A method for preparing artificial soil using solid waste

Abstract

This invention discloses a method for preparing artificial soil from solid waste, belonging to the field of solid waste resource utilization technology. The preparation method includes first subjecting mixed solid waste to pre-oxidative pyrolysis and alkali-assisted high-temperature activation, then generating Ca-Mg-Al layered double hydroxide (LDH) in situ under gradient alkaline regulation, followed by granulation with composite nutrients and carbon source and pulsed wet curing to obtain artificial soil with high water stability, low risk of heavy metal migration, and synergistic fast-acting and slow-release fertilization. The artificial soil product of this invention has a TCLP-Pb ≤ 2.8 mg L⁻¹ and a water-stable aggregate content of > 0.25 mm of 80–86%, suitable for mine revegetation, slope greening, and saline-alkali land improvement. The preparation method of this invention fully utilizes the active components of coal-based solid waste and achieves carbon sequestration, improving resource utilization efficiency and ecological benefits.

Description

Technical Field

[0001] This invention relates to the field of solid waste resource utilization technology, specifically to a method for preparing artificial soil using solid waste. Background Technology

[0002] Coal gangue, a major solid waste generated during coal mining and washing, is characterized by low carbon content, low calorific value, and high hardness. Its chemical composition is primarily Al2O3 and SiO2, with varying amounts of Fe2O3, CaO, MgO, Na2O, K2O, P2O5, SO3, and rare elements such as gallium, vanadium, titanium, and cobalt. However, the disposal of coal gangue has become an environmental burden: large-scale stockpiling occupies land resources, and improper management can easily lead to land degradation, salinization, and desertification; the toxic gases produced by spontaneous combustion also constitute an additional source of air pollution. Currently, backfilling and reclamation is the main disposal method for coal gangue (accounting for over 90%), but direct landfilling not only easily causes soil and groundwater pollution but may also induce secondary disasters such as landslides and soil erosion.

[0003] Soil, as a fundamental resource for human survival, is in high demand in areas such as ecological restoration, desertification control, landscaping, and organic agriculture. However, the current ecological problem is characterized by piecemeal solutions. The rise of the artificial soil industry has effectively filled the gap in the soil demand market, protecting land resources and the ecological environment.

[0004] In recent years, coal gangue modification technology has aimed to tap its potential value and transform it into high-value-added environmentally friendly materials. Through techniques such as acid / alkali treatment, mechanochemical treatment, surface organic modification, calcination activation, hydrothermal reaction, and composite modification, the adsorption capacity, reactivity, and material properties of coal gangue have been effectively improved. However, these modification technologies generally suffer from high costs, huge energy consumption, and severe pollution, hindering the resource utilization of coal gangue. Therefore, exploring green, efficient, and low-cost pathways for the resource utilization of coal gangue has become an urgent priority for promoting the sustainable development of the industry.

[0005] It is worth noting that coal gangue originates from the diagenesis of ancient plant-rich humus soils, and its composition is highly similar to that of potting soil, exhibiting soil homology characteristics. Both have similar mineral compositions, mainly consisting of clay minerals and primary minerals. As a coal byproduct, coal gangue is rich in humic acid and various essential trace elements for plants, and is also rich in clay minerals. It has the potential to improve soil moisture retention, enhance carbon sequestration efficiency, and reduce nutrient loss, making it an ideal raw material for developing mineral soil conditioners and potting soils. This also provides new ideas and directions for exploring green, efficient, and low-cost resource utilization pathways for coal gangue.

[0006] In summary, effective solutions must be sought to address the multiple problems caused by coal gangue stockpiling. Summary of the Invention

[0007] The main objective of this invention is to provide a method for preparing artificial soil using solid waste, which can achieve long-term solidification and control of heavy metals, high water stabilization of aggregates and carbon sequestration, while constructing a flexible and scalable resource utilization pathway.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] A method for preparing artificial soil using solid waste includes the following steps:

[0010] (1) Pre-oxidation pyrolysis: Coal gangue and coal gasification slag are mixed and roasted under O2 atmosphere to obtain the roasted product of pre-oxidation pyrolysis;

[0011] (2) Synergistic high-temperature activation: Na2CO3 and CaCl2 are added to the pre-oxidative pyrolysis roasting product for high-temperature activation and calcination. After the calcination is completed, the product is rapidly cooled, pulverized and sieved to obtain activated powder.

