Method for preparing slow-release silicon fertilizer based on magnetic separation of coal gangue

Abstract

The invention discloses a method for preparing a slow-release silicon fertilizer based on magnetic separation of coal gangue, which comprises the following steps: S1, carrying out acid-alkali pretreatment on coal gangue to obtain filter residues, and carrying out magnetization treatment to obtain magnetized coal gangue powder; s2, mixing with water to obtain slurry, and removing iron impurities through primary magnetic separation, activating treatment and secondary magnetic separation to obtain slurry subjected to wet magnetic separation; s3, fixing an active silicon structure through a water quenching method after cooling, and filtering, drying and crushing to obtain the slow-release silicon fertilizer. And S4, after the iron impurities removed in the S2 are subjected to acid pickling activation, Fe3O4 is prepared through a coprecipitation method, and after magnetic separation, washing and drying, the Fe3O4 is used for magnetization treatment of the filter residues in the S1. The method can improve the purity and slow release performance of the silicon fertilizer prepared from the coal gangue as the raw material, is also beneficial to improving the recovery rate of the coal gangue treatment process, and has the characteristics of low treatment cost, energy conservation and environmental protection.

Description

Technical Field

[0001] The invention belongs to the technical field of slow-release silicon fertilizer preparation, and in particular relates to a method for preparing slow-release silicon fertilizer based on magnetization and magnetic separation of coal gangue. Background Art

[0002] Gangue is a solid waste generated during the construction of coal mines, development and excavation, coal mining and coal washing. Its dry ash content is greater than 50%, its carbon content is low, its texture is hard and it is black-gray. It is an inevitable by-product of coal production and processing, and its annual emission is usually equivalent to about 10% of the coal production of the year. Gangue can be divided into two categories according to its state: original gangue and spontaneous combustion gangue: the appearance of original gangue is mostly black or gray-black, and coal slime and fine particles are often attached to the surface; spontaneous combustion gangue may spontaneously combust due to the increase in internal temperature, and its carbon content is low, its porosity is high, and its surface is mostly pottery red or pottery yellow. The inside may appear black due to incomplete combustion. The chemical composition of gangue mainly includes Al2O3, SiO2 and C, followed by CaO, Fe2O3, MgO, etc. The mineral composition is mainly kaolin, hydromica, bauxite and carbon.

[0003] As solid waste generated during coal mining and washing, long-term storage and improper treatment of coal gangue will bring a series of serious environmental, economic and social hazards, which are specifically reflected in the following aspects:

[0004] a. The carbon and sulfide remaining in the gangue may spontaneously combust under suitable conditions, releasing a large amount of harmful gases, such as sulfur dioxide (SO2), carbon monoxide (CO), nitrogen oxides (NO x ) etc., causing air pollution and even forming acid rain, which harms human health and the ecological environment.

[0005] b. Coal gangue contains heavy metals (such as lead, cadmium, mercury, etc.) and harmful chemicals, which may seep into groundwater or surface water under the erosion of rainwater, pollute water sources, and endanger aquatic ecosystems and human drinking water safety.

[0006] c. The storage of coal gangue requires a large amount of land resources, especially in coal producing areas where land resources are already scarce. Long-term storage not only wastes land, but may also damage surface vegetation and lead to land desertification.

[0007] d. Gangue dumping will cover the surface vegetation, destroy the balance of the ecosystem, and lead to a decline in biodiversity. At the same time, the surface structure of the gangue dumping site is unstable, which is prone to cause soil erosion and aggravate the risk of geological disasters.

[0008] Silicon fertilizer is a new type of fertilizer. As the fourth major fertilizer element, silicon has attracted much attention in the international soil community, second only to nitrogen, phosphorus, and potassium. It is particularly suitable for crops with high silicon requirements such as rice, wheat, corn, and sugarcane. Rice is known as a "silicic acid plant" due to its high demand for silicic acid. Applying silicon fertilizer can not only enhance its disease resistance and drought resistance, but also strengthen the stem strength, promote photosynthesis, increase the seed setting rate, and accelerate the accumulation of dry matter, thus significantly increasing the yield. Research shows that the application of silicon fertilizer can increase the yield of rice by 10% - 20%, wheat by 10% - 15%, peanuts by 15% - 35%, soybeans by 10% - 20%, sugarcane by 10% - 25%, corn by 12% - 20%, and vegetables by 12% - 20%, with very significant economic benefits.

