Method for preparing improved soil through cooperation of petroleum hydrocarbon polluted soil and multi-source solid waste

Abstract

The invention discloses a method for preparing improved soil from petroleum hydrocarbon polluted soil in cooperation with multi-source solid waste, and relates to the technical field of soil remediation and improvement and solid waste treatment. The method comprises the following steps: laying a solid waste material on the top surface of the petroleum hydrocarbon polluted soil, wherein the solid waste material comprises the following components: ceramic blank waste powder, aluminum smelting white slag, phosphogypsum and paper pulp recycled mud; air with the flow speed of V1 is introduced into the petroleum hydrocarbon polluted soil layer, then the bottom of the petroleum hydrocarbon polluted soil layer is preheated, heating is stopped when the temperature of the bottom of the petroleum hydrocarbon polluted soil layer reaches the ignition point of a petroleum hydrocarbon compound, and the flow speed of the air is increased to V2; and when the temperature of the calcining chamber is lower than 300 DEG C, pouring out the calcined product, cooling to room temperature, adding water, and uniformly stirring to obtain the improved soil. Petroleum hydrocarbon pollutants in petroleum hydrocarbon polluted soil can be effectively removed, the activity of solid waste materials can be activated while the petroleum hydrocarbon pollutants are removed, and the compactness and the bearing capacity of the soil can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of soil remediation and improvement and solid waste treatment, and in particular to a method for preparing improved soil by coordinating petroleum hydrocarbon contaminated soil with multi-source solid waste. Background Art

[0002] As some parts of the country adjust their industrial structures and upgrade their industries, a large number of urban industrial parks have been relocated from urban centers. The land left behind by paper mills, metal smelters and coking plants after relocation is usually polluted with organic and inorganic pollution, with major pollutants including petroleum hydrocarbons and heavy metals. These pollutants destroy the composition and structure of the soil, affecting its permeability. In addition, the accumulation of organic pollutants causes them to form difficult-to-decompose residues in the soil, which not only wastes land resources, but also endangers human health and damages the ecological environment.

[0003] At present, the main methods for remediation of organic contaminated soil include solvent extraction, incineration and bioremediation, but the remediation methods generally have problems such as secondary pollution and high treatment costs. The smoldering method is an emerging method for remediation of organic contaminated soil in recent years. The smoldering method uses the high calorific value organic matter in the oil-containing contaminated soil as fuel, and introduces auxiliary air to heat the local area to induce smoldering. Once the smoldering is successfully started, the external heat source can be removed, and the combustion can be spread to other areas by relying on the mass transfer and heat transfer of the gas, thereby achieving the treatment of organic pollutants. It not only reduces operating costs, but also reduces secondary pollution problems. It is an economical, environmentally friendly and sustainable method for treating pollutants. Although the use of the smoldering method to remediate organic contaminated soil can achieve the treatment of organic pollutants in an economical and environmentally friendly way, the heat generated by the combustion of the organic contaminated soil itself in this process is usually directly released to the outside world, making it difficult to fully utilize the heat generated by the combustion of the organic contaminated soil itself. In addition, the repaired soil is relatively loose, has low density, and poor water stability, making it difficult to directly use it in engineering applications such as filling materials and land leveling.

[0004] On the other hand, the disposal of bulk solid wastes such as pulp recycling mud, ceramic embryo waste powder, aluminum slag and phosphogypsum generated by manufacturing industries such as papermaking, ceramics, aluminum processing and phosphate industry faces increasing challenges. Therefore, promoting soil pollution prevention and control and improving the utilization rate of bulk solid waste through the coordinated utilization of industrial solid waste and industrial recycling link technology is a current research hotspot for soil remediation and improvement. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a method for preparing improved soil by combining petroleum hydrocarbon contaminated soil with multi-source solid waste, which can effectively remove petroleum hydrocarbon pollutants in petroleum hydrocarbon contaminated soil and activate the activity of solid waste materials while removing petroleum hydrocarbon pollutants, thereby improving the density and bearing capacity of the soil.

[0006] In order to solve the above technical problems, the present invention provides a method for preparing improved soil by using petroleum hydrocarbon contaminated soil and multi-source solid waste, comprising the following steps:

[0007] (1) laying petroleum hydrocarbon contaminated soil in a calcining chamber, laying solid waste materials on the top surface of the petroleum hydrocarbon contaminated soil, and forming a petroleum hydrocarbon contaminated soil layer and a solid waste material layer in sequence from bottom to top inside the calcining chamber; the components of the solid waste materials include ceramic blank waste powder, aluminum smelting white slag, phosphogypsum and pulp recovery mud;

[0008] (2) introducing air at a flow rate of V1 from the bottom of the petroleum hydrocarbon contaminated soil layer into the petroleum hydrocarbon contaminated soil layer, and then preheating the bottom of the petroleum hydrocarbon contaminated soil layer. When the temperature of the bottom of the petroleum hydrocarbon contaminated soil layer reaches the ignition point of the petroleum hydrocarbon compounds in the petroleum hydrocarbon contaminated soil, the heating is stopped, and the flow rate of the air is adjusted to V2, so that the petroleum hydrocarbon contaminated soil burns from bottom to top; wherein V2 = (1.5-4.5) V1;

[0009] (3) When the temperature of the calcination chamber is lower than 300°C, pour out the calcined product and cool it to room temperature;

[0010] (4) Add water to the cooled calcined product and stir evenly to obtain improved soil.

[0011] Preferably, in step (2), V1 is 1.0-2.0 cm / s; V2 is 3.0-4.5 cm / s.

[0012] Preferably, the content of petroleum hydrocarbon pollutants in the petroleum hydrocarbon contaminated soil is 1500-3500 mg / L.

[0013] Preferably, the components of the solid waste material include 30-35 parts of ceramic embryo waste powder, 20-30 parts of aluminum smelting white slag, 15-20 parts of phosphogypsum and 25-30 parts of pulp recovery mud, calculated by weight.

[0014] In step (1), the amount of solid waste material added is 8% to 14% of the mass of the petroleum hydrocarbon contaminated soil, calculated as a percentage by mass.

[0015] Preferably, calculated by mass percentage, the ceramic blank waste powder comprises the following chemical components: CaO 1-5%, SiO2 60-75%, Al2O3 12-21%, Fe2O3 1-3%, Na2O 1-3%, MgO 1-5%, and LOI 2-5%.

[0016] Preferably, calculated by mass percentage, the aluminum smelting white slag includes the following chemical components: CaO 1-2%, SiO2 2-6%, Al2O3 68-77%, Fe2O3 1-3%, MgO 8-15%, AlN 5-15%, and LOI 0.1-1%.

[0017] Preferably, calculated by mass percentage, the phosphogypsum includes the following chemical components: CaO 35-45%, SiO2 1-3%, Al2O3 0.1-1%, Fe2O3 0.1-1%, SO3 50-60%, F 0.5-1.2%, P2O5 1-3%, LOI 1-5%.

[0018] Preferably, calculated by mass percentage, the recycled pulp mud includes the following chemical components: CaO 57-65%, SiO2 1-4%, Al2O3 1-2%, Fe2O3 5-8%, Na2O 9-17%, Cr2O3 0.2-0.25%, CuO 0.13-0.19%, MgO 1-2%, and LOI 5-14%.

[0019] Preferably, the particle size of the ceramic blank waste powder is ≤75 μm;

[0020] The particle size of the aluminum smelting white slag is ≤75 μm;

[0021] The particle size of the phosphogypsum is ≤75 μm;

[0022] The particle size of the recycled pulp sludge is ≤900 μm.

[0023] Preferably, in step (2), the bottom of the contaminated soil layer is preheated at a temperature of 450 to 550° C. and a preheating time of 1 to 2 hours.

[0024] The implementation of the present invention has the following beneficial effects: the present technical solution uses smoldering as a method for treating petroleum hydrocarbon contaminated soil. By using the high calorific value petroleum hydrocarbons present in the oil-containing contaminated soil as fuel, the local area is heated to induce smoldering under the condition of introducing auxiliary air, and the combustion is allowed to spread to other areas by itself by relying on the mass transfer and heat transfer effect of the gas, thereby achieving the treatment of petroleum hydrocarbon contaminated soil. At the same time, the heat of the combustion of petroleum hydrocarbon contaminated soil is fully utilized to stimulate the activity of solid waste materials, and the solid waste materials are gradually sintered and transformed from loose to dense clinker. After adding water and stirring and mixing, improved soil with dense structure and good water stability can be obtained. The improved soil of the present technical solution can be used in engineering applications such as filling materials and land leveling, which not only solves the problem of soil pollution, but also makes full use of solid waste and alleviates the accumulation and disposal of solid waste. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1It is a schematic structural diagram of a calcining chamber used in the method for preparing improved soil by using petroleum hydrocarbon-contaminated soil and multi-source solid waste in Example 1 of the present invention;

[0026] In the figure: calcination chamber 1, heating chamber 2, petroleum hydrocarbon contaminated soil 3, solid waste material 4, heating equipment 5, air inlet channel 6, blower 7, feed port 11, exhaust port 12, temperature detection device 13. DETAILED DESCRIPTION

[0027] To make the purpose, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings. The present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present invention more thorough and comprehensive.

[0028] If no specific techniques or conditions are specified in the examples, the techniques or conditions described in the literature in the field or the product instructions are used. Raw materials used without specifying the manufacturer are all conventional products that can be obtained through commercial purchase.

[0029] A method for preparing improved soil by using petroleum hydrocarbon contaminated soil and multi-source solid wastes comprises the following steps:

[0030] (1) laying petroleum hydrocarbon contaminated soil in a calcining chamber, laying solid waste materials on the top surface of the petroleum hydrocarbon contaminated soil, and forming a petroleum hydrocarbon contaminated soil layer and a solid waste material layer in sequence from bottom to top inside the calcining chamber; the components of the solid waste materials include ceramic blank waste powder, aluminum smelting white slag, phosphogypsum and pulp recovery mud;

[0031] (2) introducing air at a flow rate of V1 from the bottom of the petroleum hydrocarbon contaminated soil layer into the petroleum hydrocarbon contaminated soil layer, and then preheating the bottom of the petroleum hydrocarbon contaminated soil layer. When the temperature of the bottom of the petroleum hydrocarbon contaminated soil layer reaches the ignition point of the petroleum hydrocarbon compounds in the petroleum hydrocarbon contaminated soil, the heating is stopped, and the flow rate of the air is adjusted to V2, so that the petroleum hydrocarbon contaminated soil burns from bottom to top; wherein V2 = (1.5-4.5) V1, and the units of V1 and V2 are both cm / s;

[0032] (3) When the temperature of the calcination chamber is lower than 300°C, pour out the calcined product and cool it to room temperature;

[0033] (4) Add water to the cooled calcined product and stir evenly to obtain improved soil.

[0034] Specifically, the present technical scheme is a method for preparing improved soil by using petroleum hydrocarbon contaminated soil in combination with multi-source solid wastes. The waste powder of ceramic embryo materials, aluminum slag, phosphogypsum, and pulp recovery mud are mixed into solid waste materials. The petroleum hydrocarbon contaminated soil is used as the bottom layer, and the solid waste materials are laid on top of the petroleum hydrocarbon contaminated soil as the second layer in a calcining chamber. The preheating device of the calcining chamber is started to preheat the bottom of the petroleum hydrocarbon contaminated soil layer. When the temperature reaches the ignition point of the petroleum hydrocarbon compound, the preheating device is turned off. Based on the present technical scheme, air is injected into the petroleum hydrocarbon contaminated soil layer. Petroleum hydrocarbons with higher calorific value are used as energy, causing the petroleum hydrocarbon-contaminated soil to burn slowly and self-sustainingly, and by adjusting the air flow rate, the burning speed and temperature are controlled, so that the petroleum hydrocarbon-contaminated soil can burn continuously from bottom to top; the bottom-up combustion of petroleum hydrocarbons provides a high-temperature calcination environment for the second layer of solid waste materials, stimulates the gelling activity of the solid waste materials, and forms solid waste-based gelling clinker after cooling after calcination; water is added to the petroleum hydrocarbon-contaminated soil-solid waste material mixture (i.e., the calcination product) after calcination and cooling, and the improved soil is prepared after uniform mixing.

[0035] It is worth noting that this technical solution uses high calorific value organic matter (i.e., petroleum hydrocarbons) present in petroleum hydrocarbon contaminated soil as fuel, and introduces auxiliary air to heat a local area (i.e., the bottom of the contaminated soil layer) to induce smoldering, and utilizes the combustion of the petroleum hydrocarbon contaminated soil itself to induce continuous combustion of the surrounding area (the contaminated soil layer and the solid waste material layer). While removing pollutants from the petroleum hydrocarbon contaminated soil, this technical solution can stimulate the activity of the solid waste material under the high-temperature calcination caused by the smoldering, and the solid waste material gradually sintered and transformed from a loose state to a densely structured clinker. After adding water to the calcined product (i.e., a mixture of petroleum hydrocarbon-contaminated soil and solid waste materials) and stirring and mixing, the active substances in the calcined pulp recovery mud react with water to generate alkaline substances, providing an alkaline environment for the active silicon and aluminum phases in the ceramic blank waste powder and aluminum slag, which can promote the formation of cementitious products such as hydrated calcium silicate and hydrated calcium aluminate, cement soil particles, refine the pores of soil particles, and form a skeleton structure. At the same time, the sulfate ions in the phosphogypsum can react with calcium aluminate hydrate in an alkaline environment to generate needle-shaped calcium aluminate, which fills the pores between soil particles, and can further improve the soil density, forming a compact structure and improved soil with good water stability. This technical solution makes full use of large solid wastes such as ceramic blank waste powder, aluminum slag, phosphogypsum and pulp recovery mud, and alleviates the resource and environmental pressures brought about by the accumulation of solid wastes. The solid waste materials of this technical solution are thermally activated by the heat of petroleum hydrocarbon combustion, which can fully utilize the heat generated by the combustion of petroleum hydrocarbon-contaminated soil itself, not only reducing the additional energy consumption required for mechanical grinding and excitation, but also avoiding the negative effects of chemical excitation (such as acid excitation and alkali excitation) that may destroy the acid-base balance of the soil.

[0036] Further explanation, specifically, this technical solution uses smoldering as a method for treating petroleum hydrocarbon contaminated soil. By using the high calorific value petroleum hydrocarbons in the oil-containing contaminated soil as fuel, the local area is heated to induce smoldering under the condition of introducing auxiliary air, and the combustion is allowed to spread to other areas by itself by relying on the mass transfer and heat transfer of the gas, thereby achieving the treatment of petroleum hydrocarbon contaminated soil. At the same time, the combustion heat is fully utilized to stimulate the activity of solid waste materials, and the solid waste materials are gradually sintered, and the loose state is transformed into a dense clinker. After adding water and stirring, the improved soil is made. The improved soil prepared by this technical solution has a dense structure and good water stability. It can be used in engineering applications such as filling materials and land leveling, which not only solves the soil pollution problem, but also makes full use of solid waste and alleviates the accumulation and disposal of solid waste. And compared with traditional treatment technologies, the method for treating petroleum hydrocarbon contaminated soil in this technical solution avoids the problems of large solvent consumption, high treatment cost and possible secondary pollution caused by solvent extraction; avoids the problem of high equipment investment caused by incineration; and avoids the problems of long treatment cycle and low treatment efficiency caused by bioremediation.

[0037] To further explain, aluminum smelting white slag is the waste slag from the production of aluminum profiles. The technical solution adopts the original aluminum smelting white slag that has not been treated by the water washing process. The original aluminum smelting white slag contains aluminum nitride and has a large amount of volatile ammonia. The calcination process can neutralize the sulfur dioxide gas generated by the calcination of phosphogypsum and the carbon dioxide gas generated by the calcination of pulp recovery mud to reduce harmful gas emissions.

[0038] Specifically, the ignition point is the temperature threshold at which a substance burns, and is the lowest temperature point at which a substance can be ignited.

[0039] Preferably, before laying the solid waste material on the top surface of the petroleum hydrocarbon contaminated soil in step (1), the method further includes a step of preparing the solid waste material. The specific method is as follows: pouring the waste powder of ceramic embryo materials, aluminum smelting white slag, phosphogypsum and pulp recovery mud into the uppermost sieve of the automatic vibrating screen machine respectively, covering the sieve cover and placing it on the sieve support of the vibrating screen machine, setting the timer to start the automatic vibrating screen machine after 6 minutes, the vibration amplitude of the vibrating screen machine is 8 mm, the vibration frequency is 147 / min, the sieve shaking frequency is 221 / min, and the rotation radius is 12.5 mm. Take the ceramic blank waste powder, aluminum smelting white slag and phosphogypsum after sieving with a 75μm sieve, and the pulp recovery mud after sieving with a 800-900μm sieve, put them into the agitator for mixing, and set the agitator to stir the mixture of ceramic blank waste powder, aluminum smelting white slag, phosphogypsum and pulp recovery mud at 300rpm for 2min, adjust the speed to 1000rpm and stir for 2min to make solid waste material and set it out for use.

[0040] Preferably, in step (1), petroleum hydrocarbon contaminated soil is placed as the bottom layer in the calcination chamber, and its pile height does not exceed 40 cm, and solid waste materials are placed as the second layer in the calcination chamber, and its pile height does not exceed 20 cm.

[0041] Preferably, the technical solution is provided with thermocouples at 0cm, 20cm, 40cm and 60cm inside the calcining chamber, which are used to detect the temperature data at different heights inside the calcining chamber. In one embodiment of the technical solution, in step (2), when the temperature at 0cm in the calcining chamber reaches 500°C and the temperature at 20cm in the calcining chamber reaches 450°C, the preheating device is turned off to stop heating, and the air flow rate V2 is increased to (1.5-4.5) V1. During this period, the gas generated in the calcining chamber is collected by an external exhaust gas collection system.

[0042] Specifically, after the smoldering starts, the petroleum hydrocarbon-contaminated soil inside the calcination chamber is calcined from bottom to top. During the calcination process, the temperature inside the calcination chamber can reach 900℃~1200℃ at the highest. The calcination process can last for 2~6 hours, providing a high-temperature calcination environment for the solid waste materials and stimulating the gelling activity of the solid waste materials. When the materials in the calcination chamber are fully burned, the inside of the calcination chamber enters the cooling stage, and the temperature of the calcination chamber gradually decreases. When the temperature of the calcination chamber is lower than 300℃, the calcined products in the calcination chamber can be poured out and cooled to room temperature.

[0043] Specifically, in step (4), an appropriate amount of water is added to the cooled calcined product, and the mixture is stirred evenly to obtain improved soil. Preferably, the technical solution refers to the test method for the optimal moisture content in JTG 3441-2024 "Testing Procedure for Stabilized Materials of Inorganic Binders for Highway Engineering", detects the optimal moisture content of the calcined product, and calculates the amount of water added to the calcined product according to the optimal moisture content to prepare improved soil with better strength.

[0044] Further explanation, the technical solution adopts a calcining furnace for smoldering. The calcining furnace adopted in the technical solution is well known and can be used for calcining in the market. Figure 1 The calciner shown is used to calcine petroleum hydrocarbon contaminated soil and solid waste materials, but is not limited to this. Figure 1The calcining furnace shown includes a calcining chamber 1 and a heating chamber 2. The calcining chamber 1 is used to hold petroleum hydrocarbon contaminated soil 3 and solid waste materials 4. A heating device 5 (such as a heating wire or a heating plate, etc.) is provided in the heating chamber 2 to preheat the petroleum hydrocarbon contaminated soil, and an air inlet channel 6 is provided at the bottom of the heating device 5. The air inlet channel 6 is connected to an external blower 7. The air inlet channel 6, the heating chamber 2 and the calcining chamber 1 are connected in sequence to introduce air into the calcining chamber. A feed inlet 11 and an exhaust port 12 are provided at the upper part of the calcining chamber 1, and a discharge port (not shown in the figure) is provided at the bottom of the calcining chamber 1. Temperature detection devices 13 are provided at 0 cm, 20 cm, 40 cm and 60 cm of the calcining chamber 1. The temperature detection device can be a thermocouple.

[0045] To further illustrate, in step (2), V1 is 1.0 to 2.0 cm / s; V2 is 3.0 to 4.5 cm / s.

[0046] It is worth noting that in the preheating stage, the air velocity V1 is maintained at 1.0-2.0 cm / s. The slower velocity is conducive to heat accumulation, so that the heat generated by the preheating accumulates inside the petroleum hydrocarbon contaminated soil layer, and mainly accumulates in the lower part of the petroleum hydrocarbon contaminated soil layer, which is conducive to the initiation of smoldering; the air velocity V1 in the preheating stage should not be too high, otherwise it is easy to cause the heat generated by the combustion of petroleum hydrocarbons to be quickly taken away. After the preheating stage stops, the combustion reaction begins. At this time, the heating is stopped. The contaminated soil relies on the petroleum hydrocarbons with higher calorific value as energy and slowly self-sustains combustion. At this stage, the air velocity is increased to V2 (3.0-4.5 cm / s). Relying on the mass transfer and heat transfer of the gas, the combustion spreads to other areas by itself, so that the petroleum hydrocarbon contaminated soil continues to burn from bottom to top, thereby realizing the treatment of the petroleum hydrocarbon contaminated soil. Moreover, under the action of the higher velocity of air, it is more conducive to stimulating the activity of solid waste materials.

[0047] It is further explained that the content of petroleum hydrocarbon pollutants in the petroleum hydrocarbon contaminated soil is 1500-3500 mg / L.

[0048] It is worth noting that the concentration of petroleum hydrocarbon pollutants in the petroleum hydrocarbon contaminated soil of the present technical solution is 1500-3500 mg / L. Within this range, the concentration of petroleum hydrocarbon pollutants can form an oxidation reaction zone of a certain thickness to trigger smoldering start and make the petroleum hydrocarbon contaminated soil burn from bottom to top. If the concentration of petroleum hydrocarbon pollutants in the petroleum hydrocarbon contaminated soil is too low or too high, it is difficult to form an oxidation reaction zone of a certain thickness, and it is difficult to maintain smoldering start and self-sustaining propulsion.

[0049] Preferably, the type of petroleum hydrocarbon pollutants in the petroleum hydrocarbon contaminated soil of the present technical solution is a type of base oil, which is directly extracted from crude oil processing in a refinery. Its main characteristics are low molecular weight, high aromatic content, high volatility and poor oxidation stability. Therefore, it is mostly used for low-requirement lubricants, such as sawing oil, cutting oil, etc.

[0050] Further explanation, calculated by weight, the components of the solid waste material include 30-35 parts of ceramic embryo waste powder, 20-30 parts of aluminum smelting white slag, 15-20 parts of phosphogypsum and 25-30 parts of pulp recovery mud. Within the limited dosage range, more cementitious products can be generated after calcination, which can better cement soil particles and refine the pores of soil particles, thereby forming improved soil that is conducive to compact structure and good water stability.

[0051] The amount of ceramic blank waste powder added to the solid waste material of the present technical solution is 30 to 35 parts, exemplarily 30 parts, 31 parts, 32 parts, 33 parts, 34 parts, and 35 parts, but not limited thereto. The amount of aluminum slag added in the present technical solution is exemplarily 20, 22 parts, 24 parts, 25 parts, 26 parts, 28 parts, and 30 parts, but not limited thereto. The amount of phosphogypsum added in the present technical solution is exemplarily 15 parts, 16 parts, 17 parts, 18 parts, 19 parts, and 20 parts, but not limited thereto. The amount of pulp recovery mud added in the present technical solution is exemplarily 20, 22 parts, 24 parts, 26 parts, 28 parts, and 30 parts, but not limited thereto.

[0052] Further explanation, calculated by mass percentage, the ceramic blank waste powder includes the following chemical components: CaO 1-5%, SiO2 60-75%, Al2O3 12-21%, Fe2O3 1-3%, Na2O 1-3%, MgO 1-5%, LOI 2-5%.

[0053] Preferably, the ceramic blank waste powder of the technical solution is selected from the waste formed before the ceramic products are fired, the powder residue is fine, and has high volcanic ash activity after calcination at 700℃~800℃. According to the mass percentage, the ceramic blank waste powder of the technical solution mainly includes the following chemical components: CaO 1~5%, SiO2 60~75%, Al2O312~21%, Fe2O3 1~3%, Na2O 1~3%, MgO 1~5%, LOI 2~5%. The main components of the ceramic blank waste powder after calcination - active silicon dioxide and active aluminum oxide components can react with calcium hydroxide to form cementitious products such as hydrated calcium silicate and hydrated calcium aluminate to consolidate soil particles and play the role of pressure-bearing structural skeleton, thereby improving the strength of the soil.

[0054] Further explanation, calculated by mass percentage, the aluminum smelting white slag includes the following chemical components: CaO 1-2%, SiO2 2-6%, Al2O3 68-77%, Fe2O3 1-3%, MgO 8-15%, AlN 5-15%, LOI 0.1-1%.

[0055] Specifically, aluminum slag is the white slag collected floating on the surface of molten aluminum during the process of alumina electrolysis and recycled aluminum production. Its main component is Al2O3. The original aluminum slag contains aluminum nitride, which will catalyze the production of a significant amount of ammonia when it comes into contact with water.

[0056] To further illustrate, calculated by mass percentage, the phosphogypsum includes the following chemical components: CaO35-45%, SiO2 1-3%, Al2O3 0.1-1%, Fe2O3 0.1-1%, SO3 50-60%, F 0.5-1.2%, P2O5 1-3%, and LOI 1-5%.

[0057] Specifically, phosphogypsum is an industrial byproduct discharged during the production of wet phosphoric acid. Its main components are calcium sulfate dihydrate and some impurities, including soluble phosphorus, fluorine and heavy metals. Because some phosphates and fluorides that replace sulfate ions in the crystal structure of phosphogypsum to form solid solutions are difficult to remove, the large-scale use of phosphogypsum is limited. This technical solution uses petroleum hydrocarbon contaminated soil to calcine phosphogypsum, and dihydrate gypsum is converted into hemihydrate gypsum, and does not form a solid solution with phosphates and fluorides, thereby releasing impurities such as phosphates and fluorides from the crystal structure. These water-soluble phosphates and fluorides are washed by calcium oxide to form insoluble phosphates and fluorides, and will not significantly affect the hydration reaction. In addition, the sulfate component in phosphogypsum can form needle-shaped calcium aluminate with hydrated calcium aluminate, filling the pores of the soil, optimizing the pore structure, and further improving the density of the soil.

[0058] Further explanation, calculated by mass percentage, the recycled pulp mud includes the following chemical components: CaO 57-65%, SiO2 1-4%, Al2O3 1-2%, Fe2O3 5-8%, Na2O 9-17%, Cr2O3 0.2-0.25%, CuO 0.13-0.19%, MgO 1-2%, LOI 5-14%. Among them, the main component of the recycled pulp mud is calcium carbonate. Since calcium carbonate is an unstable compound, it is easy to decompose into calcium oxide (CaO). If the content of calcium carbonate in the recycled pulp mud is directly detected, it is easy to cause inaccurate content detection. Therefore, when the chemical composition of the recycled pulp mud is detected in this technical solution, the calcium oxide content in the recycled pulp mud is mainly analyzed, and the calcium oxide content is used to represent the calcium carbonate content in the recycled pulp mud. Through conversion, it can be known that the calcium carbonate content in the recycled pulp mud of this technical solution is also 57-65%.

[0059] Pulp recycling mud is a byproduct produced in the process of recycling pulp. There are impurities such as heavy metals and calcium carbonate in the pulp recycling mud. The presence of these impurities significantly increases the economic cost of its resource utilization and limits its reuse as a resource. Therefore, pulp recycling has been mainly disposed of as waste directly by open-air stacking or on-site landfill without proper treatment and transformation. Pulp recycling mud contains a large number of fine fibers, which can increase the friction between soil particles and improve the shear strength of improved soil. The main component of pulp recycling mud is calcium carbonate, which forms calcium oxide after calcination. It can be used as a water-soluble phosphate cleaning agent and convert the water-soluble phosphate formed by calcined phosphogypsum into insoluble calcium phosphate without significantly affecting the hydration reaction. In addition, the hydration of calcium oxide formed by calcined pulp recycling mud can provide an alkaline environment, promote the formation of cementitious products such as hydrated calcium silicate and hydrated calcium aluminate, and further improve the bearing capacity of improved soil.

[0060] Further explanation, the particle size of the ceramic blank waste powder is ≤75μm; more preferably, the particle size of the ceramic blank waste powder is 30μm to 55μm. The physical filling effect of the ceramic blank waste powder can fill the pores between soil particles, thereby improving the density of the soil.

[0061] The particle size of the aluminum smelting white slag is ≤75μm; more preferably, the particle size of the aluminum smelting white slag is 60μm~70μm. When the original aluminum smelting white slag comes into contact with water or water vapor, a large amount of ammonia gas is generated, which can react with the sulfur dioxide gas generated during the calcination process of phosphogypsum, reduce harmful gas emissions, and avoid secondary pollution.

[0062] The particle size of the phosphogypsum is ≤75 μm; more preferably, the particle size of the phosphogypsum is 65 μm to 75 μm.

[0063] The particle size of the recycled pulp mud is ≤900 μm. More preferably, the particle size of the recycled pulp mud is 750 μm to 900 μm.

[0064] As a further explanation, in step (2), the bottom of the contaminated soil layer is preheated at a temperature of 450 to 550° C. for a preheating time of 1 to 2 hours.

[0065] Further explanation, in step (1), the amount of solid waste added is 8% to 14% of the mass of the petroleum hydrocarbon contaminated soil, calculated by mass percentage. Within this amount range, after combustion, improved soil with a compact structure and good water stability can be obtained.

[0066] The technical solution of the present invention is further described below through examples and comparative examples.

[0067] Example 1

[0068] The method of preparing improved soil by using petroleum hydrocarbon contaminated soil and multi-source solid waste in this embodiment includes the following steps:

[0069] (1) Pour the waste powder of ceramic embryo material, aluminum smelting slag, phosphogypsum and paper pulp recovery mud into an automatic vibrating screen for screening respectively, set the timer to 6 minutes and then start the automatic vibrating screen, the vibration amplitude of the vibrating screen is 8mm, the number of vibrations is 147 / min, the number of sieve shaking is 221 / min, and the rotation radius is 12.5mm. The sieved waste powder of ceramic embryo material, aluminum smelting slag, phosphogypsum and paper pulp recovery mud are mixed together to form a solid waste material, wherein the mixing method is to stir at 300rpm for 2min, adjust the speed to 1000rpm and stir for 2min to form a solid waste material; wherein, calculated by mass, the solid waste material consists of 35 parts of waste powder of ceramic embryo material, 20 parts of aluminum smelting slag, 15 parts of phosphogypsum and 30 parts of paper pulp recovery mud;

[0070] The petroleum hydrocarbon contaminated soil is laid as a bottom layer in the calcining chamber, and the pile height is 40 cm. The solid waste material is laid on the top surface of the petroleum hydrocarbon contaminated soil, and the pile height of the solid waste material is 5 cm. The petroleum hydrocarbon contaminated soil layer and the solid waste material layer are sequentially formed from bottom to top in the calcining chamber;

[0071] (2) Air with a flow rate of V1 (1.5 cm / s) is introduced into the petroleum hydrocarbon contaminated soil layer from the bottom of the calcination chamber by a blower, and then the bottom of the petroleum hydrocarbon contaminated soil layer is preheated, and the temperature is controlled to 500°C for a preheating time of 2 hours; when the temperature at 0 cm of the petroleum hydrocarbon contaminated soil layer reaches 500°C and the temperature at 20 cm reaches 450°C, the heating is stopped and the air flow rate is adjusted to V2 (4.0 cm / s) to make the petroleum hydrocarbon contaminated soil burn from bottom to top;

[0072] (3) When the temperature at each height of the calcination chamber (i.e., 0 cm, 20 cm, 40 cm, and 60 cm) is lower than 300° C., the calcined product is scraped out into a cooling furnace and cooled to room temperature, and the optimum moisture content of the calcined product is determined by referring to the method for determining the optimum moisture content in JTG 3441-2024 "Testing Procedure for Stabilized Materials of Inorganic Binders for Highway Engineering";

[0073] (4) According to the optimum moisture content, the amount of water to be added to the calcined product is calculated, and the required water is sprayed into the cooled calcined product by spraying. After spraying, the product is stirred at 300 rpm for 2 min, and then the rotation speed is adjusted to 1000 rpm and stirred for 2 min to obtain improved soil.

[0074] Among the above materials, the particle sizes of ceramic blank waste powder, aluminum smelting white slag and phosphogypsum are all ≤75μm (i.e., the undersize powder after sieving through a sieve with a mesh size of 75μm), and the particle size of pulp recovery mud is ≤900μm (i.e., the undersize material after sieving through a sieve with a mesh size of 900μm);

[0075] Calculated by mass percentage, the chemical composition of the ceramic blank waste powder in this embodiment includes: CaO 2.17wt%, SiO2 73.66wt%, Al2O3 15.35wt%, Fe2O3 2.49wt%, Na2O 1.46wt%, MgO 2.78wt%, LOI 2.09wt%. The chemical composition of aluminum smelting white slag includes: CaO 1.51wt%, SiO2 5.39wt%, Al2O3 70.92wt%, Fe2O3 2.54wt%, MgO 9.17wt%, AlN 9.82wt%, LOI 0.65wt%. The chemical composition of phosphogypsum includes: CaO41.38wt%, SiO2 1.45wt%, Al2O3 0.25wt%, Fe2O30.49wt%, SO3 52.98wt%, F 0.90wt%, P2O5 1.41wt%, LOI 1.14wt%. The chemical composition of recycled pulp mud is: CaO 62.75wt%, SiO2 3.71wt%, Al2O3 1.08wt%, Fe2O3 6.24wt%, Na2O 15.28wt%, Cr2O3 0.20wt%, CuO 0.14wt%, MgO1.82wt%, LOI 8.78wt%.

[0076] Example 2

[0077] The method for preparing improved soil by using petroleum hydrocarbon contaminated soil and multi-source solid waste in this embodiment is basically the same as that in Example 1, except that: calculated by mass, the solid waste materials in this embodiment are composed of 30 parts of ceramic embryo waste powder, 25 parts of aluminum smelting white slag, 20 parts of phosphogypsum and 25 parts of pulp recovery mud.

[0078] Example 3

[0079] The method for preparing improved soil by using petroleum hydrocarbon contaminated soil and multi-source solid waste in this embodiment is basically the same as that in Example 1, except that: in step (1), the pile height of the solid waste material is 10 cm.

[0080] Comparative Example 1

[0081] The method for preparing improved soil in this comparative example is basically the same as that in Example 1, except that: in this comparative example, solid waste materials are not laid on the surface of the petroleum hydrocarbon contaminated soil in step (1), but the solid waste materials are directly added to the calcined product after cooling in step (4), that is, the solid waste materials in this comparative example are not calcined.

[0082] Comparative Example 2

[0083] The method for preparing improved soil in this comparative example is basically the same as that in Example 1, except that: in this comparative example, solid waste materials are not laid on the surface of the petroleum hydrocarbon contaminated soil in step (1), but the solid waste materials are directly added to the calcined product after cooling in step (4), that is, the solid waste materials in this comparative example are not calcined, and the number of solid waste materials added in this comparative example is equivalent to the solid waste materials with a pile height of 10 cm.

[0084] Comparative Example 3

[0085] In this comparative example, PO42.5 cement is used as a curing agent to improve the calcined petroleum hydrocarbon contaminated soil. The cement is ordinary Portland cement, and its basic properties are shown in Table 1. The amount of cement added in this comparative example is equivalent to the amount of the pile height of 5 cm.

[0086] Comparative Example 4

[0087] In this comparative example, PO42.5 cement is used as a curing agent to improve the calcined petroleum hydrocarbon contaminated soil. The cement is ordinary Portland cement, and its basic properties are shown in Table 1. The amount of cement added in this comparative example is equivalent to the amount of the pile height of 10 cm.

[0088] Table 1 Physical properties of cement used in the test

[0089]

[0090] The petroleum hydrocarbon contaminated soil was improved by the methods of Examples 1 to 3 and Comparative Examples 1 to 4 respectively, and the specific steps were as follows:

[0091] (1) Soil collection

[0092] The soil samples were taken from a lubricating oil base oil production plant in Foshan City. The excavation depth was 5m. The basic performance indicators of the soil samples are shown in Table 2.

[0093] Table 2 Basic properties of soil samples

[0094]

[0095] (2) Improved soil

[0096] The improved soil molding and test methods refer to JTG 3441-2024 "Testing Procedures for Stabilized Materials of Inorganic Binders for Highway Engineering". After molding, the samples were immediately sealed in polyethylene bags and placed in a standard curing room [(20±5)℃, humidity>95%RH] for curing. The unconfined compressive strength, permeability coefficient and shrinkage coefficient of the samples with a curing time of 7 days, 14 days and 28 days were tested. The test results are shown in Table 3.

[0097] Table 3 Test results of various test properties of improved soil samples

[0098]

[0099] Note: ND means not detected

[0100] Furthermore, the improved soil leaching toxicity test and petroleum hydrocarbon content test were carried out. The test methods refer to: "Solid Waste Leaching Toxicity Leaching Method Horizontal Oscillation Method" (HJ577-2010) and "Soil Petroleum Determination Infrared Spectrophotometry" (HJ1051-2019). The broken test pieces were tested after the 28-day unconfined compressive strength test. The test results are shown in Table 4.

[0101] Table 4 Test results of heavy metal and petroleum hydrocarbon content in improved soil samples

[0102]

[0103]

[0104] It can be seen from the test results of Tables 3 and 4 above that the technical solution uses the high calorific value organic matter present in the petroleum hydrocarbon contaminated soil as fuel, and uses the combustion of the pollutants themselves to trigger the continuous combustion of the surrounding areas. While removing the pollutants, the high-temperature calcination can stimulate the activity of the solid waste materials, and the solid waste materials gradually sinter and change from loose to densely structured clinker. After the calcined petroleum hydrocarbon contaminated soil-solid waste material mixture is added with water and stirred and mixed at the optimal moisture content, the active substances in the calcined pulp recovery mud react with water to generate alkaline substances, providing an alkaline environment for the active silicon and aluminum phases in the ceramic embryo waste powder and the aluminum slag, promoting the formation of cementitious products such as hydrated calcium silicate and hydrated calcium aluminate, cementing soil particles, refining the pores of soil particles, and forming a skeleton structure. At the same time, the sulfate ions in the phosphogypsum can react with the hydrated calcium aluminate to generate needle-shaped calcium aluminate in an alkaline environment, filling the pores between the soil particles, further improving the soil density, and forming a dense structure and improved soil with good water stability. This technical solution makes full use of large amounts of solid waste such as ceramic embryo powder, aluminum slag, phosphogypsum, and pulp recovery mud, alleviating the resource and environmental pressures caused by the accumulation of solid waste. The solid waste materials are thermally activated by the heat of petroleum hydrocarbon combustion, which reduces the extra energy consumption of mechanical grinding and avoids chemical stimulation such as acid stimulation and alkali stimulation that may damage the acid-base balance of the soil. The present invention utilizes petroleum hydrocarbon contaminated soil in conjunction with multi-source solid waste to prepare improved soil, which can improve the density and compressive strength of the soil, and can also solidify and stabilize heavy metal ions.

[0105] The above disclosure is only the preferred embodiment of the present invention, which certainly cannot be used to limit the scope of the present invention. Therefore, equivalent changes made according to the claims of the present invention are still within the scope of the present invention.

Claims

1. A method for preparing improved soil by using petroleum hydrocarbon contaminated soil and multi-source solid waste, characterized in that: The steps include: (1) laying petroleum hydrocarbon contaminated soil in a calcining chamber, laying solid waste materials on the top surface of the petroleum hydrocarbon contaminated soil, and forming a petroleum hydrocarbon contaminated soil layer and a solid waste material layer in sequence from bottom to top inside the calcining chamber; the components of the solid waste materials include ceramic blank waste powder, aluminum smelting white slag, phosphogypsum and pulp recovery mud; (2) introducing air at a flow rate of V1 from the bottom of the petroleum hydrocarbon contaminated soil layer into the petroleum hydrocarbon contaminated soil layer, and then preheating the bottom of the petroleum hydrocarbon contaminated soil layer. When the temperature of the bottom of the petroleum hydrocarbon contaminated soil layer reaches the ignition point of the petroleum hydrocarbon compounds in the petroleum hydrocarbon contaminated soil, the heating is stopped, and the flow rate of the air is adjusted to V2, so that the petroleum hydrocarbon contaminated soil burns from bottom to top; Wherein, V2 = (1.5-4.5) V1; (3) When the temperature of the calcination chamber is lower than 300°C, pour out the calcined product and cool it to room temperature; (4) