Method for preparing artificial soil from solid waste

Abstract

The invention discloses a method for preparing artificial soil from solid waste, and relates to the technical field of solid waste resource utilization, and the preparation method comprises the following steps: carrying out pre-oxidation cracking and alkali-assisted high-temperature activation on mixed solid waste, carrying out gradient alkaline regulation and control to generate Ca-Mg-Al layered double hydroxides (LDH) in situ, and carrying out high-temperature activation on the Ca-Mg-Al layered double hydroxides (LDH); then, through compound nutrient-carbon source granulation and pulse wet solid curing, the artificial soil which is high in aggregate water stability, low in heavy metal migration risk and capable of achieving quick-acting-slow-release synergistic fertilizer supply is obtained. The artificial soil product TCLP-Pb is less than or equal to 2.8 mg L, gt; the content of 0.25 mm water-stable aggregates is 80-86%, and the method is suitable for mine regreening, slope greening and saline-alkali soil improvement; according to the preparation method disclosed by the invention, coal-based solid waste active components are fully utilized, carbon immobilization is realized, and the recycling efficiency and the ecological benefits are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of solid waste resource utilization, and particularly relates to a method for preparing artificial soil by using solid waste. BACKGROUND

[0002] Coal gangue, as the main solid waste generated in the process of coal mining and washing, has the characteristics of low carbon content, low calorific value and high hardness. Its chemical composition is mainly Al2O3 and SiO2, and also contains Fe2O3, CaO, MgO, Na2O, K2O, P2O5, SO3, and rare elements such as gallium, vanadium, titanium and cobalt in varying amounts. However, the disposal of coal gangue has become an environmental burden: large-scale storage occupies land resources, and improper management can lead to land infertility, salinization and desertification; the toxic gases generated by spontaneous combustion also constitute an additional source of air pollution. At present, coal gangue backfilling and reclamation is the main way of disposal (accounting for more than 90%), but direct landfill disposal not only easily causes soil and groundwater pollution, but also may induce secondary disasters such as landslides and soil erosion.

[0003] Soil, as the cornerstone of human survival, has a high demand in the fields of ecological restoration, desertification prevention, landscaping and organic agriculture, but there are ecological problems such as the use of east wall to repair west wall. The rise of artificial soil industry effectively fills the gap in the soil demand market, and protects land resources and the ecological environment.

[0004] In recent years, coal gangue modification technology aims to tap its potential value and convert it into high-value environmental protection materials. Through acid / alkali treatment, mechanical-chemical treatment, surface organic modification, calcination activation, hydrothermal reaction and composite modification, the adsorption capacity, reaction activity and material performance of coal gangue are effectively improved. However, these modification technologies generally have problems such as high cost, high energy consumption and serious pollution, which hinder the process of coal gangue resource utilization. Therefore, exploring green, efficient and low-cost paths for coal gangue resource utilization has become a top priority for promoting the sustainable development of the industry.

[0005] It is worth noting that coal gangue is derived from the rock formation of ancient plant humus-rich soil, and its composition is highly similar to that of nutrient soil, with soil homology characteristics. The mineral composition of both is similar, mainly consisting of clay minerals and primary minerals. As a byproduct of coal, coal gangue is rich in humic acid and various plant essential trace elements, and has a high content of clay minerals, which has the potential to improve soil moisture conservation capacity, enhance carbon sequestration efficiency and reduce nutrient loss. It is an ideal raw material for developing mineral soil conditioners and nutrient soil, which provides a new idea and direction for exploring green, efficient and low-cost paths for coal gangue resource utilization.

[0006] In summary, in order to solve the multiple problems caused by coal gangue storage, effective solutions must be sought. SUMMARY

[0007] The main purpose of the present application is to provide a method for preparing artificial soil from solid waste, which can realize long-term heavy metal control, high water stabilization of granules, and carbon retention, while building a flexible and scalable resource utilization path.