[0009] At present, there are already various research results on silicon fertilizer production technology and preparation processes, but there has not yet been a process for preparing silicon fertilizer from coal gangue that simultaneously utilizes magnetization and magnetic separation technologies. In CN202210977182.2, a coal gangue magnetization soil conditioner and its preparation method mainly innovates in magnetization treatment, and CN101328091A iron ore tailings magnetization slow-release mineral fertilizer only includes magnetization treatment.

[0010] Therefore, a process is needed that can improve the recovery rate of coal gangue without reducing the purity and slow-release performance of silicon fertilizer. Summary of the Invention

[0011] Technical problems to be solved: In response to the above technical problems, the present invention provides a method for preparing slow-release silicon fertilizer based on magnetized and magnetic-separated coal gangue, which can not only improve the purity and slow-release performance of silicon fertilizer prepared from coal gangue, but also help improve the recovery rate of the coal gangue treatment process, and has the characteristics of low treatment cost, energy conservation, and environmental protection.

[0012] Technical solution: A method for preparing slow-release silicon fertilizer based on magnetized and magnetic-separated coal gangue includes the following steps:

[0013] S1. Pretreat the coal gangue with acid and alkali to obtain filter residue, and magnetize the filter residue to obtain magnetized coal gangue powder;

[0014] S2. After mixing the magnetized coal gangue powder with water to form a slurry, perform primary magnetic separation, activation treatment, and secondary magnetic separation to remove iron impurities and obtain the slurry after wet magnetic separation;

[0015] S3. Cool the slurry after wet magnetic separation and fix the active silicon structure by the water quenching method. After filtration, drying, and pulverization, the slow-release silicon fertilizer is obtained and stored in a vacuum;

[0016] S4. After pickling and activating the iron impurities removed in S2, prepare Fe3O4 by the coprecipitation method, and use it for the magnetization treatment of the filter residue in S1 after magnetic separation, washing, and drying.

[0017] Preferably, the S1 includes:

[0018] S1.1. Mix the coal gangue filter residue obtained by acid-base pretreatment with a solution containing Fe 2+ salt and Co 2+ salt, adjust the pH to 8.0 ± 0.2, then separate the solid coal gangue filter residue by filtration and remove the residual moisture to obtain dry coal gangue powder containing magnetic substances;

[0019] S1.2. After ultrasonic treatment of the coal gangue powder containing magnetic substances, age it in absolute ethanol, and obtain magnetized coal gangue powder after filtration and drying.

[0020] Further, in the S1.2, the frequency of ultrasonic treatment is 1000 Hz.

[0021] Further, in the S1.2, the aging time is 24 h, and the drying method is drying by blowing air at 105 °C.

[0022] Preferably, the S2 includes:

[0023] S2.1. Mix the magnetized coal gangue powder with water to form a slurry without particle agglomeration;

[0024] S2.2. Remove strongly magnetic iron minerals with a magnetic field strength of 0.8 - 1.2 T, and further remove non-target weakly magnetic iron impurities with a magnetic field strength of 1.5 - 2.0 T to obtain a slurry after primary magnetic separation;

[0025] S2.3. Use CaCO3, Na2CO3, and NaOH with a mass ratio of 1:0.1:0.05 as activators, mix them with the slurry after primary magnetic separation, dry to a moisture content ≤ 2%, and then activate at a high temperature of 700 ± 10 °C for 2 h to obtain a calcined product after activation treatment;

[0026] S2.4. After mixing the calcined product with water, remove iron impurities through wet grinding and wet magnetic separation to obtain a slurry after wet magnetic separation.

[0027] Further, in the S2.1, the mass ratio of magnetized coal gangue powder to water for mixing is 1:3.

[0028] Further, in the S2.2, the iron content in the solid of the slurry after primary magnetic separation is ≤ 3 wt%.

[0029] Further, in the S2.4, the concentration after mixing the calcined product with water is 40 wt%, the particle size of wet grinding is D90 ≤ 10 μm (the particle size of 90% of the particles is less than or equal to 10 microns), and the magnetic field strength of wet magnetic separation is 0.5 T.

[0030] Preferably, in S3, the water-to-material ratio of the water quenching method is 3:1, dried by a spray drying tower, crushed by an air flow mill, and the fineness of the slow-release silicon fertilizer is 200 mesh.

[0031] Preferably, S4 includes:

[0032] S4.1. Pickle the iron impurities removed in S2 with a hydrochloric acid solution with pH < 3, activate with Na2S2O4 as a reducing agent, and reduce Fe 3+ to Fe 2+ , evaporate and concentrate the pickled and activated solution to obtain solid salts of Fe 2+ and Fe 3+ ;

[0033] S4.2. Mix the obtained solid salts of Fe 2+ and Fe 3+ in a mass ratio of 1:2, dissolve in water, dropwise add ammonia water and stir vigorously to generate Fe3O4 precipitate;

[0034] S4.3. Magnetically separate the precipitate, wash it with pure water until neutral, dry it at 105 °C, and use it for the magnetization treatment of the filter residue in S1.

[0035] Beneficial effects: Through simple magnetization, magnetic separation and activation processes, the present invention converts low-value coal gangue into high-value silicon fertilizer, with significant economic benefits.

[0036] The iron impurities separated by magnetic separation in the present invention are regenerated into Fe3O4 nanoparticles and recycled for the magnetization process, forming a closed-loop cycle system, reducing the waste of iron resources, lowering the raw material cost, and further enhancing the economy.

[0037] The present invention combines Fe 2+ / Co 2+ co-precipitation with ethanol aging process to precisely control the formation of magnetic oxides and the stability of magnetic domains, improving the magnetic separation efficiency and providing a new idea for the efficient separation of coal gangue.

[0038] The present invention adopts wet magnetic separation and high-temperature activation processes, avoiding the use of a large amount of strong acids and alkalis in traditional chemical treatments, reducing the emissions of waste water and waste gas, and conforming to the concept of green manufacturing. The gradient magnetic field separation combined with the high-temperature activation process realizes the deep removal of iron impurities (≤3%) and the maximum release of silicon activity, providing technical guarantee for the efficient preparation of silicon fertilizer.

[0039] The present invention fixes the active silicon structure by water quenching and combines with an ultra-fine grinding process (200 mesh) to make the silicon fertilizer slowly release in the soil, extend the fertilizer efficiency, reduce the fertilization frequency, and lower the agricultural cost. Description of the Drawings

[0040] Figure 1 This is the process schematic diagram of the present invention. Specific embodiments

[0041] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0042] Example 1

[0043] A method for preparing slow-release silicon fertilizer from magnetized coal gangue by magnetic separation includes the following steps:

[0044] S1. Pretreat the coal gangue with acid and alkali to obtain filter residue, and magnetize the filter residue to obtain magnetized coal gangue powder:

[0045] S1.1. Mix 100 g of the coal gangue filter residue obtained by acid and alkali pretreatment with ferrous sulfate solution with a solute mass of 10 g and cobalt chloride solution with a solute mass of 1 g, adjust the pH to 8.0 ± 0.2 with ammonia water, react for 2 h, and the metal ions Fe 3 + forms magnetic composite oxides. Subsequently, filter and separate the solid coal gangue filter residue, and remove the residual moisture to obtain dry coal gangue powder containing magnetic substances;

[0046] S1.2. Place the coal gangue powder containing magnetic substances in a magnetic stirrer, ultrasonically treat it at a frequency of 1000 Hz for 30 min, then age it at room temperature in 200 mL of absolute ethanol for 24 h to stabilize the magnetic domain structure through the directional arrangement of solvent molecules. After filtration, dry it in a blast dryer at 105 °C for 2 h to obtain magnetized coal gangue powder. The formation rate of magnetic composite oxides (Fe3O4, Fe2O3·FeO) is ≥ 95%, and the specific saturation magnetization intensity of the magnetized coal gangue powder is 45 emu / g;

[0047] S2. After mixing the magnetized coal gangue powder with water to form a slurry, perform primary magnetic separation, activation treatment, and secondary magnetic separation to remove iron impurities and obtain the slurry after wet magnetic separation:

[0048] S2.1. Mix the magnetized coal gangue powder with water at a mass ratio of 1:3 to form a slurry without particle agglomeration;

[0049] S2.2. Set the magnetic field intensity of the magnetic separator to 1.0 T to remove strongly magnetic iron minerals, and then further remove non-target weakly magnetic iron impurities at a magnetic field intensity of 1.8 T to obtain the slurry after primary magnetic separation; after primary magnetic separation, the iron mass fraction in the coal gangue solid in the slurry drops from 8.5% to 2.8%;

