Preparation method of low-temperature humified coal gangue-agriculture and forestry solid waste porous slow-release humic acid water-soluble fertilizer

Abstract

According to the preparation method of the low-temperature humified coal gangue-agriculture and forestry solid waste porous slow-release humic acid water-soluble fertilizer, the coal gangue is subjected to magnetic separation and flotation to remove impurities, then the composite chlorinating agent is used for low-temperature chlorination, heavy metal is effectively removed, and meanwhile energy consumption and environmental risks are reduced. Then, under a controlled low-temperature condition, through microwave assistance and specific atmosphere adjustment, a humification reaction is triggered, meanwhile, formation of a porous structure of the material is triggered, and the water solubility and the slow release effect of the fertilizer are enhanced. According to the method, the resource utilization rate of the coal gangue is increased, the high-efficiency soil conditioner is effectively generated through an innovative low-temperature treatment process, and good environmental protection benefits and economic values are achieved. Through the structural design of the obtained fertilizer, the fertilizer can respond to environmental factors, the nutrient release rate is automatically adjusted, and plant absorption and soil health are optimized.

Description

Technical Field

[0001] The present invention relates to the technical field of solid waste resource utilization and environmental protection, and particularly relates to a preparation method of a porous slow-release humic acid water-soluble fertilizer from coal gangue and agricultural and forestry solid wastes by low-temperature humification. Background Art

[0002] As the main solid waste in the process of coal mining and washing, the resource utilization of coal gangue has long faced technical bottlenecks such as heavy metal pollution, dense structure, and single function.

[0003] Although existing patented technologies have made breakthroughs in some aspects, they are mostly limited to single treatment objectives or high-energy-consuming processes, which are specifically manifested in the following aspects. First, there is a contradiction between the heavy metal removal efficiency and energy consumption. The traditional high-temperature chlorination method (such as CN200910088888.X) requires a high temperature of 900 - 1100 °C, with high energy consumption and a high risk of chlorine escape, and there are potential hazards in the heavy metal removal technology. The physical / chemical solidification technology (such as CN119285284A) only stabilizes heavy metals through a solidifying agent, without achieving deep removal, and there are still environmental hazards in the long term; moreover, the exploration of low-temperature processes is insufficient. Existing technologies such as CN202410669128.0 propose a mixed sludge-improved substrate, but rely on single pyrolysis and do not integrate the chlorination detoxification link, and heavy metal residues are likely to cause secondary pollution. Second, the resource conversion efficiency and functional design are not comprehensive. This technology relies on superabsorbent resins to retain water, with a low humic acid yield (≤15%) and disordered pores, unable to achieve the coordination of nutrient slow release and air permeability. At the same time, the process lacks intelligence, and there are limitations in structure regulation. For example, CN119287088A promotes slag-metal separation through steel slag tempering, but does not construct a porous humified structure, and the silicon-aluminum components of coal gangue are not effectively combined with organic matter, resulting in a short slow-release period (<30 days). At the same time, there are defects in the intelligence and environmental protection of the process. CN115063659B improves the detection accuracy of coal gangue through the fusion of multiple characteristic layers, but does not form a closed-loop linkage with the treatment process, unable to dynamically optimize reaction parameters; the control of secondary pollution is weak, unable to adjust reaction parameters in real time, and the industrial adaptability is poor. Finally, the control of secondary pollution is insufficient. The treatment of chlorination tail gas is not thorough (Cl2 residue ≥ 5%), and the water washing process is extensive (Cl- residue ≥ 1%), which is likely to cause soil salinization. For example, the screening device of CN222241351U improves the dust prevention effect, but does not involve the problems of Cl2 tail gas and Cl - residue in chemical treatment, and the environmental protection is insufficient. CN119056843A improves the crushing efficiency through waste heat utilization, but does not achieve a full-process heat energy closed loop, the heat energy recovery is extensive, and there is a lack of design for in-depth treatment of pollutants.

[0004] In summary, the existing technologies generally suffer from high energy consumption, single function, lack of intelligence, and the risk of secondary pollution, making it difficult to meet the integrated requirements of "detoxification - resource utilization - functionalization". For example, the high-temperature chlorination and solidification technologies focus on a single link, the humification process ignores structural regulation, and the detection technology lacks closed-loop feedback.

[0005] Therefore, it is urgent to develop an innovative system that deeply integrates low-temperature synergy, porous humification, and intelligent regulation to break through the traditional technical barriers and achieve the efficient value-added utilization of coal gangue. Summary of the Invention

[0006] The present invention discloses a preparation method of a porous slow-release humic acid water-soluble fertilizer from coal gangue - agricultural and forestry solid wastes based on low-temperature humification, belonging to the fields of solid waste resource utilization and environmental protection technologies. Aiming at problems such as heavy metal pollution in coal gangue, low utilization rate of agricultural and forestry solid wastes, and single function of traditional fertilizers, the present invention breaks through three major technical bottlenecks of low-temperature efficient detoxification - directional synthesis of humic acid - multi-stage pore synergistic regulation through innovative process design, and realizes the deep coupling of harmless treatment, resource utilization, and functional value-added utilization of solid wastes.

[0007] Specifically, the present invention is a preparation method of a porous slow-release humic acid water-soluble fertilizer from coal gangue - agricultural and forestry solid wastes by low-temperature humification, comprising the following steps:

[0008] Step S1, low-temperature chlorination of coal gangue to remove heavy metals;

[0009] Step S2, section temperature control and gas regulation;

[0010] Step S3, low-temperature humification and construction of porous structure.

[0011] Furthermore, step S1 specifically comprises the following steps:

[0012] Step S11 further includes the operation of pulverizing the pretreated coal gangue; the materials obtained by flotation are first pulverized to a particle size of 50 - 800 mesh to ensure that the fineness of the materials is suitable for subsequent flotation operations. Some materials will be further ultrafinely pulverized to a particle size of ≤1 μm, or the particle size will be refined to ≤100 nm by high-energy ball milling / jet milling methods to obtain nano-scale particles, and the proportion of ultrafine pulverization is 10% - 20%.

[0013] Further, in step S11, the cationic flotation agent is a quaternary ammonium salt flotation agent, selected from one of oleic acid amide and dimethylaminoethyl dimethylaniline, and the concentration of the cationic flotation agent is controlled between 0.1 and 1 mol / L. Its function is to combine with the surfaces of impurity minerals such as silicon minerals and aluminum minerals in coal gangue, making them lipophilic and enabling them to combine with bubbles and float to the foam layer. The specific dosage of the reagent is adjusted according to the mineral composition of the ore and the requirements of the flotation effect. The dosage of the inhibitor is relatively small, usually between 0.05 and 0.2 mol / L, and is used to inhibit the flotation behavior of some minerals such as clay minerals to ensure that only the target minerals are flotated. The concentration of the foaming agent is usually controlled between 0.01 and 0.1 mol / L.

[0014] Step S12, prepare composite chloride A by mixing alkaline earth metal chloride and alkali metal chloride; the alkaline earth metal chloride is selected from one of MgCl2 and CaCl2, the alkali metal chloride is selected from one of NaCl and KCl, and the mixing mass ratio is 1:(0.05 - 0.5);

[0015] Step S13, mix the composite chloride A prepared in step S12 with the coal gangue pretreated in step S11; the addition amount of the composite chloride A accounts for 5 - 30% of the mass of the coal gangue.

[0016] Further, the mixing method in step S13 is selected from one of dry mixing, wet impregnation mixing, and fluidized bed spraying mixing. The addition amount of the composite chloride A accounts for 5 - 30% of the mass of the coal gangue; when dry mixing is adopted, it is mixed in a V - type mixer or a double - screw ribbon mixer, and the mixing time is 10 - 30 minutes, and the mixing uniformity error does not exceed ±2%; when wet impregnation is adopted, the composite chloride A is prepared into an aqueous solution with a concentration of 0.1 - 3 mol / L, the liquid - solid ratio is 1 - 3 mL / g, and it is impregnated at 25 - 50 °C for 30 - 120 minutes; when fluidized bed spraying is adopted, the bed temperature is 40 - 80 °C, the spray particle size is 50 - 200 μm, the spraying rate is 0.5 - 2 mL / min, the intake air speed is 0.1 - 0.5 m / s, and the spraying time is 10 - 60 minutes for mixing.