[0008] To achieve the above purpose, the present application provides the following technical solutions: A method for preparing artificial soil from solid waste, comprising the following steps: (1) Pre-oxidation cracking: mix coal gangue and coal gasification slag, and calcine under O2 atmosphere to obtain pre-oxidation cracking calcination products; (2) Synergistic high-temperature activation: add Na2CO3 and CaCl2 to the pre-oxidation cracking calcination products for high-temperature activation calcination, then perform rapid cooling, crushing and sieving to obtain activated powder; (3) Gradient alkaline regulation of in-situ growth of LDH: add limestone powder and MgCl2 to the activated powder, adjust the pH of the slurry, and then generate Ca-Mg-Al layered double hydroxide in-situ after constant temperature stirring reaction; (4) Nutrient-carbon source compound: mix the Ca-Mg-Al layered double hydroxide with aerobic compost, livestock manure, phosphate rock powder, KCl, trace element fertilizer, and biochar to obtain a composite material A; (5) Multi-strain immobilization granulation: spray sodium alginate into a rotary granulator, add borax for crosslinking when the material-water ratio reaches 35-40%, and then continue granulation to obtain wet granules; (6) Mixing: mix the composite material A with the wet granules to obtain a raw material B; (7) Pulse wet solidification: low-temperature curing of the raw material B to obtain artificial soil.

[0009] By using the above method, on the basis of pre-oxidation cracking, synergistic high-temperature activation and in-situ growth of LDH, harmless livestock manure is further added as an auxiliary nitrogen and phosphorus source in the "nutrient-carbon source compound" step, which is used to cooperatively control the release of nutrients with aerobic compost, phosphate rock powder, KCl and trace element fertilizer; and then multi-strain immobilization granulation and pulse wet solidification are performed to prepare artificial soil suitable for plant growth.

[0010] Preferably, the raw materials for preparing artificial soil include, by weight: Coal gangue 60-72 parts, coal gasification slag 28-32 parts, Na2CO3 1-4 parts, CaCl2 0.2-1 part, limestone powder 3-8 parts, MgCl2 1-3 parts, aerobic compost 18-32 parts, livestock manure 5-12 parts, phosphate rock powder 4-10 parts, KCl 0.5-1.2 parts, trace element fertilizer 0.05-0.3 parts, biochar 1-5 parts, sodium alginate 0.3-1 part, borax 0.2-1 part, cross-linked microbial agent 0.5-1 part.

[0011] Preferably, in step (1), the particle size of coal gangue and coal gasification slag is ≤ 10 mm; the calcination is carried out at 420-520 °C under an atmosphere of 10-20% O2 for 0.5-2 h. The total sulfur content of the calcination product of pre-oxidation cracking is ≤ 0.3 wt%.

[0012] Preferably, in step (2), the high-temperature activation calcination is carried out at 770-850 °C for 0.5-1 h, and after the calcination is completed, it is rapidly cooled to < 200 °C; the specific surface area of the activated powder after rapid cooling is ≥ 20 m² g⁻¹; the rapid cooling is carried out by using high-pressure steam atomization cooling.

[0013] 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 °C for 20-60 min; the specific surface area of the Ca-Mg-Al layered double hydroxide is ≥ 120 m² g⁻¹, and the Al 3+ The coal gangue and coal gasification slag are activated and decomposed.

[0014] Preferably, in step (4), the composting degree GI of the aerobic compost is ≥ 80%; the trace element fertilizer is ZnSO4·7H2O, H3BO3, (NH4)6Mo7O 24 Mixed in a mass ratio of 10:5:1.

[0015] Preferably, in step (5), the compound microbial agent is composed of nitrogen-fixing bacteria, phosphorus-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 9 CFU g⁻¹.

[0016] Preferably, in step (6), the granulation is carried out in a rotary drum granulator at 20-28 rpm for 10-20 min; the particle size of the wet granules is 2-9 mm.