[0050] S2.3. Mix 10 g of CaCO3, 1 g of Na2CO3, and 0.5 g of NaOH as an activator, and mix it with the solids in the slurry after primary magnetic separation at a mass ratio of 10:1. Dry it to a moisture content of ≤2%, and then calcine it at a high temperature of 700 °C in a rotary kiln for 2 h to dissociate the silicon-aluminum mineral structure and convert it into active silicate, obtaining the calcined product after activation treatment; the effective silicon content in the calcined product after activation, i.e., the dehydrated solid, is 25.3%, and the dissociation rate of silicon-aluminum minerals is ≥90%;

[0051] S2.4. After mixing the calcined product with deionized water at a mass ratio of 1:1.5, wet-grind it to D90 ≤ 10 μm. Remove residual trace iron impurities by secondary wet magnetic separation, and set the magnetic field intensity of the magnetic separator to 0.5 T to obtain the slurry after wet magnetic separation. After secondary magnetic separation, the iron content is further reduced to 0.8%, meeting the requirement of ≤3%;

[0052] S3. After quickly cooling the slurry after secondary magnetic separation to room temperature, use the water quenching method with a water-to-material ratio of 3:1 to fix the active silicon structure, and obtain the wet silicon fertilizer with a moisture content of about 30% through filtration. Feed the wet material into a spray drying tower, with an inlet temperature of 200 °C and an outlet temperature of 80 °C, and dry it to a moisture content of ≤5%. Use an air-flow pulverizer to pulverize the dried product to 200 mesh to obtain the powdered slow-release silicon fertilizer. Vacuum-pack the finished silicon fertilizer in a plastic bag and store it in a cool and dry place;

[0053] Finally, the moisture content of the finished silicon fertilizer is 4.8%, meeting the requirement of ≤5%. The fineness of the silicon fertilizer is 200 mesh, and it has good fluidity, facilitating application; the effective silicon content in the silicon fertilizer is 25.3%, and it has excellent slow-release performance (the cumulative release rate reaches 85% in 30 days);

[0054] S4. After pickling and activating the iron impurities removed in S2, prepare Fe3O4 by the co-precipitation method, and use it for the magnetization treatment of the filter residue in S1 after magnetic separation, washing, and drying:

[0055] S4.1. Take 10 g of the iron impurities removed in S2, add 100 mL of hydrochloric acid solution with pH = 2, use 1 g of sodium dithionite Na2S2O4 as a reducing agent for activation, stir at room temperature for 30 min, and reduce Fe 3+ to Fe 2+ , improve the solubility of iron and remove the oxide layer. The reduction rate of Fe 3+ in the iron impurities is 98%, and the removal rate of Fe2O3 is ≥95%; the reaction is as follows:

[0056]

[0057] Subsequently, evaporate and concentrate the solution after pickling and activation to obtain the solid salts of Fe 2+ and Fe 3+ ;

[0058] S4.2. Weigh 6.500 g of FeSO4·7H2O and 7.462 g of FeCl3, dissolve them in 200 mL of deionized water, slowly add 50 mL of 25% ammonia water dropwise at 25 °C and stir vigorously for 10 minutes to form Fe3O4 precipitate. The reaction is as follows:

[0059] Fe 2+ + 2Fe 3+ + 8OH - → Fe3O4↓ + 4H2O;

[0060] S4.3. Magnetically separate the precipitate, wash it with pure water until it is neutral, dry it at 105 °C for 2 h, and obtain Fe3O4 nanoparticles, which are used for the magnetization treatment of the filter residue in the next batch of coal gangue S1. The prepared Fe3O4 nanoparticles have a particle size of 20 - 50 nm and a specific saturation magnetization of 65 emu / g, meeting the requirements for recycling.

Claims

1. A method for preparing slow-release silicon fertilizer from magnetized coal gangue, characterized in that, It includes the following steps: S1. Pretreat the coal gangue with acid and alkali to obtain filter residue, and magnetize the filter residue to obtain magnetized coal gangue powder; S2. After mixing the magnetized coal gangue powder with water to form a slurry, conduct primary magnetic separation, activation treatment and secondary magnetic separation to remove iron impurities, and obtain the slurry after wet magnetic separation; S3. Cool the slurry after wet magnetic separation, fix the active silicon structure by the water quenching method, and obtain the slow-release silicon fertilizer after filtration, drying and pulverization, and store it in vacuum; S4. After pickling and activating the iron impurities removed in S2, prepare Fe3O4 by the co-precipitation method, and use it for the magnetization treatment of the filter residue in S1 after magnetic separation, washing and drying.