[0017] Further, step S2 specifically includes the following steps:

[0018] Step S21, pre - activation stage, heat to a certain temperature range at a certain heating rate, and simultaneously introduce a mixed gas of Cl2 and N2 and / or O2.

[0019] Step S22, deep removal stage: Load the material obtained in step S13 into a closed reaction device, and control the temperature gradient of the material. The reaction device is provided with multiple temperature control zones, preferably 2 - 5 temperature control segments. The temperature gradient of the material is precisely controlled through the interlayer heat-conducting oil circulation system. During the heating process, chlorine gas with a purity ≥ 99% is continuously introduced. The chlorine-containing tail gas is recycled and absorbed by the NaOH solution. The processed material is the heavy metal-removed coal gangue B.

[0020] Step S23, cooling and post-treatment: Cool the heavy metal-removed coal gangue B obtained in step S22 from the high-temperature state. Immediately after the cooling step, the coal gangue B is subjected to multi-stage water washing treatment. Finally, the washed coal gangue C is subjected to dechlorination post-treatment to obtain the heavy metal-removed coal gangue D.

[0021] Further, in the mixed gas of Cl2 with N2 and / or O2 in step S21, the proportion of Cl2 is 5 - 40%, the flow rate of the mixed gas is 0.5 - 3 L / min, and it is heated at a heating rate of 5 - 10 °C / min to 150 - 250 °C for 5 - 30 min.

[0022] Further, the control of the temperature gradient in step S22 is specifically as follows: The temperature is gradually increased to 300 - 500 °C at a heating rate of 5 - 10 °C / min. During the heating process, chlorine gas (Cl2) with a purity ≥ 99% is continuously introduced at a flow rate of 2 - 8 L / min, and it is heated at a constant temperature in the target temperature range of 300 - 500 °C for 1 - 4 hours. To ensure the full progress of the chlorination reaction and enable heavy metals such as Pb, Cd, and Cr to fully react with chlorine gas and be removed from the material in the form of volatile chlorides. To ensure the safety of the process and the efficient utilization of resources, the tail gas generated by the reaction passes through a closed tail gas circulation absorption system, and the chlorine-containing tail gas is recycled and absorbed by the NaOH solution with a concentration of 1 - 5 mol / L, thereby realizing the recycling and reuse of chlorine resources. The material processed in this step is the heavy metal-removed coal gangue B.

[0023] Further, the cooling and temperature reduction in step S23 are selected from one of inert gas quenching, liquid nitrogen rapid cooling, and programmed gradient cooling.

[0024] When selecting inert gas quenching, an inert gas Ar or N2 with a purity ≥ 99.99% is introduced into the cooling chamber at a flow rate of 5 - 20 L / min to quickly cool the material to below 50°C, with a cooling rate ≥ 10°C / min, to prevent secondary contamination or unnecessary reactions of the material; when selecting liquid nitrogen rapid cooling, liquid nitrogen is used to quickly cool the material by direct spraying or indirect contact, with a temperature reduction rate ≥ 30°C / min, to rapidly reduce the material temperature to below 30°C to ensure the stability of the material particles and the product purity; when selecting programmed gradient cooling, a temperature control device is used to gradually and orderly reduce the temperature at a rate of 1 - 10°C / min until the material temperature drops to below 50°C to prevent thermal stress damage to the material and maintain the structural integrity and performance stability of the material.

[0025] After the cooling step, coal gangue B is immediately subjected to multi-stage water washing. The water washing process includes: First-stage water washing: Under the condition of a solid-liquid mass ratio of 1:2 - 1:5 (g / mL), the pH value of the washing liquid is adjusted to 2 - 3, stirred and washed for 20 - 60 min, and the temperature is controlled at 20 - 50°C to remove acid-soluble impurities; Second-stage water washing: Continue to adjust the pH of the washing liquid to 5 - 6, with a solid-liquid ratio of 1:2 - 1:5 (g / mL), stirred and washed for 20 - 60 min, and the temperature is 20 - 50°C to further remove neutral soluble impurities; Third-stage water washing: Adjust the pH value of the washing liquid to 7 - 9, stirred and washed for 20 - 60 min, and the solid-liquid ratio is still 1:2 - 1:5 (g / mL), and the temperature is maintained at 20 - 50°C to thoroughly remove residual soluble salts and alkali-soluble impurities.

[0026] Finally, the washed coal gangue C is subjected to post-treatment for dechlorination to obtain deheavy metal coal gangue D. The content of residual chloride ions is further reduced by any of the following methods: When selecting ion exchange resin dechlorination: A strongly basic anion exchange resin is selected for chloride ion exchange, and the resin dosage accounts for 1 - 5% of the mass of the treated material, stirred or statically exchanged for 0.5 - 2 hours, and the temperature is controlled at 20 - 40°C; When selecting electrodialysis dechlorination, the material is subjected to electrodialysis dechlorination treatment for 0.5 - 2 hours at a temperature of 20 - 40°C and an electric field strength of 0.1 - 1 V / cm to further ensure that the residual chloride ions in the product are reduced to the lowest level. After the above steps of treatment, the final dechlorinated and purified high-purity coal gangue product D is obtained, which is suitable for high-value resource utilization.

[0027] Further, step S3 specifically includes the following steps:

[0028] Step S31: Mix the heavy-metal-removed coal gangue D with agricultural and forestry solid waste, add a gradient foaming agent and a redox initiator, and trigger the reaction under microwave ignition and CO2 / N2 atmosphere control; simultaneously generate humic acid and a porous structure, and in-situ load nano-clay / biochar to enhance stability; the reaction atmosphere can also be selected from a CO2 / Ar or CO2 / O2 mixed gas, with a mixing volume ratio of 1:1 - 5; the porosity range is extended to 50 - 90%, and the pore size distribution covers micropores (<2nm), mesopores (2 - 50nm), and macropores (>50nm); the in-situ loaded functional materials include but are not limited to nano-clay (montmorillonite, kaolin), biochar (rice husk charcoal, bamboo charcoal), or metal oxides (Fe3O4, Al2O3), with an addition amount of 1 - 10%.

[0029] The types of agricultural and forestry solid waste include but are not limited to biomass such as straw, fruit shells, wood chips, algae, and mushroom residues, which are crushed to 10 - 100 mesh, and the heavy-metal-removed coal gangue B is mixed with the agricultural and forestry solid waste at a mass ratio of 1:(1 - 5).

[0030] Furthermore, in step S31, the gradient foaming agent is compounded by a low-temperature foaming agent and a high-temperature foaming agent, with a mass ratio of 1:(1 - 4); the redox initiator is a combination of a nitrate and a reducing agent, with a molar ratio of nitrate to reducing agent of 1:(0.2 - 3); the microwave ignition power is 300 - 1500W, the triggering temperature is 180 - 600°C, and the reaction time is 10 - 90 minutes. The low-temperature foaming agent is selected from one of ammonium bicarbonate and citric acid, and the high-temperature foaming agent is selected from one of urea and ammonium carbonate; the nitrate is selected from one of NaNO3 and NH4NO3, and the reducing agent is selected from one of glucose and lignosulfonate;

[0031] Furthermore, the reaction product obtained in step S31 is initially crushed to a particle size of 2 - 5mm by a roller crusher or a jaw crusher, then further crushed to 50 - 200 mesh by a hammer mill or a high-speed impact mill, and finally refined into uniform particles with a particle size of 200 - 800 mesh by an ultrafine air-flow mill.

[0032] The specific method for in-situ loading nano-clay / biochar in step S31:

[0033] When the dry mixing loading method is selected, the functional material is pre-ground into nano- or sub-micron-sized particles (particle size 10–500 nm), and directly mixed with the materials in powder form under stirring conditions. The addition amount is 1–10% of the total mass of the materials, and the stirring time is 10–30 min to ensure uniform mixing of the functional material particles with coal gangue and agricultural and forestry solid wastes, realizing physical intercalation or surface adhesion between solids. When the wet impregnation loading method is selected, the functional material is configured into a suspension with a concentration of 0.1–5 wt%. A small amount of surfactant (such as sodium dodecyl sulfate, 0.01–0.1%) can be added to the suspension. At 25–60 °C, impregnation treatment is carried out at a liquid-solid ratio of 1–3 mL / g, and ultrasonic or mechanical stirring is carried out for 30–120 min, and then drying (drying at 60–105 °C for 2–4 h) is carried out to achieve uniform loading of the functional material. When the sol-gel in-situ synthesis loading method (applicable to metal oxides) is selected, metal salts (such as Fe(NO3)3, Al(NO3)3) are used as precursors, and an appropriate amount of complexing agent (such as citric acid) and basic reagent (such as ammonia water) are added to the mixed system. Stirring is carried out for 30–120 min at room temperature to 60 °C to form a sol, and then heat treatment is carried out to form a gel coating, further realizing in-situ loading. During the process, the gradient expansion agent decomposes and releases gases (such as CO2, NH3) at different temperatures in sequence, generating a rich pore structure inside; at the same time, the redox initiator triggers a strong exothermic reaction through microwave radiation, significantly promoting the simultaneous carbonization, cracking and humic acid generation of the components of agricultural and forestry solid wastes, prompting the system to expand rapidly, and forming a developed pore structure with a porosity of 50–90%, including a multi-level pore network of micropores (<2 nm), mesopores (2–50 nm) and macropores (>50 nm).

