Saline-alkali soil composite modifier based on fine coal gasification slag and preparation method of saline-alkali soil composite modifier

Abstract

The invention discloses a composite modifier for saline-alkali soil remediation and a preparation method thereof. The modifier is prepared from fine coal gasification slag, coke, humic acid and charcoal. The preparation process comprises the following steps: crushing and screening the raw materials, baking biomass to convert the biomass into biochar, mixing according to a ratio, and sequentially performing activation, aging and drying treatment. The core of the invention is to construct a'physical salt resistance-chemical alkali reduction-biological fertility improvement 'triple synergistic remediation system. The hydrophobic coke forms a physical barrier to prevent salt from ascending; the baked and activated biochar and humic acid cooperate to neutralize alkalinity; the coal gasification fine slag is used as a skeleton to improve the soil structure. Pot experiments show that the modifier can significantly reduce the pH value, the conductivity and the total salt content of soil, and in a certain application range, the improvement effect is in positive correlation with the addition amount. The composite modifier is low in raw material cost, environment-friendly, remarkable in synergistic effect of all the components and controllable in effect, and an efficient and synergistic innovative scheme is provided for saline-alkali soil treatment.

Description

Technical Field

[0001] This invention belongs to the interdisciplinary technical field of industrial solid waste resource utilization and saline-alkali land remediation, specifically involving a composite modifier based on coal gasification fine slag and coke, its preparation method, and the application of the modifier in saline-alkali land remediation. Background Technology

[0002] Saline-alkali soils are a type of obstacle soil widely distributed globally. They are characterized by excessive soluble salts and exchangeable sodium, leading to a high soil pH and high sodium content. + Cl - Plasma enrichment leads to increased soil osmotic pressure, inhibiting plant water absorption and causing deterioration of physical and chemical properties. Saline-alkali soils also suffer from problems such as soil compaction, destruction of soil aggregates, low porosity, and poor aeration, which seriously restrict crop growth and ecological environment construction.

[0003] Currently, saline-alkali land improvement technologies are mainly divided into three categories: physical improvement, chemical improvement, and biological improvement. Physical improvement mainly involves methods such as irrigation to leach salt, deep plowing and sun-drying, and soil replacement. This method requires a large amount of water and is prone to raising the groundwater level and causing secondary salinization. Chemical improvement involves applying substances such as gypsum, phosphogypsum, sulfur, and humic acid to replace sodium ions in the soil through ion exchange. However, single chemical amendments have problems such as poor effectiveness, high cost, and potential secondary pollution. Biological improvement mainly involves planting salt-tolerant plants or applying microbial agents, but this method has a long cycle and cannot meet the needs of rapid improvement.

[0004] How to achieve the resource-based and high-value utilization of such industrial solid waste has become an urgent need in the field of environmental protection. Some scholars have used some solid waste and other materials as soil conditioners to improve the soil, but commonly used conditioners may contain certain salts or be alkaline, and their application may introduce new salts or fail to effectively lower the pH. Therefore, developing a new composite conditioner that is low in salt and low in pH, can simultaneously achieve rapid chemical alkali reduction and efficient physical salt control, and uses industrial solid waste as the core raw material, to systematically solve the fundamental problems of saline-alkali land while achieving the goal of "treating waste with waste," has become an important and urgent technical challenge in this field. Summary of the Invention

[0005] To address the shortcomings of existing saline-alkali land improvement technologies, such as limited improvement effects, inability to effectively block salt upwelling, and low utilization rate of industrial solid waste resources, this invention provides a composite soil conditioner using industrial solid waste as the main raw material, along with its preparation method and application. This conditioner not only simultaneously achieves rapid alkali reduction, efficient salt control, and soil structure improvement, but its raw materials also possess excellent physicochemical properties (pH value, electrical conductivity, and total salt content are significantly lower than those of the saline-alkali soil to be remediated). It can chemically dilute soil salinity and neutralize alkalinity, ultimately achieving the goal of "treating waste with waste" and efficiently remediating saline-alkali land.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: A composite soil conditioner based on coal gasification fine slag and its preparation method, comprising the following steps: Firstly, this invention provides a composite soil conditioner for saline-alkali land remediation, composed of the following raw materials: coal gasification slag, coke, humic acid, and biochar.