2. The method for preparing slow-release silicon fertilizer based on magnetized magnetic separation coal gangue according to claim 1, wherein The S1 includes: S1.

1. Mix the coal gangue filter residue obtained by acid-base pretreatment with a solution containing Fe 2+ salt and Co 2+ salt, adjust the pH to 8.0 ± 0.2, then filter and separate the solid coal gangue filter residue, and remove the residual moisture to obtain dry coal gangue powder containing magnetic substances; S1.

2. Ultrasonically treat the coal gangue powder containing magnetic substances, age it in absolute ethanol, and obtain magnetized coal gangue powder after filtration and drying.

3. The method for preparing slow-release silicon fertilizer based on magnetized magnetic separation coal gangue according to claim 2, characterized in that, In the S1.2, the ultrasonic treatment frequency is 1000 Hz.

4. A method for preparing slow-release silicon fertilizer based on magnetized magnetic separation coal gangue according to claim 2, characterized in that, In the S1.2, the aging time is 24 h, and the drying method is drying in a blast dryer at 105 °C.

5. A method for preparing slow-release silicon fertilizer based on magnetized magnetic separation coal gangue according to claim 1, characterized in that, The S2 includes: S2.

1. Mix the magnetized coal gangue powder with water to form a slurry without particle agglomeration; S2.

2. Remove strongly magnetic iron minerals with a magnetic field intensity of 0.8 - 1.2 T, and further remove non-target weakly magnetic iron impurities with a magnetic field intensity of 1.5 - 2.0 T to obtain the slurry after primary magnetic separation; S2.

3. Use CaCO3, Na2CO3, and NaOH with a mass ratio of 1:0.1:0.05 as activators, mix them with the slurry after primary magnetic separation, dry to a moisture content ≤ 2%, and then conduct high-temperature activation at 700 ± 10 °C for 2 h to obtain the calcined product after activation treatment; S2.

4. After mixing the calcined product with water, conduct wet grinding and wet magnetic separation to remove iron impurities, and obtain the slurry after wet magnetic separation.

6. The method for preparing slow-release silicon fertilizer based on magnetized magnetic separation coal gangue according to claim 5, characterized in that In the S2.1, the mass ratio of the magnetized coal gangue powder to water is 1:

3.

7. A method for preparing slow-release silicon fertilizer based on magnetized magnetic separation coal gangue according to claim 5, characterized in that, In the S2.2, the iron content in the solid of the slurry after primary magnetic separation is ≤ 3 wt%.

8. A method for preparing slow-release silicon fertilizer based on magnetized magnetic separation coal gangue according to claim 5, characterized in that, In the S2.4, the concentration after mixing the calcined product with water is 40 wt%, 90% of the particle size D90 after wet grinding is ≤ 10 μm, and the magnetic field intensity of wet magnetic separation is 0.5 T.

9. A method for preparing slow-release silicon fertilizer based on magnetized magnetic separation coal gangue according to claim 1, characterized in that, In the S3, the water-to-material ratio of the water quenching method is 3:1, dry through a spray drying tower, pulverize through an air flow pulverizer, and the fineness of the slow-release silicon fertilizer is 200 mesh.

10. A method for preparing slow-release silicon fertilizer based on magnetized magnetic separation coal gangue according to claim 1, characterized in that, The S4 includes: S4.

1. Pickle the iron impurities removed in S2 with a hydrochloric acid solution with pH < 3, activate it with Na2S2O4 as a reducing agent, and reduce Fe 3+ to Fe 2+ . Evaporate and concentrate the pickled and activated solution to obtain solid salts of Fe 2+ and Fe 3+ ; S4.

2. The obtained Fe 2+ and Fe 3+ solid salts are mixed at a mass ratio of 1:2, dissolved in water, and ammonia water is added dropwise with vigorous stirring to form Fe3O4 precipitate; S4.

3. Conduct magnetic separation to separate the precipitate, wash it with pure water until neutral, dry it at 105 °C, and use it for the magnetization treatment of the filter residue in S1.

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