[0012] (3) Gradient alkalinity regulation of LDH in situ growth: After adding limestone powder and MgCl2 to the activated powder, the pH of the slurry is adjusted, and after constant temperature stirring reaction, Ca-Mg-Al layered double hydroxide is generated in situ.

[0013] (4) Nutrient-carbon source composite: Ca-Mg-Al layered double hydroxide is mixed with aerobic compost, livestock manure, phosphate rock powder, KCl, trace element fertilizer and biochar to obtain composite material A;

[0014] (5) Multi-strain immobilized granulation: Sodium alginate is sprayed into the rotary drum granulator. When the material-to-water ratio reaches 35-40%, borax is added for cross-linking, and compound microbial agent is sprinkled in at the same time. Granulation continues to obtain wet granules.

[0015] (6) Mixing: Mix composite material A with wet particles to obtain raw material B;

[0016] (7) Pulse wet curing: Raw material B is cured at low temperature to obtain artificial soil.

[0017] By adopting the above method, based on pre-oxidative pyrolysis, synergistic high-temperature activation and LDH in-situ growth, in the "nutrient-carbon source complex" step, harmlessly treated livestock manure can be further incorporated as an auxiliary nitrogen and phosphorus source, which, together with aerobic compost, phosphate rock powder, KCl and trace element fertilizer, can synergistically regulate the rapid and slow release of nutrients; then, through multi-strain immobilization granulation and pulse wet curing, artificial soil suitable for plant growth is obtained.

[0018] Preferably, the raw materials for preparing artificial soil, calculated by weight, include:

[0019] 60-72 parts coal gangue, 28-32 parts coal gasification slag, 1-4 parts Na2CO3, 0.2-1 parts CaCl2, 3-8 parts limestone powder, 1-3 parts MgCl2, 18-32 parts aerobic compost, 5-12 parts livestock manure, 4-10 parts phosphate rock powder, 0.5-1.2 parts KCl, 0.05-0.3 parts trace element fertilizer, 1-5 parts biochar, 0.3-1 part sodium alginate, 0.2-1 part borax, and 0.5-1 part cross-linked composite microbial agent.

[0020] Preferably, in step (1), the particle size of the coal gangue and coal gasification slag is ≤ 10 mm; the roasting is carried out at 420–520 °C and under a 10–20% O2 atmosphere for 0.5–2 h.

[0021] The total sulfur content of the roasted products from pre-oxidative cracking is ≤ 0.3 wt%.

[0022] Preferably, in step (2), the high-temperature activation calcination is carried out at 770–850 °C for 0.5–1 h, followed by rapid cooling to < 200 °C. After rapid cooling, the specific surface area of ​​the activated powder is ≥ 20 m² g. -1 Rapid cooling is achieved using high-pressure steam atomization.

[0023] Preferably, in step (3), the pH of the slurry is adjusted to 6.6–7.2; the constant temperature stirring reaction is carried out at 40–80℃ for 20–60 min; and the specific surface area of ​​the Ca-Mg-Al layered double hydroxide is ≥ 120 m² g. -1 Al 3+ It is produced by the activation and decomposition of coal gangue and coal gasification slag.

[0024] Preferably, in step (4), the aerobic compost has a maturity GI ≥ 80%; the micronutrient fertilizer is ZnSO4·7H2O, H3BO3, (NH4)6Mo7O 24 Mix at a mass ratio of 10:5:1.

[0025] Preferably, the compound microbial agent in step (5) consists of nitrogen-fixing bacteria, phosphate-solubilizing bacteria, and Trichoderma fungi in a mass ratio of 1:1:1; the concentration of viable bacteria in the compound microbial agent is ≥ 1 × 10⁻⁶. 9 CFU g -1 .