[0034] Step S32, intelligent post-treatment and functionalization, breaking the reaction product obtained in step S31 into uniform particles; placing the broken particles in a high-speed fluidized mixer or a rotary coater, and spraying and coating an aqueous solution or suspension containing chelated trace elements to obtain a porous slow-release humic acid water-soluble fertilizer.

[0035] The reaction product obtained in step S31 is crushed into particles of 2-5 mm in size by a roller crusher or a jaw crusher, and then further crushed into particles of 50-200 mesh by a hammer crusher or a high-speed impact crusher, and finally finely processed into uniform particles of 200-800 mesh by an ultra-fine airflow crusher; during the crushing process, an online near infrared spectroscopy (NIR) or Raman spectroscopy system is used to monitor the humic acid content (detection accuracy ±1.5%), porosity (detection accuracy ±3%) and heavy metal residue (detection sensitivity ≤0.1ppm) in the particles in real time; then the crushed particles are placed in a high-speed fluidized mixer or a rotary coating machine, and spray-coated with an aqueous solution or suspension containing chelated trace elements, wherein the chelated trace elements are selected from EDTA, citric acid or humic acid complexes of Fe, Zn, Mo, Se, and Cu. The invention discloses a porous slow-release humic acid water-soluble fertilizer, wherein the total amount is 0.05-2%, the concentration of the aqueous solution or suspension containing the chelated trace elements is 0.1-3wt%, the concentration of the aqueous solution or suspension containing the chelated trace elements is 0.01-0.5%, the diameter of the spray droplets is 10-100 μm, and the spraying is continued for 20-60 min at 20-50°C. The microwave power is controlled by infrared temperature measurement feedback so that the reaction temperature fluctuation does not exceed ±10°C. The prepared porous slow-release humic acid water-soluble fertilizer has a responsive release function, that is, when the temperature (25-40°C), pH value (4-8) or humidity (30-90%) environment changes, the internal pore structure of the particles and the coated chelated trace element complex can respond to slight changes in environmental factors, realize physical expansion, pore opening and closing or complex bond breaking, thereby accurately adjusting and controlling the release rate of humic acid and trace elements, and the release rate change error is within ±10%.

[0036] The reaction mechanism of the present invention is as follows:

[0037] (1) Mechanism of low-temperature chlorination for heavy metal removal

[0038] The present invention realizes efficient removal of trace to medium amounts of heavy metal ions (such as Pb) in coal gangue through a two-stage chlorination treatment. 2+ 、Cd 2+ Cr 3+ ). Its reaction mechanism can be divided into two coupled stages:

[0039] 1) Pre-activation stage (150–250°C)

[0040] At a relatively low temperature of 150–250°C, a Cl2 / N2 or Cl2 / O2 mixed gas enters the porous gangue structure, where Cl2 can react with adsorbed metals on the gangue surface in the form of carbonates, hydroxides, and complexes, inhibiting the formation of a stable oxidative passivation film (such as PbO·Fe2O3) at high temperatures. This process is conducive to the interface exposure and activation of reaction sites for subsequent deep reactions.

[0041] 2) Deep removal stage (300–500 °C)

[0042] The core reaction in the high-temperature range of 300–500 °C is the gas-solid phase chlorination reduction reaction between heavy metal oxides and chlorine gas:

[0043]

[0044] This reaction is significantly enhanced at >300 °C. The products such as PbCl2 and CdCl2 are volatile chlorides, which rapidly migrate to the outside and escape or are captured by the tail gas treatment system under the drive of heat.

[0045] 3) Synergistic effect of composite chlorinating agent

[0046] The added alkali metal chlorides such as NaCl and KCl can significantly reduce the free energy barrier of the reaction system and lower the activation energy of the chlorination reaction by about 20–30%. Its microscopic effect is as follows: promoting the diffusion of Cl - in the solid phase, enhancing the local chlorine potential; providing a fluxing phase (eutectic point is about 700 °C), locally forming a quasi-liquid layer, which is beneficial to the migration of metal ions and the improvement of reaction activity.

[0047] Experiments have proved that: compared with the samples without adding the composite chlorinating agent, the usage amount of Cl2 is reduced by about 25%, while the residual concentrations of Pb, Cd, and Cr are reduced by more than 90%.

[0048] (2) Humification and porous structure formation mechanism

[0049] The present invention realizes the integrated construction of humic acid generation and porous structure by constructing a triple-coupled system of redox-gradient expansion-nano loading.

[0050] 1) Redox-triggered chain reaction

[0051] Sodium nitrate (NaNO3) and glucose form a strong oxidation-weak reduction system. After microwave ignition at 180–200 °C, a rapid exothermic oxidative cracking reaction occurs, generating free radicals and small molecule intermediates (CO, CO2, aldehydes and ketones), and triggering the thermal cracking of agricultural and forestry solid wastes (cellulose, lignin) under low-temperature conditions:

[0052] Cellulose → sugar fragments → furfural → aromatic intermediates;

[0053] Lignin → cleavage of phenylpropane skeleton → aryl quinones, phenols → coupling condensation to form humic acid;

[0054] The heat released by the chain reaction can raise the local temperature to 500 °C, forming stable humic acid-like macromolecules (rich in carboxyl groups, hydroxyl groups, and aromatic rings) with low overall energy consumption.

[0055] 2) Gradient foaming-induced porous structure

[0056] By gradually releasing foaming agent gases (CO2, NH3) at different temperatures, a bottom-up multi-scale pore structure is constructed: ammonium bicarbonate decomposes at 120–180 °C, releasing NH3 + CO2 to form microporous channels;

[0057] Urea: The decomposition temperature is 300–350 °C, with a large amount of gas released, expanding to form mesopores;

[0058] Gas diffusion + solidifying wall effect → pore shaping is achieved; the porosity can reach 50–90%, and the measured BET specific surface area increases by 300–500%. Pore size distribution analysis (BJH method) confirms a typical multi-stage distribution: micropores (1–2 nm), mesopores (5–20 nm), and macropores (>50 nm).

[0059] 3) Functional loading mechanism

[0060] In-situ loaded nano-clay, biochar, or metal oxide materials are embedded or bonded through the following mechanisms: clay platelets are adsorbed on humic acid functional group sites (–COOH, –OH) through ion exchange; biochar is embedded in the porous structure of the carbon skeleton to enhance strength; metal oxides (such as Fe3O4) can be formed in-situ under free radical conditions and co-bonded with humic nuclear polymers through π-π interactions.

[0061] (3) Intelligent functional regulation mechanism

[0062] To achieve full-process dynamic quality control, the present invention designs a real-time monitoring and feedback optimization system based on near-infrared (NIR) + AI modeling, which has the following mechanisms:

[0063] 1) Multi-feature fusion analysis

[0064] Based on the system improved from patent CN115063659B, it integrates: NIR near-infrared principal component analysis (PCA) to identify the characteristic absorption bands of humic acid (such as 1450, 1720 cm -1 ); Raman peak positions (such as the C=C bond at 1590 cm -1 , and the C–H bending at 1350 cm -1 ) to analyze the degree of carbonization and structural stability; a multi-level pore light transmittance model to estimate the porosity. The system collects data every 20–30 seconds, and through CNN + multi-variable regression modeling, trains and predicts the changing trends of humic acid content and pore size.

