely ground sulfur-containing tailings, the amount of sodium hydroxide added is 5%-20% of the mass of the finely ground sulfur-containing tailings, the amount of dolomite powder added is 5%-20% of the mass of the finely ground sulfur-containing tailings, and the amount of potassium feldspar powder added is 5%-20% of the mass of the finely ground sulfur-containing tailings; the fineness of the dolomite powder is ≤0.15mm, and the fineness of the potassium feldspar powder is ≤0.15mm.

4. The method according to claim 1, characterized in that, In step (3), the fresh spray liquid contains 20-25% H2O2 and 0.01%-0.05% phosphoric acid by mass percentage.

5. The method according to claim 1, characterized in that, In step (3), the calcination temperature is 800-1100℃, the calcination time is 1-2h, and the excess air coefficient is controlled at 1.2-1.5; the inlet flue gas velocity of the Venturi scrubber is controlled at 20-30m / s, the waste liquid containing coarse dust generated by the scrubbing is introduced into the inclined tube sedimentation tank, the supernatant in the inclined tube sedimentation tank is returned to the Venturi scrubber for water replenishment, and the bottom sludge in the inclined tube sedimentation tank is mixed with the sludge generated by the inclined tube sedimentation tank and then filtered together; the inlet flue gas temperature of the sieve plate absorption tower is controlled at 60-80℃, and the liquid-to-gas ratio in the sieve plate absorption tower is 3-5L / Nm 3 The liquid-to-gas ratio in the packed tower is 1-2 L / Nm³. 3 The pH of the spray solution is maintained at 2.5-3.5; the amount of solids obtained by pressure filtration is 5% of the dry weight of the calcined tailings mixture.

6. The method according to claim 1, characterized in that, In step (3), when the sulfuric acid concentration in the supernatant reaches 30%-35% in the inclined tube sedimentation tank, 10%-30% of the supernatant volume is discharged, and the loss of supernatant is replenished with fresh spray liquid.

7. The method according to claim 1, characterized in that, In step (4), the molar ratio of sulfuric acid to potassium dihydrogen phosphate in the acid solution is 0.8-1.2:1, and the reaction temperature of the acid solution and potassium dihydrogen phosphate is 60℃-80℃; the amount of dispersant added is 0.5%-1% of the mass of the tailings mixture, and the dispersant is composed of sodium hexametaphosphate, sodium polyacrylate and lignin sulfonate, with a mass ratio of sodium hexametaphosphate, sodium polyacrylate and lignin sulfonate of (5-8):(1-3):(1-2); the pH value of the neutralized tailings mixture is between 8 and 11.

8. The method according to claim 1, characterized in that, In step (5), assuming the test results of the neutralized tailings admixture, the mass percentages of Si, Ca, K2O, and Mg are a, b, c, and d respectively, then: Based on the purity requirements of the added diatomaceous earth (SiO2 mass percentage ≥ 85%, Si percentage 46.7%), the mass percentage of diatomaceous earth in the final soil conditioner product is calculated using the following formula: If a≥9, then the amount of diatomaceous earth added is 0; Based on the assumption that the potassium content in the added potassium chloride, converted to K2O, is ≥60% by mass, the mass percentage of potassium chloride in the final soil conditioner product is calculated using the following formula: If c≥3, then the amount of potassium chloride added is 0; Based on the conversion of Ca and Mg in the added superphosphate into CaO and MgO, with CaO mass percentage ≥25% and MgO mass percentage ≥1%, and Ca conversion coefficient 0.714 and Mg conversion coefficient 0.833, the mass percentage of superphosphate in the final soil conditioner product is calculated using the following formula: If b≥20 and d≥2, then the amount of superphosphate added is 0.

9. The method according to claim 1, characterized in that, In step (5), after granulation, the soil conditioner product with a particle size of 2-4 mm is obtained by drying at 60-80℃ for 30-60 min and then cooling in a sulfurized bed for 10-30 min.

10. The method according to claim 1, characterized in that, In step (5), the amount of compound disintegrant added is 0.5%-1.5% of the total mass of the mixture. The compound disintegrant includes bentonite, pregelatinized starch, sodium carboxymethyl starch and citric acid residue. The mass ratio of bentonite, pregelatinized starch, sodium carboxymethyl starch and citric acid residue is (3-5):(1-2):(0.5-1):(1-2). First, dry mix bentonite and citric acid residue for 3-6 minutes, then add pregelatinized starch and sodium carboxymethyl starch and mix for 5-10 minutes, and then mix with the mixture. Granulation is carried out by disc or extrusion granulation, and the proportion of particles with a diameter of 2-4 mm is ≥80%. The moisture content of the dried output is controlled within 8%. The dried output is screened by 2 mm and 4 mm double-layer screens. The fine powder under the screen with a particle size <2 mm is returned to participate in granulation, and the coarse particles on the screen with a diameter >4 mm are crushed and returned to participate in granulation.

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