[0017] Preferably, in step (7), the low-temperature curing is carried out at 28-32 °C and a relative humidity of 60-85% for 10-45 d.

[0018] Preferably, the TCLP-Cd of the artificial soil is ≤ 0.045 mg L⁻¹.

[0019] The beneficial effects of the present invention are: 1. The preparation method of the present invention first subjects mixed solid waste to pre-oxidative pyrolysis and alkali-assisted high-temperature activation. Then, through gradient alkalinity control, Ca-Mg-Al layered double hydroxides (LDH) are generated in situ. Subsequently, through composite nutrient-carbon source granulation and pulsed wet-solidification, artificial soil is obtained with high water stability, low risk of heavy metal migration, and rapid-release synergistic fertilization. The product has a TCLP-Pb content of ≤2.8 mg L⁻¹ and 80–86% water-stable aggregates > 0.25 mm, making it suitable for mine reforestation, slope greening, and saline-alkali land improvement. This process fully utilizes the active components of coal-based solid waste and achieves carbon sequestration, improving resource utilization efficiency and ecological benefits.

[0020] 2. Through a multi-level chemical-mineral-organic synergistic mechanism, TCLP-Pb, Cd, Cu and other indicators are significantly lower than the standard limits for agricultural sludge.

[0021] 3. The net carbon fixation of the preparation method of the present invention is about 0.15 kg CO2kg -1 Solid waste, taking into account both ecological restoration and carbon emission reduction. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is the artificial soil prepared in the embodiment of the present invention. DETAILED DESCRIPTION

[0023] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0024] The following examples are used in the following raw materials: Coal gangue: discharged from a coal preparation plant, with particle size ≤10 mm after jaw crushing and screening; Coal gasification slag: a by-product of coal gasification equipment, with a particle size of ≤10 mm after magnetic separation and iron removal, and a glassy phase content of approximately 68%; Na2CO3: industrial anhydrous purity ≥99%; CaCl2: analytical grade; Limestone powder: 325 mesh; MgCl2 solution: mass fraction 20%; Aerobic composting: garden waste compost, maturity GI ≥ 80%; Livestock manure: high-temperature composting maturity, moisture 30%, TN 2.2 wt%, TP 1.3 wt%; Phosphate rock: P2O5≥28 wt%, particle size ≤100 µm; KCl: agricultural potassium chloride, K2O≥60 wt%; Trace element fertilizer: ZnSO4·7H2O, H3BO3, (NH4)6Mo7O 24 Mixed in a mass ratio of 10:5:1; Biochar: bamboo charcoal, 700 °C anaerobic carbonization, specific surface area 250 m²g -1 ; Sodium alginate: viscosity 300 mPa·s (1 wt% solution, 25 °C); Borax: industrial grade; Compound microbial agent: azotobacter, phosphorus solubilizing bacteria, Trichoderma sp. in a mass ratio of 1:1:1, viable bacterial count ≥1x10 9 .

[0025] Example 1 1.1 The raw materials for preparing the artificial soil include, by weight fraction: Coal gangue 60 parts, coal gasification slag 28 parts, Na2CO3 1 part, CaCl2 0.2 part, limestone powder 3 parts, MgCl2 1 part, aerobic compost 18 parts, livestock manure 5 parts, phosphate rock 4 parts, KCl 0.5 part, trace element fertilizer 0.05 part, biochar 1 part, sodium alginate 0.3 part, borax 0.2 part, and compound microbial agent 0.5 part.

[0026] 1.2 Method for preparing the artificial soil: (1) Pre-oxidation cracking: mix the coal gangue and coal gasification slag, place in a 420 °C, 10% O2 atmosphere, and calcine for 0.5 h, cool and reserve to obtain calcined product A.

[0027] (2) Synergistic high-temperature activation: spray Na2CO3 and CaCl2 dry powder into the calcined product A, calcine in a 770 °C rotary kiln for 0.5 min, and steam atomize and rapidly cool for ≤10 s; crush to 200 mesh to obtain activated powder with a specific surface area of 23 m 2 g -1 , and obtain high-temperature activated product B.