[0007] Preferably, the composite modifier is composed of the following raw materials in weight percentage: 40-60% coal gasification fine slag, 10-20% coke, 10-25% humic acid, and 15-30% biochar.

[0008] Preferably, the fixed carbon content of the coke is not less than 80%.

[0009] Preferably, the humic acid contains fulvic acid at a content of not less than 70% of the total mass of humic acid.

[0010] Preferably, the heavy metal content in the composite amendment meets the requirements for soil pollution risk screening values ​​for other agricultural land in the "Soil Environmental Quality Standard for Agricultural Land Soil Pollution Risk Control (GB 15618-2018)".

[0011] Preferably, the biochar is plant-derived biochar obtained by baking biomass at 200-350 °C under an inert atmosphere for 30-120 minutes, and the plant-derived biochar is agricultural waste or forestry waste biochar. More preferably, the agricultural waste or forestry waste biochar is one or more of corn stalk biochar, wheat stalk biochar, rice stalk biochar, cotton stalk biochar, oak biochar, and maple biochar.

[0012] Secondly, the present invention provides a method for preparing the above-mentioned composite modifier, comprising the following steps: (1) The coal gasification slag, coke and biomass are crushed separately and passed through a vibrating screen of 0.15-0.3 mm, preferably through a vibrating screen of 0.2-0.3 mm, in order to obtain particles with uniform particle size and increase their specific surface area and reactivity. (2) The crushed and sieved biomass is baked at 200-350 ℃ for 30-120 minutes in an inert atmosphere to obtain biochar. After treatment, it is naturally cooled to room temperature for later use. Biochar obtained by baking biomass transforms it from a relatively inert material into a highly active amendment component. Its surface is rich in acidic oxygen-containing functional groups and loaded with volatile organic acids, and its pH is reduced to a certain extent. This enables it to actively and quickly neutralize soil alkalinity and efficiently fix sodium ions through enhanced ion exchange capacity. At the same time, baking opens up its pore structure and improves its adsorption capacity. After being applied to the soil, it is upgraded from a "physical skeleton" to a "chemical reaction center", achieving rapid alkali reduction, efficient sodium fixation, and synergistic effect with components such as humic acid, which greatly improves the amendment efficiency. (3) Using an electronic balance, accurately weigh the pretreated coal gasification fine slag (40-60%), coke (10-20%), humic acid (10-25%), and biochar (15-30%) according to the above weight percentages; (4) Put the weighed raw materials into a twin-shaft paddle mixer or V-type mixer and mix them at a speed of 20-50 rpm for 10-30 minutes until the components are visually observed to be evenly distributed, forming a basic mixture. (5) Under low-speed stirring, spray pure water slowly and evenly into the basic mixture obtained in step (4) through an atomizing nozzle. Control the spraying speed and water volume so that the final moisture content of the material reaches 15%-25%; this step is the key water activation process, which aims to activate the mixture by stimulating the activity of humic acid through water molecules and triggering the initial colloidal reaction and complexation reaction between materials. (6) Transfer the moistened mixture to a constant temperature and humidity chamber and age it for 2-5 hours at 40-60 ℃ and relative humidity ≥80%. This process can promote the complexation reaction between humic acid and inorganic minerals (fine slag, coke), and enhance the stability and activity of the modifier; (7) Place the aged material in a forced-air drying oven at 80-105 ℃ for drying until the moisture content of the material is less than 10%, preferably reduced to 5%-8%; (8) After drying, mix the material again in a low-speed mixer for a short time (about 5-10 minutes) to homogenize it and ensure batch consistency. Finally, seal the package in a moisture-proof bag and store it in a cool, dry place.

[0013] Thirdly, the present invention provides the application of the above-mentioned composite improver in the remediation of saline-alkali land.

[0014] Preferably, the amount of the composite amendment applied is 5% to 35% of the dry weight of the saline-alkali soil to be remediated. Beneficial effects

[0015] Compared with the prior art, the present invention has the following significant advantages: 1. A new physical mechanism for salt control was invented: by introducing coke components, its inherent hydrophobicity is used to form a capillary barrier layer in the soil, which effectively inhibits the upward movement of salt with water, thus solving the fundamental problem of traditional soil improvement technology that "only washes away salt but does not prevent salt from rising".