[0026] Preferably, the granulation in step (6) is performed by granulating at 20–28 rpm for 10–20 min on a rotary drum granulator; the particle size of the wet particles is 2–9 mm.

[0027] Preferably, the low-temperature curing in step (7) is curing at 28–32 ℃ and 60–85% relative humidity for 10–45 days.

[0028] Preferably, the TCLP-Cd content of the artificial soil is ≤ 0.045 mg / L. -1 .

[0029] The beneficial effects of this invention are as follows:

[0030] 1. The preparation method of this invention first involves pre-oxidative pyrolysis and alkali-assisted high-temperature activation of mixed solid waste, followed by in-situ generation of Ca-Mg-Al layered double hydroxides (LDH) under gradient alkaline regulation. Subsequently, through composite nutrient-carbon source granulation and pulsed wet curing, artificial soil with high water stability, low risk of heavy metal migration, and synergistic fast-acting and slow-release fertilization is obtained. The product has a TCLP-Pb ≤ 2.8 mg / L. -1 With a water-stable aggregate content of 80–86% > 0.25 mm, it is suitable for mine revegetation, slope greening, and saline-alkali land improvement. This invention's process fully utilizes the active components of coal-based solid waste and achieves carbon sequestration, improving resource utilization efficiency and ecological benefits.

[0031] 2. Through a multi-level chemical-mineral-organic synergistic mechanism, the TCLP-Pb, Cd, Cu and other indicators are significantly lower than the standard limits for agricultural sludge.

[0032] 3. The net solid carbon content of the preparation method of the present invention is approximately 0.15 kg CO2 kg. -1 Solid waste management should take into account both ecological restoration and carbon emission reduction. Attached Figure Description

[0033] Figure 1 The artificial soil prepared according to an embodiment of the present invention. Detailed Implementation

[0034] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0035] The following examples use the following raw materials:

[0036] Coal gangue: discharged from a coal preparation plant, with a particle size ≤10 mm after jaw crushing and screening;

[0037] Coal gasification slag: a byproduct of coal gasification units, with a particle size ≤10 mm after magnetic separation to remove iron, and a glass phase content of approximately 68%.

[0038] Na2CO3: Industrial anhydrous purity ≥99%;

[0039] CaCl2: analytical grade;

[0040] Limestone powder: 325 mesh;

[0041] MgCl2 solution: 20% by mass;

[0042] Aerobic composting: Garden waste compost, with a maturity GI ≥ 80%;

[0043] Livestock manure: High-temperature composting, moisture 30%, TN 2.2 wt%, TP 1.3 wt%;

[0044] Phosphate rock powder: P2O5 ≥ 28 wt%, particle size ≤ 100 µm;

[0045] KCl: Agricultural grade potassium chloride, K₂O ≥ 60 wt%;

[0046] Micronutrient fertilizer: ZnSO4·7H2O, H3BO3, (NH4)6Mo7O 24 Mix at a mass ratio of 10:5:1;

[0047] Biochar: Bamboo charcoal, carbonized at 700 °C in an oxygen-deficient environment, specific surface area 250 m² / g -1 ;

[0048] Sodium alginate: viscosity 300 mPa·s (1 wt% solution, 25 °C);

[0049] Borax: Industrial grade;

[0050] Compound microbial inoculant: nitrogen-fixing bacteria, phosphate-solubilizing bacteria, and Trichoderma fungi in a mass ratio of 1:1:1, with a viable count ≥1x10⁻⁶. 9 . Example 1

[0051] 1.1 The raw materials for preparing artificial soil, calculated by weight, include:

[0052] 60 parts coal gangue, 28 parts coal gasification slag, 1 part Na2CO3, 0.2 parts CaCl2, 3 parts limestone powder, 1 part MgCl2, 18 parts aerobic compost, 5 parts livestock manure, 4 parts phosphate rock powder, 0.5 parts KCl, 0.05 parts trace element fertilizer, 1 part biochar, 0.3 parts sodium alginate, 0.2 parts borax, and 0.5 parts compound microbial agent.