[0028] (3) In-situ growth of LDH: place the high-temperature activated product B in a shear emulsifier (1200 r min -1 ), mix the limestone powder with MgCl2 and water, and adjust the pH to 7.0; add the activated powder, and stir at 40 °C for 20 min to generate Ca-Mg-Al-LDH.

[0029] (4) Nutrient-carbon source complex: sequentially add aerobic compost, livestock manure, phosphate rock powder, KCl, trace element fertilizer, and biochar into Ca-Mg-Al-LDH to obtain a composite material C.

[0030] (5) Immobilization granulation: spray sodium alginate into a rotary drum granulator (24 r / min -1 ) at a material-to-water ratio of 35%, add borax for crosslinking, and simultaneously sprinkle the composite microbial agent, and continue granulation for 10 min to obtain 2 mm wet granules.

[0031] (6) Mix the composite material C with the multi-strain immobilized granules to obtain raw material D.

[0032] (7) Pulse wet curing: cure the raw material D at 28 °C and a relative humidity of 60% for 10 d to obtain an artificial soil as shown in Figure 1 .

[0033] 1.3 Performance indicators of the artificial soil: The CEC of the artificial soil is 24 cmol / kg -1 , the TCLP-Pb is 2.4 mg / L, and the TCLP-Cd is 0.043 mg / L.

[0034] The survival rate of alfalfa planted in the artificial soil for 90 d is 96%, and the dry biomass is equivalent to 6.8 t / ha.

[0035] Example 2 2.1 The raw materials for preparing the artificial soil include, by weight fraction: Coal gangue 66 parts; coal gasification slag 30 parts; Na2CO3 2.5 parts; CaCl2 0.6 parts; limestone powder 6 parts; MgCl2 1.5 parts; aerobic compost 26 parts; livestock manure 8 parts; phosphate rock powder 8 parts; KCl 0.9 parts; trace element fertilizer 0.15 parts; biochar 3 parts; sodium alginate 0.7 parts; borax 0.5 parts; and composite microbial agent 0.8 parts.

[0036] 2.2 Method for preparing the artificial soil: (1) Pre-oxidation and cracking: mix the coal gangue and the coal gasification slag, place them in a 460 °C furnace in an atmosphere of 15% O2 for 1.2 h, cool, and obtain a calcined product A.

[0037] (2) Synergistic high-temperature activation: spray Na2CO3 and CaCl2 dry powder into the calcined product A, calcine in a rotary kiln at 800 °C for 0.8 min, and steam atomize and rapidly cool for ≤10 s; crush to 200 mesh to obtain an activated powder with a specific surface area of 23 m2 g -1 , obtaining high-temperature activated product B.

[0038] (3) LDH in-situ growth: placing high-temperature activated product B in a shear emulsifier (1200 r min -1 ), mixing limestone powder with MgCl2 and water, adjusting pH to 6.4; adding activated powder to constant temperature stirring at 80°C for 40 min to generate Ca-Mg-Al-LDH.

[0039] (4) Nutrient-carbon source compounding: sequentially adding aerobic compost, livestock manure, phosphate rock powder, KCl, trace element fertilizer, and biochar in Ca-Mg-Al-LDH to obtain composite material C.

[0040] (5) Immobilization granulation: spraying sodium alginate into a rotary drum granulator (24 r min -1 ), adding borax for cross-linking when the material-water ratio reaches 35%, and simultaneously adding composite microbial agent, and continuing granulation for 15 min to obtain 5 mm wet granules.

[0041] (6) Mixing composite material C with multi-strain immobilized granules to obtain raw material D.

[0042] (7) Pulse wet curing: curing raw material D at 30°C and 70% relative humidity for 25 d.

[0043] 2.3 Performance indicators of artificial soil: CEC of artificial soil 23 mol kg -1 , TCLP-Pb 2.6 mg L -1 , net carbon sequestration 0.14 kg CO2 kg⁻¹.

[0044] The survival rate of alfalfa planted in artificial soil for 90 d was 94%, and the dry biomass was equivalent to 6.2 t ha -1 .

[0045] Example 3 3.1 The raw materials for preparing artificial soil include, by weight fraction: coal gangue 72 parts, coal gasification slag 32 parts, Na2CO3 4 parts, CaCl2 1 part, limestone powder 8 parts, MgCl2 3 parts, aerobic compost 32 parts, livestock manure 12 parts, phosphate rock powder 10 parts, KCl 1.2 parts, trace element fertilizer 0.3 parts, biochar 5 parts, sodium alginate 1 part, borax 1 part, and composite microbial agent 1 part.

[0046] 3.2 Method for preparing artificial soil: (1) Pre-oxidation and cracking: coal gangue and coal gasification slag were mixed and placed in a 520 °C, 20% O2 atmosphere for 2 h, and then cooled to obtain a calcined product A.

[0047] (2) Synergistic high-temperature activation: Na2CO3 and CaCl2 dry powder were sprayed into the calcined product A, and calcined in a rotary kiln at 850 °C for 1 min, and then rapidly cooled for ≤10 s by steam atomization; the activated powder was ground to 200 mesh, and the specific surface area was 23 m 2 g -1 , to obtain a high-temperature activated product B.

[0048] (3) In-situ growth of LDH: the high-temperature activated product B was placed in a shear emulsifier (1200 r min -1 ), limestone powder was mixed with MgCl2 and water, and the pH was adjusted to 7.2; the activated powder was added and stirred at 60 °C for 60 min to form Ca-Mg-Al-LDH.

[0049] (4) Nutrient-carbon source complex: aerobic compost, livestock manure, phosphate rock powder, KCl, trace element fertilizer, and biochar were sequentially added to the Ca-Mg-Al-LDH to obtain a composite material C.

[0050] (5) Immobilization and granulation: sodium alginate was sprayed into a rotary granulator (24 r min -1 ), and borax was added for cross-linking when the material-water ratio reached 35%, and a composite microbial agent was also added, and the granulation was continued for 20 min to obtain 9 mm wet granules.

[0051] (6) The composite material C and the multi-strain immobilized granules were mixed together to obtain a raw material D.

[0052] (7) Pulse wet curing: the raw material D was cured at 32 °C and a relative humidity of 85% for 45 d.

[0053] 3.3 Performance indicators The CEC of the artificial soil was 25 cmol kg⁻¹; the TCLP-Pb was 2.7 mg L⁻¹; the TCLP-Cd was 0.041 mg L⁻¹; and the 24 h saturated hydraulic conductivity was 1.8 × 10⁻ 5 m s⁻¹.

[0054] The survival rate of alfalfa planted in the artificial soil for 90 d was 95%, and the dry biomass was equivalent to 7.1 t ha -1 .

[0055] The results show that the artificial soil prepared by the application has TCLP-Pb less than or equal to 2.8 mg L-1, and the water-stable aggregate content of greater than 0.25 mm is 80-86 %, and is suitable for mine greening, slope greening and saline-alkali land improvement. The process fully utilizes the active components of coal-based solid waste and realizes carbon fixation, and improves the resource utilization efficiency and ecological benefits.

[0056] The specific embodiments of the application are described in detail above, but only as examples, and the application is not limited to the specific embodiments described above. Any equivalent modifications or substitutions made by those skilled in the art to the application are also within the scope of the application, and therefore, equivalent transformations, modifications, improvements, etc. made without departing from the spirit and principle range of the application should be covered within the scope of the application.

Claims

1. A method for preparing artificial soil using solid waste, characterized in that: The steps include: (1) Mixing coal gangue and coal gasification slag, and roasting them in an O2 atmosphere to obtain a pre-oxidation cracking roasted product; (2) Na2CO3 and CaCl2 are added to the pre-oxidation cracking calcined product for high-temperature activation calcination. After the calcination is completed, it is rapidly cooled, crushed and sieved to obtain an activated powder; (3) After adding limestone powder and MgCl2 to the activated powder, the pH of the slurry is adjusted, and the Ca-Mg-Al layered double hydroxide is generated in situ after the reaction is stirred at a constant temperature; (4) Mixing Ca-Mg-Al layered double hydroxide with aerobic compost, livestock manure, phosphate rock powder, KCl, trace element fertilizer, and biochar to obtain composite material A; (5) Sodium alginate is sprayed into a rotary drum granulator. When the material-water ratio reaches 35-40%, borax is added for cross-linking. At the same time, a composite bacterial agent is sprinkled in and granulation is continued to obtain wet granules. (6) mixing the composite material A with the wet particles to obtain raw material B; (7) Raw material B is subjected to low-temperature maturation to obtain artificial soil.

2. The method for preparing artificial soil using solid waste according to claim 1, wherein: Calculated by weight, the raw materials for preparing artificial soil include: 60-72 parts of coal gangue, 28-32 parts of coal gasification slag, 1-4 parts of Na2CO3, 0.2-1 parts of CaCl2, 3-8 parts of limestone powder, 1-3 parts of MgCl2, 18-32 parts of aerobic compost, 5-12 parts of livestock manure, 4-10 parts of phosphate rock powder, 0.5-1.2 parts of KCl, 0.05-0.3 parts of trace element fertilizer, 1-5 parts of biochar, 0.3-1 parts of sodium alginate, 0.2-1 parts of borax, and 0.5-1 parts of compound microbial agent.

3. The method for preparing artificial soil using solid waste according to claim 1, wherein: The particle size of the coal gangue and coal gasification slag in step (1) is ≤ 10 mm; the calcination is performed at 420–520 °C and 10–20% O2 atmosphere for 0.5–2 h; The total sulfur content of the calcined product of pre-oxidative cracking is ≤ 0.3 wt%.

4. The method for preparing artificial soil using solid waste according to claim 1, wherein: In step (2), the high temperature activation calcination is carried out by keeping the temperature at 770-850 °C for 0.5-1 h, and then rapidly cooling to < 200 °C after the calcination. The specific surface area of ​​the activated powder after rapid cooling is ≥ 20 m² g⁻¹; the rapid cooling is carried out by high-pressure steam atomization cooling.

5. The method for preparing artificial soil using solid waste according to claim 1, wherein: 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°C for 20–60 min; and the specific surface area of ​​the Ca-Mg-Al layered double hydroxide is ≥ 120 m² g⁻¹.

6. The method for preparing artificial soil using solid waste according to claim 1, wherein: The maturity of aerobic compost in step (4) is GI ≥ 80%; the trace element fertilizer is ZnSO4·7H2O, H3BO3, (NH4)6Mo7O 24 Mix in a mass ratio of 10:5:

1.

7. The method for preparing artificial soil using solid waste according to claim 1, wherein: The composite microbial agent in step (5) comprises nitrogen-fixing bacteria, phosphate-solubilizing bacteria, and Trichoderma fungi in a mass ratio of 1:1:1; the concentration of live bacteria in the composite microbial agent is ≥ 1 × 10 9 CFU g⁻¹.

8. The method for preparing artificial soil using solid waste according to claim 7, wherein: The granulation in step (6) is carried out in a drum granulator at 20–28 rpm for 10–20 min; the particle size of the wet granules is 2–9 mm.

9. The method for preparing artificial soil using solid waste according to claim 1, wherein: In step (7), the low-temperature aging is carried out at 28–32°C and a relative humidity of 60–85% for 10–45 days.

10. The method for preparing artificial soil using solid waste according to claim 9, wherein: TCLP-Cd of artificial soil ≤ 0.045 mg L⁻¹.

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