[0016] 2. Functionalized and targeted modification of biochar was achieved: Through a low-temperature baking process, biochar was transformed from a traditional physical adsorbent material into a chemically active material rich in acidic functional groups, enabling it to work synergistically with humic acid to achieve rapid and active neutralization of soil alkalinity, breaking through the limitation of weak alkalinity reduction capacity of conventional biochar.

[0017] 3. A multi-waste synergistic remediation system was constructed: fine coal gasification residue (providing framework and minerals), coke (controlling salinity), humic acid (activating and providing functional groups), and functionalized biochar (reducing alkalinity and providing microhabitats) were scientifically compounded to form an integrated synergistic remediation system of "salt control-alkalinity reduction-fertilization", realizing the systematic treatment of salinity and alkalinity obstacle factors.

[0018] 4. Simple and environmentally friendly process: The preparation process does not require complex fermentation or long-term cultivation. The core lies in the precise pretreatment and short-term aging of raw materials, resulting in high production efficiency. The heavy metal content of the product meets national standards, avoiding the risk of secondary pollution and realizing the high-value resource utilization of industrial solid waste. Nationwide, approximately 1.5 billion tons of coal-based solid waste are added annually, of which coal gasification fine slag accounts for approximately 30-50 million tons annually. The investment in environmental protection facilities for treating coal-based solid waste accounts for about one-tenth of the total project investment. Therefore, using industrial solid waste such as coal gasification fine slag as the main raw material for remediating saline-alkali soil achieves high-value utilization of waste and significantly reduces raw material costs.

[0019] 5. Significant effect and dose-response: Pot experiments have shown that the soil conditioner of this invention can significantly reduce soil pH, electrical conductivity and total salt content, enabling plants to grow in saline-alkali soil that would otherwise not grow, and the effect increases with the amount applied. Attached Figure Description

[0020] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 Flowchart of composite modifier preparation.

[0021] Figure 2 Soil physicochemical properties in Examples 1 to 5 Figure 3 Soil leaching toxicity detection structure Detailed Implementation

[0022] The present invention will be further described below with reference to specific embodiments. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Those skilled in the art can make some non-essential improvements and adjustments based on the above-described invention. Example 1

[0023] 1. Preparation of soil conditioner (1) The coal gasification slag, coke and corn stalk biomass are crushed separately and passed through a 0.15mm vibrating screen to ensure uniform mixing with other materials; (2) The crushed and screened corn stalk biomass was baked in an inert atmosphere at 350 °C for 120 minutes to obtain corn stalk biochar. The pretreated corn stalk biochar was naturally cooled to room temperature for later use. (3) Use an electronic balance to accurately weigh 50 kg of pretreated coal gasification fine slag, 20 kg of coke, 10 kg of humic acid and 20 kg of corn straw biochar according to the weight percentage; (4) Put the weighed raw materials into a twin-shaft paddle mixer and mix at 50 rpm for 30 minutes to form a basic mixture with relatively uniform components; (5) Under low-speed stirring, pure water is slowly and evenly sprayed into the basic mixture obtained in step (4) through an atomizing nozzle. The spraying speed and water volume are controlled so that the final water content of the material reaches 25%. The water molecules activate the activity of humic acid and trigger the initial colloidal reaction and complexation reaction between the materials, thereby activating the mixture. (6) Transfer the moistened mixture to a constant temperature and humidity chamber and age it for 5 hours at 60 ℃ and 90% relative humidity. This process can promote the complexation reaction between humic acid and inorganic minerals (fine slag, coke), and enhance the stability and activity of the modifier; (7) Place the aged mixture in a 105 ℃ forced-air drying oven for drying until the moisture content of the material is 5%; (8) After drying, the mixture is mixed again in a low-speed mixer for 10 minutes to homogenize it and ensure batch consistency. Finally, it is sealed in a moisture-proof bag and stored in a cool, dry place.