[0053] 1.2 Methods for preparing artificial soil:

[0054] (1) Pre-oxidation pyrolysis: Coal gangue and coal gasification slag are mixed and roasted at 420 °C and 10% O2 atmosphere for 0.5 h, and then cooled for later use to obtain roasted product A.

[0055] (2) Synergistic high-temperature activation: Na2CO3 and CaCl2 dry powder were sprayed into the calcined product A, and calcined in a rotary kiln at 770 °C for 0.5 h, followed by steam atomization quenching for ≤10 s; the activated powder was obtained by pulverizing through a 200-mesh sieve, with a specific surface area of ​​23 m². 2 g -1 The high-temperature activated product B was obtained.

[0056] (3) In-situ growth of LDH: The high-temperature activated product B was placed in a shear emulsifier (1200 r / min). -1 In the process of mixing limestone powder with MgCl2 and water, the pH is adjusted to 7.0; then activated powder is added and stirred at 40℃ for 20 min to generate Ca-Mg-Al-LDH.

[0057] (4) Nutrient-carbon source composite: Aerobic compost, livestock manure, phosphate rock powder, KCl, trace element fertilizer and biochar are added sequentially to Ca-Mg-Al-LDH and mixed to obtain composite material C.

[0058] (5) Immobilized granulation: Sodium alginate is sprayed into a rotary drum granulator (24 r / min). -1 When the material-to-water ratio reaches 35%, borax is added for cross-linking, and compound microbial agent is sprinkled in at the same time. Granulation continues for 10 min to obtain 2 mm wet granules.

[0059] (6) The composite material C is mixed with multi-strain immobilized granules to obtain raw material D.

[0060] (7) Pulse wet curing: Raw material D was cured at 28°C and 60% relative humidity for 10 days to obtain artificial soil such as Figure 1 As shown.

[0061] 1.3 Performance indicators of artificial soil:

[0062] CEC of artificial soil 24 cmol kg -1 , TCLP-Pb 2.4 mg L-1, TCLP-Cd 0.043 mg L-1.

[0063] The survival rate of alfalfa planted in artificial soil was 96% after 90 days, with a dry biomass of 6.8 t ha⁻¹.

[0064] Example 2

[0065] 2.1 The raw materials for preparing artificial soil, calculated by weight, include:

[0066] 66 parts coal gangue; 30 parts coal gasification slag; 2.5 parts Na2CO3; 0.6 parts CaCl2; 6 parts limestone powder; 1.5 parts MgCl2; 26 parts aerobic compost; 8 parts livestock manure; 8 parts phosphate rock powder; 0.9 parts KCl; 0.15 parts trace element fertilizer; 3 parts biochar; 0.7 parts sodium alginate; 0.5 parts borax; 0.8 parts compound microbial agent.

[0067] 2.2 Methods for preparing artificial soil:

[0068] (1) Pre-oxidation pyrolysis: Coal gangue and coal gasification slag are mixed and roasted at 460 °C and 15% O2 atmosphere for 1.2 h, and then cooled for later use to obtain roasted product A.

[0069] (2) Synergistic high-temperature activation: Na2CO3 and CaCl2 dry powder were sprayed into the calcined product A, and calcined in a rotary kiln at 800 °C for 0.8 h, followed by steam atomization quenching for ≤10 s; the activated powder was obtained by pulverizing through a 200-mesh sieve, with a specific surface area of ​​23 m². 2 g -1 The high-temperature activated product B was obtained.

[0070] (3) In-situ growth of LDH: The high-temperature activated product B was placed in a shear emulsifier (1200 r / min). -1 In the process of mixing limestone powder with MgCl2 and water, the pH is adjusted to 6.4; then activated powder is added and stirred at 80℃ for 40 min to generate Ca-Mg-Al-LDH.

[0071] (4) Nutrient-carbon source composite: Aerobic compost, livestock manure, phosphate rock powder, KCl, trace element fertilizer and biochar are added sequentially to Ca-Mg-Al-LDH and mixed to obtain composite material C.

[0072] (5) Immobilized granulation: Sodium alginate is sprayed into a rotary drum granulator (24 r / min). -1 When the material-to-water ratio reaches 35%, borax is added for cross-linking, and compound microbial agent is sprinkled in at the same time. Granulation continues for 15 minutes to obtain 5 mm wet granules.

[0073] (6) The composite material C is mixed with multi-strain immobilized granules to obtain raw material D.

[0074] (7) Pulse wet curing: Raw material D is cured for 25 days at 30°C and 70% relative humidity.

[0075] 2.3 Performance indicators of artificial soil:

[0076] CEC23 mol kg of artificial soil-1 TCLP-Pb 2.6 mg L -1 Net solid carbon 0.14 kg CO2 kg -1 .

[0077] Alfalfa planted in artificial soil had a 94% survival rate after 90 days, with a dry biomass equivalent to 6.2 t ha. -1 . Example 3

[0078] 3.1 The raw materials for preparing artificial soil, calculated by weight, include:

[0079] 72 parts coal gangue, 32 parts coal gasification slag, 4 parts Na2CO3, 1 part CaCl2, 8 parts limestone powder, 3 parts MgCl2, 32 parts aerobic compost, 12 parts livestock manure, 10 parts phosphate rock powder, 1.2 parts KCl, 0.3 parts trace element fertilizer, 5 parts biochar, 1 part sodium alginate, 1 part borax, and 1 part compound microbial agent.

[0080] 1.2 Methods for preparing artificial soil:

[0081] (1) Pre-oxidation pyrolysis: Coal gangue and coal gasification slag are mixed and roasted at 520 °C and 20% O2 atmosphere for 2 h, and then cooled for later use to obtain roasted product A.

[0082] (2) Synergistic high-temperature activation: Na2CO3 and CaCl2 dry powders were sprayed into the calcined product A, and calcined in a rotary kiln at 850 °C for 1 h, followed by steam atomization rapid cooling for ≤10 s; the activated powder was obtained by pulverizing through a 200-mesh sieve, with a specific surface area of ​​23 m². 2 g -1 The high-temperature activated product B was obtained.

[0083] (3) In-situ growth of LDH: The high-temperature activated product B was placed in a shear emulsifier (1200 r / min). -1 In the process of mixing limestone powder with MgCl2 and water, the pH is adjusted to 7.2; then activated powder is added and stirred at 60℃ for 60 min to generate Ca-Mg-Al-LDH.

[0084] (4) Nutrient-carbon source composite: Aerobic compost, livestock manure, phosphate rock powder, KCl, trace element fertilizer and biochar are added sequentially to Ca-Mg-Al-LDH and mixed to obtain composite material C.

[0085] (5) Immobilized granulation: Sodium alginate is sprayed into a rotary drum granulator (24 r / min). -1 When the material-to-water ratio reaches 35%, borax is added for cross-linking, and compound microbial agent is sprinkled in at the same time. Granulation continues for 20 minutes to obtain 9mm wet granules.

[0086] (6) The composite material C is mixed with multi-strain immobilized granules to obtain raw material D.

[0087] (7) Pulse wet curing: Raw material D is cured for 45 days at 32°C and 85% relative humidity.

[0088] 3.3 Performance Indicators

[0089] CEC of artificial soil 25 cmol kg -1 TCLP-Pb 2.7 mg L -1 TCLP-Cd 0.041 mg / L -1 24-hour saturated hydraulic conductivity: 1.8 × 10⁻⁶ -5 ms -1 .

[0090] Alfalfa planted in artificial soil had a 95% survival rate after 90 days, with a dry biomass equivalent to 7.1 t ha. -1 .

[0091] The results showed that the artificial soil prepared by this invention had a TCLP-Pb content ≤ 2.8 mg / L. -1 With a water-stable aggregate content of 80–86% > 0.25 mm, it is suitable for mine revegetation, slope greening, and saline-alkali land improvement. This invention's process fully utilizes the active components of coal-based solid waste and achieves carbon sequestration, improving resource utilization efficiency and ecological benefits.

[0092] The specific embodiments of the invention have been described in detail above, but these are merely examples, and the invention is not limited to the specific embodiments described above. For those skilled in the art, any equivalent modifications or substitutions to the invention are also within the scope of this invention. Therefore, all equivalent transformations, modifications, and improvements made without departing from the spirit and principles of this invention should be included within the scope of this invention.

Claims

1. A method for preparing artificial soil using solid waste, characterized in that, Includes the following steps: (1) Mix coal gangue with coal gasification slag and roast it under O2 atmosphere to obtain pre-oxidative cracking roasted product; (2) Add Na2CO3 and CaCl2 to the pre-oxidative pyrolysis roasting product for high-temperature activation and calcination. After calcination, cool rapidly, crush and sieve to obtain activated powder. (3) After adding limestone powder and MgCl2 to the activated powder, the pH of the slurry is adjusted, and after constant temperature stirring reaction, Ca-Mg-Al layered double hydroxide is generated in situ; (4) The Ca-Mg-Al layered double hydroxide was mixed with aerobic compost, livestock manure, phosphate rock powder, KCl, trace element fertilizer and biochar to obtain composite material A; (5) Spray sodium alginate into the rotary drum granulator. When the material-to-water ratio reaches 35-40%, add borax for crosslinking and sprinkle in compound microbial agent. Continue granulation to obtain wet granules. (6) Mix composite material A with wet particles to obtain raw material B; (7) Raw material B is subjected to low-temperature maturation to obtain artificial soil; The raw materials for preparing artificial soil, by weight, include: 60-72 parts coal gangue, 28-32 parts coal gasification slag, 1-4 parts Na2CO3, 0.2-1 parts CaCl2, 3-8 parts limestone powder, 1-3 parts MgCl2, 18-32 parts aerobic compost, 5-12 parts livestock manure, 4-10 parts phosphate rock powder, 0.5-1.2 parts KCl, 0.05-0.3 parts trace element fertilizer, 1-5 parts biochar, 0.3-1 part sodium alginate, 0.2-1 part borax, and 0.5-1 part compound microbial agent; In step (1), the particle size of the coal gangue and coal gasification slag is ≤ 10 mm; the roasting is carried out at 420–520 °C and 10–20% O2 atmosphere for 0.5–2 h. The total sulfur content of the roasting products from pre-oxidative cracking is ≤ 0.3 wt%; In step (2), the high-temperature activation calcination is carried out at 770–850 °C for 0.5–1 h, followed by rapid cooling to < 200 °C. After rapid cooling, the specific surface area of ​​the activated powder is ≥ 20 m² g. -1 Rapid cooling is achieved using high-pressure steam atomization. In step (3), adjust the pH of the slurry to 6.6–7.2; the constant temperature stirring reaction is carried out at 40–80℃ for 20–60 min; the specific surface area of ​​the Ca-Mg-Al layered double hydroxide is ≥ 120 m². 2 g -1 ; In step (7), the low-temperature curing is carried out at 28–32 ℃ and 60–85% relative humidity for 10–45 days.

2. The method for preparing artificial soil from solid waste as described in claim 1, characterized in that, In step (4), the aerobic compost maturity GI is ≥ 80%; the micronutrient fertilizers are ZnSO4·7H2O, H3BO3, and (NH4)6Mo7O. 24 Mix at a mass ratio of 10:5:

1.

3. The method for preparing artificial soil from solid waste as described in claim 1, characterized in that, In step (5), the compound microbial agent consists of nitrogen-fixing bacteria, phosphate-solubilizing bacteria, and Trichoderma fungi in a mass ratio of 1:1:1; the viable bacterial concentration in the compound microbial agent is ≥ 1 × 10⁻⁶. 9 CFU g -1 .

4. The method for preparing artificial soil from solid waste as described in claim 1, characterized in that, In step (5), granulation is performed at 20–28 rpm for 10–20 min on a rotary drum granulator; the wet particle size is 2–9 mm.

5. The method for preparing artificial soil from solid waste as described in claim 1, characterized in that, The TCLP-Cd content in artificial soil is ≤ 0.045 mg / L. -1 .

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