[0065] 2) Feedback optimization control logic

[0066] When the deviation between the collected value and the set target value exceeds the tolerance range (e.g., humic acid is lower than 26%, porosity is lower than 70%), the system starts: dynamic adjustment of microwave power (±10% range); adjustment of the dosing ratio of the gradient bulking agent (e.g., citric acid / ammonium carbonate from 1:2 → 1:3); adjustment of the atmosphere flow rate (CO2 concentration changes by 5–15%); adjustment of the spraying rate (from 1.0 → 1.5 mL / min).

[0067] The results show that: under the AI-assisted feedback, the standard deviation of the humic acid content in the final product is controlled within ±1.3%, the porosity error is within ±2.5%, and the heavy metal residue is stably lower than 0.1 ppm.

[0068] Compared with the prior art, the present invention has the following outstanding features and advantages:

[0069] (1) High-efficiency detoxification and resource recovery

[0070] The present invention adopts a low-temperature segmented chlorination technology, controlling the chlorination temperature at 300–500 °C, significantly lower than the traditional high-temperature heat treatment process at 900–1100 °C. The basis for the energy consumption reduction is as follows: based on the heat required to raise the temperature by 1 °C, estimated according to the specific heat capacity of 1.0 kJ / (kg·K), the traditional process needs to raise the temperature to 1000 °C, while the highest temperature in the present invention is 500 °C, and the unit energy consumption is halved. Coupled with the reduction of the heat preservation time to 1–4 h, the overall heat treatment energy consumption is reduced by about 60%. In addition, the heavy metal removal rate ≥99.5%, which is better than conventional heat treatment or pickling (typical values are 70–85%), because: chlorine is more likely to react with heavy metal ions in the active sites (such as hydroxyl groups and carboxyl groups) on the surface of the coal gangue pores at medium temperature to form volatile chlorides (such as PbCl2, CdCl2), whose boiling points are 953 °C and 960 °C, but can volatilize in advance at 400–500 °C under the action of Cl2, accelerating the reaction kinetics and avoiding the inhibition of the reaction by crystal reconstruction;

[0071] The contents of Pb, Cd, and Cr in the samples treated by the present invention determined by ICP-MS are respectively lower than 0.05 ppm, 0.02 ppm, and 0.01 ppm, far better than the unchlorinated samples (16.4, 7.1, and 3.2 ppm respectively).

[0072] In terms of tail gas treatment, chlorine enters the NaOH absorption tower through the circulation pipeline to generate NaClO / NaCl, and the measured recovery rate reaches 95.3%. Cl2 is converted into hypochlorite under alkaline conditions, with high reaction activity and heat release, and can be instantaneously dissolved and stabilized in the liquid phase system; online Cl2 concentration monitoring (import and export) of the tail gas combined with flow integration shows that ≥95% of Cl2 is collected;

[0073] The design of gradient water washing enables the residual Cl -It drops from the initial 3000 ppm to ≤0.1%, where the pH = 2–9 stepwise water washing + ion exchange combined technology can achieve gradient migration and dynamic equilibrium adsorption; ion chromatography is used to monitor the Cl - concentration after water washing, and the Cl - concentration in the final extract is 0.09 ppm, meeting the agricultural and building materials environmental standards.

[0074] (2) Co - design of functionalized structures

[0075] In the present invention, through the combined reaction of low - temperature induced carbonization + expansion foaming, the product simultaneously generates a humic acid skeleton and a porous structure. Compared with the traditional single carbonization treatment, the humic acid yield is increased by 30% (determined by the HCl extraction method, from 21.3% to 27.6%). The porosity is increased from the original about 60% to 85% (measured by the BET method for specific surface area). The improvement mechanism is as follows: The gradient blowing agent combination (in the order of low - temperature → high - temperature foaming) makes the structure foaming progress layer by layer, avoiding the structure collapse caused by the one - time rapid gas release; while the aromatic structure in humic acid forms a stable carbon skeleton, promoting the reduction of the structure closed - pore rate;

[0076] The product cross - section shows uniformly distributed micropores (<2 nm), mesopores (5–20 nm) and a small number of macropores (>50 nm). Image analysis shows that the multi - level pore structure has good connectivity;

[0077] Lignin / cellulose undergoes oxidative cleavage under the action of an oxidant, forming C = O bonds, and further generating humic polymers through condensation reactions.

[0078] In addition, the in - situ loading of nano - clay and bio - char improves the structural stability and functional properties of the composite material:

[0079] The layered structure of clay (such as montmorillonite) is embedded in the carbon skeleton during the reaction, forming a "scaffold" - type composite structure, relieving pyrolysis shrinkage and enhancing the compressive strength of the material; the measured compressive strength is increased from 0.6 MPa to 0.9 MPa (+50%); the service life is evaluated through the humic acid dissolution experiment, extended from 20 days to more than 60 days (+3 times), indicating that the structural retention ability is significantly enhanced under slow - release conditions.

[0080] (3) Strong adaptability to intelligent and industrialization

[0081] In the traditional resource utilization process of coal gangue, the parameter adjustment is lagged and the control is rough. The present invention introduces a near - infrared spectroscopy (NIR)+AI dynamic regulation system to real - time detect the humic acid content, porosity and impurity level, with errors of ±1.5%, ±3% and ≤0.1 ppm respectively.

[0082] Intelligent regulation mechanism: The system adopts a dual-band NIR signal + Raman excitation feedback module, collects spectra every 30 seconds, analyzes target parameters through a convolutional neural network model (CNN), and realizes closed-loop control of reaction temperature, atmosphere flow rate, and spraying rate;

[0083] Modular microwave-fluidized device design is suitable for large-scale continuous operation:

[0084] Single-module processing capacity: 50–100 kg per batch, and the operating energy consumption does not exceed 150 kWh per ton of materials;

[0085] Cost calculation: Taking tons of materials as the unit, conduct a comprehensive cost accounting of energy consumption + chemicals + waste liquid recovery. The process treatment cost of the present invention is 290 yuan / ton, which is about 40% lower than the traditional carbonization + pickling process (480 yuan / ton). Brief Description of the Drawings

[0086] Figure 1 is the process flow diagram of Embodiments 1 to 3 of the present invention;

[0087] Figure 2 Comparison of heavy metal removal rates in Embodiments 1 - 3;

[0088] Figure 3 Nutrient slow-release period curve of Embodiment 1 。 Detailed Description of the Invention

[0089] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings in the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention. The technical solutions of the present invention will be further described below in conjunction with the implementation cases.

[0090] Embodiment 1

[0091] This embodiment provides a preparation method of a low-temperature humified coal gangue-agricultural and forestry solid waste porous slow-release humic acid water-soluble fertilizer, including the following steps:

[0092] The gangue is subjected to magnetic separation treatment in a dry permanent magnet drum device with a magnetic field intensity of 0.3 T, and then subjected to cationic reverse flotation under the conditions of pH = 2, temperature of 25 °C, reagent concentration of 0.5 mol / L, and bubble size of 1 mm to obtain the pretreated gangue. The flotation time is 20 min, and dodecylamine with an addition concentration of 0.2 mol / L is added as a collector. The flotation product is treated through three crushing processes: after primary crushing by a jaw crusher, it is finely crushed to 50 mesh by a high-speed impact crusher, and then ultrafinely crushed to ≤1 μm by a jet mill. At the same time, nanoscale particles with a particle size of ≤100 nm are separated, and the proportion of nanoscale particles is 5%. The pretreated gangue is obtained.

[0093] Compound chloride A is prepared by mixing MgCl2 and NaCl according to a mass ratio of 1:0.05; the compound chloride A is mixed with the pretreated gangue in a dry mixing method, and the addition amount of the compound chloride A accounts for 10% of the mass of the gangue; the mixing time is 20 minutes, and the mixing uniformity error does not exceed ±2%.

[0094] The Cl2 / N2 / O2 mixed gas is introduced at a rate of 0.5 L / min, and the volume ratio of the three components of Cl2 / N2 / O2 is 30:35:35, and it is heated to 150 °C at a heating rate of 5 °C / min and kept at a constant temperature for 20 min.

[0095] The obtained material is loaded into a closed reaction device, and Cl2 gas with a purity of ≥99% is continuously introduced at a rate of 2 L / min, and the temperature is raised to 300 °C at a rate of 5 °C / min and kept at a constant temperature for 1 hour. The temperature rise is maintained linearly through a heat transfer oil jacket temperature control system, and the reactor is independently temperature-controlled in five sections to keep the temperature difference not exceeding ±10 °C; the tail gas generated by the reaction is circulated and absorbed by an alkali liquor tower, the concentration of NaOH is 1 mol / L, and the cooling stage adopts the inert gas quenching method, and high-purity Ar gas is introduced at a flow rate of 10 L / min to reduce the material temperature to below 40 °C within 30 minutes. The dechlorination process is carried out in three stages of water washing successively, and the water washing is carried out under the conditions of pH = 3, 5.5, 8.5, water washing temperature of 40 °C, stirring time of 30 minutes each, and solid-liquid ratio of 1:3. Finally, through ion exchange treatment, D201 type strong basic anion resin is used, the dosage is 3% of the mass of the material, the exchange time is 1 h, and the dechlorination rate is ≥99.8%. The heavy metal-removed gangue B is obtained.

[0096] Mix gangue B and straw biomass crushed to 10 mesh at a mass ratio of 1:1, place them into a rotary pre-carbonization furnace, and treat at 200 °C for 20 minutes. Subsequently, add a gradient expansion agent: ammonium bicarbonate (decomposition temperature 150 °C) and urea (decomposition temperature 350 °C) are compounded at a mass ratio of 1:1, and the total addition amount is 10% of the mass of the mixture; then add redox initiator NaNO3 and glucose, with a molar ratio of 1:0.2, and the total addition amount of the initiator is 5%. The mixture is placed in a microwave reactor, set the ignition power at 300 W, the reaction temperature is triggered at 180 °C, and react for 10 minutes under a CO2 / N2 atmosphere (volume ratio 1:1, ventilation rate 0.3 L / min). Process monitoring shows that the peak reaction temperature reaches 480 °C, a large amount of CO2 / NH3 gas is released in the system, and a hierarchical pore structure is formed. In-situ add 1% montmorillonite and 1% rice husk carbon with an average particle size of 200 nm to achieve stable loading. The product is processed by three-stage classification and crushing: jaw crusher to 5 mm, hammer mill to 100 mesh, and finally jet mill to 300 mesh.

[0097] Subsequently, place it into a high-speed fluidized bed coating machine, spray an aqueous solution containing 0.05% Fe-EDTA (concentration 1 wt%, droplet size 80 μm), and react for 60 minutes under the conditions of 30 °C, 25% humidity, and pH = 4 to prepare a low-temperature humified gangue-agricultural and forestry solid waste porous slow-release humic acid water-soluble fertilizer.

[0098] The Cl2 recovery rate reaches over 95%. After removal, the obtained material is measured by ICP-MS, and the Pb, Cd, and Cr contents are 0.02 ppm, 0.01 ppm, and 0.05 ppm respectively, and the removal rates are all ≥99.5%.

[0099] 1. Calculation formula for Cl2 recovery rate:

[0100] Testing method:

[0101] Use gas chromatography (GC) to test the amount of recovered Cl2 gas. During the entire removal process, gas is sampled in real time and its concentration is analyzed. The recovery rate is calculated by comparing the concentrations of Cl2 gas before and after removal.

[0102] Instrument: Gas chromatograph (GC), using model 7890B gas chromatograph from Agilent Technologies, equipped with a TCD detector.

[0103] Testing conditions:

[0104] Chromatographic column: HP-5 (30 m × 0.32 mm × 0.25 μm);

[0105] Gas flow rate: 1.0 mL / min;

[0106] Temperature: Column temperature: starting from 40 °C, rising to 250 °C at a rate of 10 °C / min;

[0107] Detector: TCD (thermal conductivity detector), temperature set at 300 °C;

[0108] Detection range: 0.01–1000 ppm.

[0109] Process of obtaining data: By regularly collecting gas samples during the removal process and analyzing their Cl2 concentration, the recovery rate of Cl2 is calculated using the output data of the gas chromatograph.

[0110] 2. ICP-MS test (contents of Pb, Cd, Cr)

[0111] Calculation formula:

[0112] Removal rate:

[0113] Test method:

[0114] Use ICP-MS (inductively coupled plasma mass spectrometry) to test the contents of Pb, Cd, Cr in the removed material.

[0115] Instrument: ICP-MS instrument, using PerkinElmer's Model NexION 300D series, with high sensitivity and high resolution, suitable for the analysis of low-concentration metal elements.

[0116] Test conditions:

[0117] Gas flow rate: The flow rate of Ar (argon) is 0.9 L / min;

[0118] Temperature: The plasma temperature is set at 10,000 K;

[0119] Injection system: Liquid injection, flow rate is 0.1 mL / min;

[0120] Main element standards: Pb, Cd, Cr, calibration concentration range: 0.001–100 ppm.

[0121] Process of obtaining data: By measuring the contents of Pb, Cd, Cr in the sample using ICP-MS, calculating the concentration after removal, and then comparing with the initial concentration to obtain the removal rate.

[0122] Standard sample: Use a standard metal solution as the calibration standard to ensure the accuracy of the test data.

[0123] 3. Determination of porosity and pore size distribution

[0124] Porosity determination formula:

[0125] Porosity:

[0126] Pore size distribution: The porosity and pore size distribution are measured using the BET method (nitrogen adsorption - desorption isotherm method), and the pore volume in different pore size ranges is calculated by combining with the BJH method.

[0127] Instrument: BET surface area and porosity analyzer, using Model 3Flex of Micromeritics, suitable for specific surface area and pore size distribution tests of most materials.

[0128] Test conditions:

[0129] Nitrogen is used as the adsorption gas;

[0130] The test is carried out at low temperature, and the test temperature is 77K;

[0131] The adsorption amount and desorption amount are determined by nitrogen adsorption - desorption isotherm respectively;

[0132] The pore size distribution is calculated by the BJH method (Barrett - Joyner - Halenda method), ranging from micropores to macropores.

[0133] Data derivation process: According to the adsorption - desorption isotherm data, the surface area is calculated using the BET method, and the pore size distribution is analyzed and the porosity is calculated by combining with the BJH method. The results show the proportions of micropores, mesopores and macropores.

[0134] 4. Determination of humic acid content (HCl extraction method)

[0135] Determination formula:

[0136] Porosity:

[0137] Test method:

[0138] The humic acid in the sample is extracted using the HCl extraction method, and then its concentration is determined by ultraviolet - visible spectroscopy (UV - Vis).

[0139] Instrument: Ultraviolet - visible spectrometer, using Model UV - 2600 series spectrometers of Shimadzu.

[0140] Test conditions:

[0141] Injection concentration: 0.1mg / mL humic acid standard solution;

[0142] Measurement wavelength: 340nm;

[0143] Background correction: Use HCl solution as the background solution for calibration.

[0144] Data derivation process: The humic acid concentration was measured at a wavelength of 340 nm by ultraviolet spectroscopy and compared with the standard curve to obtain the content of humic acid in the sample.

[0145] 5. Online near-infrared spectroscopy (NIR) monitoring of changes in humic acid content

[0146] Test method:

[0147] An near-infrared spectroscopy (NIR) instrument was used to monitor the characteristic absorption peak (1720 cm-1) of humic acid in real time. Data was collected every 30 seconds, and the PID microwave control algorithm was combined to automatically adjust the microwave output to maintain the temperature fluctuation ≤ ±10 °C, so as to feedback and optimize the spraying rate and chelating agent concentration.

[0148] Instrument: Near-infrared spectrometer, model Antaris II from Thermo Fisher Scientific, suitable for real-time monitoring of the absorbance of samples.

[0149] Test conditions:

[0150] Spectral range: 1000 - 2500 nm;

[0151] Sampling time: once every 30 seconds;

[0152] Transmission mode: reflection mode, suitable for the analysis of solid samples;

[0153] Accuracy: Temperature control error ≤ ±10 °C, real-time adjustment of spraying rate and chelating agent concentration.

[0154] Data derivation process: The NIR characteristic absorption peak (1720 cm-1) of humic acid was recorded in real time, and the microwave temperature and chelating agent concentration were automatically adjusted through the data feedback PID microwave control system, so as to optimize the reaction process and control the product quality.

[0155] 6. Temperature, pH, humidity-responsive release characteristics

[0156] Test method: The responsive release characteristics of the final product were tested by changing the temperature, pH and humidity. The change in the release rate of the product was measured under different temperature (25–40 °C), pH (4–8) and humidity (30–90%) conditions to ensure that the release rate error ≤ ±10%.

[0157] Equipment: Environmental control box (temperature and humidity adjustable), model Heratherm series from Thermo Fisher Scientific, suitable for adjusting temperature and humidity conditions.

[0158] Test conditions:

[0159] Temperature range: 25–40 °C, tested every 5 °C;

[0160] pH range: 4–8, using different buffer solutions;

[0161] Humidity range: 30–90%, humidity control is achieved through precision constant humidity equipment.

[0162] Data acquisition process: By monitoring the change in release rate under different conditions, calculating the change error of the release rate, ensuring that the error is controlled within ±10%.

[0163] The product porosity was determined to be 82% by nitrogen adsorption - desorption isotherm (BET method). The pore size distribution is as follows: micropores account for 22%, mesopores account for 58%, and macropores account for 20%; the humic acid content is 27.4% (HCl extraction method). The online near - infrared spectroscopy (NIR) instrument collects the characteristic absorption peak of humic acid (1720 cm-1) every 30 seconds, monitors the content change in real - time, combines with the PID microwave regulation algorithm to automatically adjust the microwave output to maintain the temperature fluctuation ≤ ±10 °C, and feedbacks to optimize the spraying rate and chelating agent concentration. The final product has temperature (25–40 °C), pH (4–8), humidity (30–90%) responsive release characteristics, and the change error of the release rate ≤ ±10%.

[0164] Example 2

[0165] This example also provides a preparation method of a low - temperature humified coal gangue - agricultural and forestry solid waste porous slow - release humic acid water - soluble fertilizer, including the following steps:

[0166] Select raw coal gangue, and remove impurities through a combined process of magnetic separation and flotation. The magnetic separation uses a dry permanent magnetic separator with a magnetic field intensity of 0.9 T to remove magnetic iron ore impurities; the flotation conditions are set as pH = 4, adding a collector of dodecylamine with a concentration of 0.2 mol / L, a flotation temperature of 25 °C, controlling the bubble size at 1.5 mm, and the flotation time is 20 min.

[0167] Subsequently, the flotation material is subjected to multi - stage crushing treatment: finely ground to 500 meshes through a high - speed crusher, and then ultra - finely crushed to a particle size ≤ 1 μm through a jet mill, and nanoparticles with a particle size of 10–50 nm are separated, and the content of nanoparticles accounts for about 8%.

[0168] Mix CaCl2 and KCl in a mass ratio of 1:0.2 to prepare a composite chloride agent A, and then dissolve it in deionized water to prepare a 0.5 mol / L impregnation solution.

[0169] Mix the pretreated coal gangue with the composite chloride agent A solution at a liquid - to - solid ratio of 2:1 (mL / g), stir and impregnate at a temperature of 40 °C for 60 min, and after the impregnation is completed, dry it in a hot air oven at 80 °C for 4 hours to complete the loading.

[0170] Load the above impregnated coal gangue materials into the reactor. Adopt a three-stage temperature control structure design, and the interlayer heat-conducting oil circulation system ensures uniform and stable temperature. Pre-activation stage: Introduce a Cl2 / N2 / O2 mixed gas at a rate of 2 L / min. The volume ratio of the three components of Cl2 / N2 / O2 is 30:35:35. The heating rate is 7 °C / min. Heat up to 200 °C and keep it at a constant temperature for 20 minutes to break the inert oxide layer on the metal surface.

[0171] Deep removal stage: Introduce Cl2 gas with a purity ≥ 99%, at a flow rate of 6 L / min. Continue to heat up to 400 °C and keep the reaction for 3 hours to achieve the chlorination and volatilization of heavy metals such as Cd, Pb, and Cr. The tail gas is treated by a NaOH circulating absorption system. The concentration of the NaOH solution is 2 mol / L. Adopt the liquid nitrogen rapid cooling method to quickly reduce the temperature of the reaction product. The liquid nitrogen spraying time is 8 minutes, and the cooling rate is about 40 °C / min. Finally, the temperature of the sample is controlled below 30 °C.

[0172] The water washing stage is carried out in three steps. The pH of the washing liquid is adjusted to 3.0, 5.5, and 8.0 respectively, and the washing time is 30 minutes each. The temperature is controlled at 40 °C, and the solid-liquid ratio is 1:3. The dechlorination treatment adopts the electrodialysis method, with the conditions of voltage 0.8 V / cm, temperature 30 °C, and electrodialysis time 1.5 h. The dechlorination efficiency reaches 99.9%, and the purified coal gangue B is obtained.

[0173] Mix the above coal gangue B with fruit shells and wood chips crushed to 50 mesh. The mass ratio of fruit shells to wood chips is 1:3. The pre-carbonization temperature is 250 °C and the time is 15 minutes. Add a gradient expansion agent system: citric acid (decomposition temperature about 160 °C) and ammonium carbonate (decomposition temperature about 300 °C) are compounded according to a mass ratio of 1:2, and the total addition ratio is 12% of the mass of the composite. The redox initiator is selected as NH4NO3 oxidant and lignosulfonate reductant mixed according to a molar ratio of 1:2, and the total addition ratio is 6%. Put the mixed materials into a microwave reactor and carry out the reaction under the condition of a CO2 / N2 atmosphere (volume ratio 1:3). The microwave ignition power is set to 1000 W, the trigger temperature is 400 °C, and the reaction time is 50 minutes. For the loading of nano-functional materials, add 5% kaolin and 5% bamboo charcoal with a particle size of 100–200 nm. Uniformly distribute and dry them by wet impregnation before mixing. The product is crushed by a roller to a particle size of 3 mm, hammer-crushed to 100 mesh, and air-crushed to 350 mesh. Place it in a rotary coating machine and spray and coat chelated trace elements at 30 °C, pH = 6, and humidity 60%. The chelated trace element solution is a 1% Zn-citric acid complex solution, with a concentration of 2 wt%, the droplet size is about 80 μm, and the spraying time is 45 min to prepare a low-temperature humified coal gangue - agricultural and forestry solid waste porous slow-release humic acid water-soluble fertilizer.

[0174] Referring to the detection means defined in Example 1, the Cl2 absorption rate was determined to be 96.2% by the iodometric method. After treatment by ICP-MS, the contents of Pb, Cd, and Cr in the coal gangue sample were each lower than 0.01 ppm, and the removal rates all exceeded 99.5%. Through BET analysis, the porosity was 87%, and the pore size distribution was mainly mesopores, accounting for about 62%, with micropores and macropores each accounting for 18% and 20% respectively.

[0175] The on-line NIR system was set to sample once every 20 seconds to monitor in real time the changes in the main absorption peak (1450–1720 cm -1 ) of humic acid and the characteristic bands of pore size. If the detected humic acid content deviated by ±1.5%, the microwave holding time or spraying rate was adjusted through the feedback system to automatically maintain the reaction temperature fluctuation within ≤±10 °C. The finally obtained product exhibited significant temperature-humidity-pH responsive release performance, with the release control error within ±8%. Through continuous leaching experiments, it was verified that the release behavior of its Zn element and humic acid presented a three-stage release kinetics of "low-speed start - mid-term steady state - late-stage decline", which was suitable for application in slow-release fertilizers.

[0176] Example 3

[0177] This example also provides a preparation method for a porous slow-release humic acid water-soluble fertilizer from coal gangue - agricultural and forestry solid waste with low-temperature humification, including the following steps:

[0178] The coal gangue was treated by a high-gradient dry magnetic separation device with a magnetic field strength of 1.5 T to fully remove ferromagnetic minerals; then cationic reverse flotation was carried out under the condition of pH = 6, with a flotation temperature of 30 °C, a collector of dodecylamine with a concentration of 0.2 mol / L, a flotation time of 15 min, and the bubble size controlled at 2 mm.

[0179] The obtained flotation concentrate was subjected to multi-stage crushing treatment: the airflow classification mill controlled its particle size to 800 mesh, and was supplemented with an ultrafine crushing device for treatment to ensure that the proportion of particles with a particle size ≤1 μm in the material exceeded 80%, and at the same time contained a nanoscale particle group with a particle size ≤100 nm, accounting for 10%.

[0180] CaCl2 and NaCl were mixed at a mass ratio of 1:0.5 to make a composite chloride A, and formulated into a spray solution with a concentration of 1 mol / L. The coal gangue raw material was maintained in a fluidized bed at 40 °C with an inlet gas velocity of 0.2 m / s to maintain a stable fluidized state, a spraying rate of 1.5 mL / min, the droplet size controlled within the range of 80 μm, and a spraying time of 40 min to ensure the uniform distribution of the chloride on the particle surface.

[0181] Pre-activation stage: A Cl2 / N2 / O2 mixed gas is introduced at a flow rate of 3 L / min, with the volume ratio of Cl2 / N2 / O2 being 50:30:20. The system is heated to 250 °C at a heating rate of 10 °C / min and held at a constant temperature for 30 minutes to promote the conversion of the reaction precursor complex.

[0182] Deep removal stage: Continue to introduce pure Cl2 gas at 8 L / min, heat up to 500 °C, and heat at a constant temperature for 4 hours. The reactor is equipped with five temperature control zones, and a heat transfer oil circulation control system is used to maintain the temperature difference within ±5 °C to ensure that Cl2 reacts fully with metal oxide to form volatile chlorides such as PbCl2 and CdCl2, which are then discharged from the system. The tail gas passes through a NaOH absorption system, with the NaOH solution concentration being 2 mol / L and the gas flow rate being 0.8 L / min. A programmed gradient cooling method is adopted, and it is gradually cooled to room temperature at a rate of 10 °C / min to avoid damage to the pore structure caused by thermal stress.

[0183] Subsequently, three-stage water washing is carried out successively, with water washing under the conditions of pH = 2.5, 5.5, 8.5, temperature 40 °C, and time 30 min each to remove residual inorganic salts. In the dechlorination stage, an ion exchange + electrodialysis combined method is used. First, exchange with 3% D301 strong basic anion resin for 60 min, and then perform electrodialysis treatment at an electric field strength of 0.8 V / cm at 30 °C for 1.5 h. The residual Cl - concentration drops to 0.06% to obtain dechlorinated and purified coal gangue B.

[0184] Mix coal gangue B with agricultural and forestry solid waste (husk: wood chip = 1:1) crushed to 100 mesh in a mass ratio of 1:5, and carry out pre-carbonization treatment at 300 °C for 20 min to enhance the thermal reaction rate and improve the carbon skeleton stability. Add a gradient foaming agent system: citric acid and urea are compounded in a mass ratio of 1:4 (total addition amount 12%) to achieve multi-stage release of CO2 / NH3 to regulate the structure expansion process; at the same time, add a redox initiator: NH4NO3 and glucose are configured in a molar ratio of 1:3, and the addition amount is 5%. The mixture is placed in a microwave reactor and treated under a CO2 / N2 atmosphere (volume ratio 1:5). The microwave ignition power is set to 1500 W, the triggering temperature is 600 °C, and the reaction time is 90 minutes. Humic acid is in-situ generated during the reaction, and the carbon network synchronously expands in structure to form a developed multi-stage pore structure. Add 10% kaolin with a particle size of 200 nm and 10% Fe3O4 precursor (loaded by sol-gel coating method) as in-situ loading functional materials to enhance stability and magnetic responsiveness.

[0185] The product is subjected to three-stage crushing: roll crushing to 2 mm, hammer crushing to 100 mesh, and jet milling to a final particle size of 400 mesh, forming uniformly distributed porous particles. It is placed in a rotary coating machine, and the surface is sprayed with an aqueous solution of EDTA–Fe–humic acid complex, with a total addition amount of 2%, the droplet size is controlled at 50 μm, the spraying temperature is controlled at 40 °C, the humidity is 90%, and the spraying time is 60 min, to prepare a low-temperature humified coal gangue-agricultural and forestry solid waste porous slow-release humic acid water-soluble fertilizer.

[0186] Referring to the detection means of Example 1, the measured Cl2 recovery rate is 96.7%. The heavy metal residues in the coal gangue after treatment (detected by ICP-MS) are lower than 0.05 ppm, and the removal rates of Pb, Cd, and Cr all reach over 99.5%. The product after the reaction is analyzed by BET and shows a porosity of 90%, with micropores accounting for 22% of the porous structure, mesopores accounting for 64%, and macropores accounting for 14%. The system is built-in with an NIR detection module to collect the characteristic absorption peaks of humic acid (1720, 1610 cm -1 ) and the spectral changes related to the pore size, sampling every 30 seconds and automatically identifying the deviation; if the release characteristic simulation deviates by ±10%, the system will feedback the microwave intensity, atmosphere flow rate, and spraying rate through the AI algorithm to achieve automatic adjustment and closed-loop control. The finally prepared porous slow-release humic acid water-soluble fertilizer has excellent response performance, with a stable slow-release rate under the conditions of 40 °C, pH = 8, and humidity of 90%. The chelated iron releases about 34% within 48 hours and reaches the progressive release curve platform within 60 days, which is suitable for alkaline soil improvement and long-term nutrient management scenarios.

[0187] The porous slow-release humic acid water-soluble fertilizers obtained in Examples 1-3 are compared with a commercial humic acid-containing water-soluble fertilizer, a humic acid-containing organic water-soluble fertilizer purchased from Israel's Haipu Chemical Industry Co., Ltd., for the content comparison of national standard parameters, and the test results are shown in Table 1.

[0188] Table 1 Comparison of the technical index performance of humic acid-containing water-soluble fertilizers (large element type) solid products

[0189]

[0190]

[0191] The products obtained from the three examples were all tested with reference to the characterization of NY 1106-2010 "Water-soluble Fertilizer Containing Humic Acid". It can be found that in the three examples, the humic acid content is much higher than the minimum limit of the national standard (≥3.0%) and is 52% - 72% higher than that of commercial products. This is due to the multi-mechanism collaborative design of redox initiation + microwave carbonization + gradient temperature control adopted in the humification process of the present invention, which significantly promotes the thermal cracking and condensation reactions of lignin and cellulose precursors, thereby increasing the humic acid production rate. Example 3 has the highest production efficiency with a content of 38.12% because it uses a high triggering temperature (600°C) and a high proportion of atmosphere regulation (CO2 / N2 = 1:5). The content of macronutrients (total nitrogen, phosphorus, and potassium) in the products of the three examples is significantly higher than the requirements of the national standard and the level of commercial products, indicating that under the control of the humic acid coating and nutrient salt introduction process, the nutrient loading efficiency is good, and there is no significant loss due to the expansion of the porous structure. Example 2 shows the best performance, which may be related to the better uniformity of the raw material carbon skeleton and the spraying coating. The lower the content of insoluble substances (such as unreacted residues and coarse particles), the easier the fertilizer is to dissolve and absorb, and the better the application uniformity. The insoluble substance content of Example 3 is only 0.4%, which is significantly better than 3.8% of commercial products and other examples, indicating that under the conditions of high microwave power and fine particle pretreatment, higher reaction completeness and system uniformity can be achieved. The pH values of all samples are within the specified range, indicating that the fertilizer has good chemical stability. Compared with the slightly acidic property of commercial products, the pH of Example 3 is 5.5, which is in a slightly acidic range more suitable for humic acid adsorption + metal chelation, facilitating the absorption of crop roots and the release of medium and trace elements. Low moisture helps to extend the storage life of the fertilizer, prevent caking, and increase the nutrient content concentration. The moisture content of Example 3 is the lowest, only 0.2%, indicating excellent control of its drying process. It may have adopted efficient means such as liquid nitrogen or programmed temperature reduction combined with vacuum drying, far better than 2.5% of commercial products.

[0192] Examples 1 to 3 systematically demonstrate the comprehensive technical advantages of the present invention in heavy metal removal from coal gangue, humic acid synthesis, porous structure construction, and intelligent slow-release functionalization. Through the multi-mode loading (dry method, wet method, fluidized bed) of magnetic separation - flotation collaborative pretreatment and composite chlorinating agents, combined with segmented temperature-controlled chlorination reactions, the removal rates of heavy metals (Pb, Cd, Cr) are all ≥99.5% and Cl -Excellent purification effect with a residue of ≤ 0.1%. Under different conditions of temperature (180–600 °C), power (300–1500 W), and atmosphere ratio (CO2 / N2 = 1:1–1:5), the microwave-induced humification process can increase the humic acid content to 27.4–38.12%, with a maximum porosity of 90%, effectively regulate the ratio of micropores, mesopores, and macropores, and construct a stable hierarchical pore structure. Example 3 shows the best performance. The overall results indicate that the present invention has a high detoxification rate, high humification efficiency, high structural controllability, and excellent intelligent release performance, significantly superior to existing commercial products and traditional pyrolysis methods.

[0193] Comparative Example 1

[0194] This comparative example provides a method for preparing a porous slow-release humic acid water-soluble fertilizer from coal gangue and agroforestry solid waste by traditional roasting method, which includes the following steps:

[0195] Compared with the preparation method of the low-temperature humification method in Example 2, the traditional roasting method is commonly used for the treatment of coal gangue. By high-temperature roasting, harmful substances in coal gangue are decomposed, and the formation of humic acid is promoted. In the traditional roasting method, first, the same as in Example 2, coal gangue is treated by magnetic separation and flotation processes to remove impurities. The magnetic separation uses a dry permanent magnetic separator with a magnetic field intensity of 0.9 T, and the flotation uses a pH of 4, a collector concentration of 0.2 mol / L of dodecylamine, a flotation temperature of 25 °C, the bubble size is controlled at 1.5 mm, and the flotation time is 20 min. Subsequently, the flotation product is pulverized. First, the coal gangue is pulverized to 500 mesh by a high-speed pulverizer, and then pulverized to a particle size of ≤ 1 μm by a jet mill, and nanoparticles with a particle size of 10–50 nm are separated. Then, the same impregnation treatment method with composite chloride A as in Example 2 is used. CaCl2 and KCl are mixed at a mass ratio of 1:0.2, dissolved in deionized water to prepare a 0.5 mol / L impregnation solution, the liquid-solid ratio is 2:1, stirred at 40 °C for 60 min, and dried at 80 °C for 4 hours after impregnation. The difference is that the traditional roasting method feeds the impregnated coal gangue material into a roasting furnace and conducts roasting at a high temperature of 700 °C for 2 hours to promote the humification reaction. After roasting, Cl2 gas is introduced in the deep dechlorination stage for metal chloride volatilization, with a flow rate of 6 L / min, the temperature is raised to 400 °C and the reaction is maintained for 3 hours, and the tail gas is treated by NaOH circulation absorption. The cooling rate is about 40 °C / min, and the final sample temperature is controlled below 30 °C. The water washing stage is carried out in three steps, respectively regulating the pH of the washing solution to 3.0, 5.5, and 8.0, the temperature is controlled at 40 °C, and the solid-liquid ratio is 1:3; the dechlorination treatment uses electrodialysis with a voltage of 0.8 V / cm and a dechlorination efficiency of 99.9%. The product is treated by coating and chelating trace elements, the particle size of the sprayed coating droplets is about 80 μm, and the spraying time is 45 min. Finally, a porous slow-release humic acid water-soluble fertilizer with low-temperature humification of coal gangue and agroforestry solid waste is prepared. See Figure 2, compared with the microwave reaction method of Example 2, the traditional roasting method requires a higher temperature and a longer reaction time, with greater energy consumption. However, its high-temperature treatment can rapidly decompose harmful substances in coal gangue. Through this comparison, the differences between the traditional roasting method and the low-temperature humification method in terms of energy efficiency, treatment time, and product characteristics can be clearly seen.

[0196] The above-described embodiments merely represent several implementation manners of the present invention, and their descriptions are relatively specific and detailed. However, they should not be construed as limiting the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can be made on their own, and these all fall within the protection scope of the present invention.

Claims

1. A preparation method of a low-temperature humified coal gangue - agricultural and forestry solid waste porous slow-release humic acid water-soluble fertilizer, characterized in that, It includes the following steps: Step S1, low-temperature chlorination of coal gangue to remove heavy metals; Step S2, sectional temperature control and gas regulation; Step S3, low-temperature humification and porous structure construction.

2. The preparation method of the low-temperature humified coal gangue-agricultural and forestry solid waste porous slow-release humic acid water-soluble fertilizer according to claim 1, characterized in that, Step S1 specifically includes the following steps: Step S11, pre-treat the coal gangue by magnetic separation and cationic reverse flotation in sequence; Step S12, prepare composite chloride A by mixing alkaline earth metal chloride and alkali metal chloride; Step S13, mix the composite chloride A prepared in step S12 with the coal gangue pretreated in step S11; the addition amount of the composite chloride A accounts for 5-30% of the mass of the coal gangue.

3. The preparation method of the low-temperature humified coal gangue-agricultural and forestry solid waste porous slow-release humic acid water-soluble fertilizer according to claim 2, characterized in that, Step S11 also includes the operation of crushing the pretreated coal gangue; the mixing method in step S13 is selected from one of dry mixing, wet impregnation mixing and fluidized bed spraying mixing.

4. The preparation method of the low-temperature humified coal gangue-agricultural and forestry solid waste porous slow-release humic acid water-soluble fertilizer according to claim 1, characterized in that, Step S2 specifically includes the following steps: Step S21, pre-activation stage, heat at a certain heating rate to a certain temperature range, and simultaneously introduce a mixed gas of Cl2 and N2 and / or O2; Step S22, deep removal stage, load the material obtained in step S13 into a closed reaction device, control the temperature gradient of the material; continuously introduce chlorine gas with a purity ≥ 99% during the heating process, and recycle and absorb the chlorine-containing tail gas with NaOH solution. The treated material is the heavy metal-removed coal gangue B; Step S23, cooling and post-treatment, cool the heavy metal-removed coal gangue B obtained in step S22 from a high temperature state, and immediately perform multi-stage water washing treatment on the coal gangue B after the cooling step. Finally, perform dechlorination post-treatment on the coal gangue C after water washing to obtain the heavy metal-removed coal gangue D.

5. The preparation method of the low-temperature humified coal gangue-agricultural and forestry solid waste porous slow-release humic acid water-soluble fertilizer according to claim 4, characterized in that, In the mixed gas of Cl2 and N2 and / or O2 in step S21, the proportion of Cl2 is 5-40%, the flow rate of the mixed gas is 0.5-3 L / min, and it is heated at a heating rate of 5-10 °C / min to 150-250 °C for 5-30 min.

6. The preparation method of the low-temperature humified coal gangue-agricultural and forestry solid waste porous slow-release humic acid water-soluble fertilizer according to claim 4, characterized in that, The control of the temperature gradient in step S22 is specifically that the temperature is gradually increased to 300-500 °C at a heating rate of 5-10 °C / min, and is kept at a constant temperature in the target temperature range of 300-500 °C for 1-4 hours.

7. The preparation method of the low-temperature humified coal gangue-agricultural and forestry solid waste porous slow-release humic acid water-soluble fertilizer according to claim 4, characterized in that, The cooling and temperature reduction in step S23 is selected from one of inert gas quenching, liquid nitrogen rapid cooling, and programmed gradient cooling.

8. The preparation method of the low-temperature humified coal gangue-agricultural and forestry solid waste porous slow-release humic acid water-soluble fertilizer according to claim 1, characterized in that, Step S3 specifically includes the following steps: Step S31, mix the heavy metal-removed coal gangue D with agricultural and forestry solid waste, add gradient expanding agent and redox initiator, and trigger the reaction under microwave ignition and CO2 / N2 atmosphere regulation; Step S32, intelligent post-treatment and functionalization, crush the reaction product obtained in step S31 into uniform particles; place the crushed particles in a high-speed fluidized mixer or rotary coater, and spray and coat an aqueous solution or suspension containing chelated trace elements to prepare a porous slow-release humic acid water-soluble fertilizer.

9. The preparation method of the low-temperature humified coal gangue-agricultural and forestry solid waste porous slow-release humic acid water-soluble fertilizer according to claim 8, characterized in that, In step S31, the gradient foaming agent is a compound of a low-temperature foaming agent and a high-temperature foaming agent, with a mass ratio of 1:(1-4); the redox initiator is a combination of a nitrate and a reducing agent, with a molar ratio of nitrate to reducing agent of 1:(0.2-3); the microwave ignition power is 300-1500 W, the triggering temperature is 180-600 °C, and the reaction time is 10-90 minutes.

10. The preparation method of the low-temperature humified coal gangue-agricultural and forestry solid waste porous slow-release humic acid water-soluble fertilizer according to claim 8, characterized in that, The reaction product obtained in step S31 is initially crushed to a particle size of 2-5 mm by a roll crusher or a jaw crusher, further crushed to 50-200 mesh by a hammer mill or a high-speed impact mill, and finally refined into uniform particles with a particle size of 200-800 mesh by an ultrafine air classifier.

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