[0024] 2. Potted plant experiment The amendment prepared above was used. The tested soil was saline-alkali soil, with the following basic physicochemical properties: initial pH value of 8.78, electrical conductivity value of 13.5 dS / m, and total salt content of 0.8%.

[0025] The pot experiment set up a blank group CK (blank saline-alkali soil without any amendment) and a control group T1 (with 10% (by dry weight of soil) of the amendment prepared above).

[0026] Each pot experiment was repeated three times, with the same number of corn kernels planted, light and water conditions, and a cultivation period of 35 days. Soil leaching toxicity was also tested. Example 2

[0027] The soil conditioner prepared in Example 1 above was used. The tested soil was saline-alkali soil with the following basic physicochemical properties: initial pH value of 8.78, electrical conductivity value of 13.5 dS / m, and total salt content of 0.8%.

[0028] The pot experiment set up a blank group CK (blank saline-alkali soil without any amendment) and a control group T2 (with 20% (by dry weight of soil) of the amendment prepared above).

[0029] Each pot experiment was repeated three times, with the same number of corn kernels planted, light and water conditions, and a cultivation period of 35 days. Soil leaching toxicity was also tested. Example 3

[0030] The soil conditioner prepared in Example 1 was used. The tested soil was saline-alkali soil with the following basic physicochemical properties: initial pH value of 8.78, electrical conductivity value of 13.5 dS / m, and total salt content of 0.8%.

[0031] The pot experiment set up a blank group CK (blank saline-alkali soil without any amendment) and a control group T3 (with 30% (by dry weight of soil) of the amendment prepared above).

[0032] Each pot experiment was repeated three times, with the same number of corn kernels planted, light and water conditions, and a cultivation period of 35 days. Soil leaching toxicity was also tested. Example 4

[0033] The modifier was prepared using the same method as in Example 1, except that the composition of the composite agent was changed to 50 kg of coal gasification fine slag, 10 kg of coke, 10 kg of humic acid, and 20 kg of corn straw biochar.

[0034] The tested soil was saline-alkali soil, with the following basic physicochemical properties: initial pH value of 8.78, electrical conductivity value of 13.5 dS / m, and total salt content of 0.8%.

[0035] The pot experiment set up a blank group CK (blank saline-alkali soil without any amendment) and a control group T4 (with 30% (by dry weight of soil) of the amendment prepared above).

[0036] Each pot experiment was repeated three times, with the same number of corn kernels planted, light and water conditions, and a cultivation period of 35 days. Soil leaching toxicity was also tested. Example 5

[0037] The modifier was prepared using the same method as in Example 1, except that the composition of the composite agent was changed to 50 kg of coal gasification fine slag, 15 kg of coke, 10 kg of humic acid, and 20 kg of corn straw biochar.

[0038] The tested soil was saline-alkali soil, with the following basic physicochemical properties: initial pH value of 8.78, electrical conductivity value of 13.5 dS / m, and total salt content of 0.8%.

[0039] The pot experiment set up a blank group CK (blank saline-alkali soil without any amendment) and a control group T5 (with 30% (by dry weight of soil) of the amendment prepared above).

[0040] Each pot experiment was repeated three times, with the same number of corn kernels planted, light and water conditions, and a cultivation period of 35 days. Soil leaching toxicity was also tested.

[0041] Figure 2 The soil physicochemical properties in Examples 1 to 5 clearly demonstrate that this composite soil conditioner has a significant dose-dependent improvement effect on saline-alkali soils. As the proportion of the conditioner increased from 0% (CK) to 30% (T3), the soil pH decreased from 8.78 to 8.19, the electrical conductivity decreased from 13.5 dS / m to 9.09 dS / m (a decrease of 32.7%), and the total salt content decreased from 0.85% to 0.56% (a decrease of 34.1%), proving that within a certain range, the dosage of the conditioner is positively correlated with the improvement effect. Comparing the T3, T4, and T5 groups with different coke contents and the same proportion of composite conditioner, it can be found that with increasing coke content, the pH, electrical conductivity, and total salt content all show a decreasing trend. The above data well reflects the characteristics of this composite soil conditioner: it constructs a triple synergistic remediation system of "physical salt inhibition - chemical alkali reduction - biological fertilization", uses coal gasification fine slag as the skeleton to improve the structure, utilizes the hydrophobicity of coke to block the upward movement of salt, and combines the roasted and activated biochar with humic acid to quickly neutralize alkalinity, which effectively solves the existing problems of saline-alkali soil.

[0042] Figure 3 For soil leaching toxicity testing, the test report shows that the content of all heavy metals in this product is lower than the standard limit, indicating low environmental risk and safe and reliable use.

Claims

1. A composite soil conditioner for saline-alkali land remediation, characterized in that, It is composed of the following raw materials: coal gasification slag, coke, humic acid, and biochar.

2. The composite modifier according to claim 1, characterized in that, The raw materials are composed of the following weight percentages: 40-60% coal gasification slag, 10-20% coke, 10-25% humic acid, and 15-30% biochar.

3. The composite modifier according to claim 1, characterized in that, The fixed carbon content of the coke is not less than 80%.

4. The composite modifier according to claim 1, characterized in that, The humic acid contains fulvic acid at a content of not less than 70% of the total mass of humic acid.

5. The composite modifier according to claim 1, characterized in that, The heavy metal content in the composite amendment meets the requirements for soil pollution risk screening values ​​for other agricultural land in the "Soil Environmental Quality Standard for Agricultural Land Soil Pollution Risk Control (GB 15618-2018)".

6. The composite modifier according to claim 1, characterized in that, The biochar is plant-derived biochar obtained by baking biomass at 200-350°C under an inert atmosphere for 30-120 minutes.

7. The composite modifier according to claim 6, characterized in that, The plant-derived biochar is biochar made from agricultural or forestry waste.

8. The composite modifier according to claim 7, characterized in that, The agricultural or forestry waste biochar is one or more of the following: corn stalk biochar, wheat stalk biochar, rice stalk biochar, cotton stalk biochar, oak biochar, and maple biochar.

9. A method for preparing the composite modifier as described in any one of claims 1 to 8, characterized in that, Includes the following steps: (1) The coal gasification slag, coke and biomass are crushed separately and passed through a vibrating screen of 0.15-0.3 mm, preferably through a vibrating screen of 0.2-0.3 mm, in order to obtain particles with uniform particle size and increase their specific surface area and reactivity. (2) The crushed and sieved biomass is baked in an inert atmosphere at 200-350 °C for 30-120 minutes to obtain biochar. After treatment, it is naturally cooled to room temperature for later use. (3) According to the weight percentages described in claim 2, accurately weigh 40-60% of the pretreated coal gasification fine slag, 10-20% of the coke, 10-25% of the humic acid, and 15-30% of the biochar using an electronic balance; (4) Put the weighed raw materials into a twin-shaft paddle mixer or V-type mixer and mix them at a speed of 20-50 rpm for 10-30 minutes until the components are visually observed to be evenly distributed, forming a basic mixture. (5) Under low-speed stirring, pure water is slowly and evenly sprayed into the basic mixture obtained in step (4) through an atomizing nozzle. The spraying speed and water volume are controlled so that the final water content of the material reaches 15%-25%. This step is the key water activation process, which aims to activate the activity of humic acid through water molecules and trigger the initial colloidal reaction and complexation reaction between materials, thereby realizing the activation of the mixture. (6) Transfer the moist mixture to a constant temperature and humidity chamber and age it for 2-5 hours at 40-60 ℃ and relative humidity ≥80%. This process can promote the complexation reaction between humic acid and inorganic minerals (fine slag, coke) and enhance the stability and activity of the modifier. (7) Place the aged material in a forced-air drying oven at 80-105 ℃ for drying until the moisture content of the material is less than 10%, preferably reduced to 5%-8%; (8) After drying, the material is mixed again in a low-speed mixer for a short time (about 5-10 minutes) to homogenize it, so as to ensure the consistency of product batches. Finally, it is sealed in a moisture-proof packaging bag and stored in a cool and dry place.

10. The application according to claims 1 to 9, characterized in that, The application rate of the composite soil conditioner is 5-35% of the dry weight of the saline-alkali soil to be remediated.

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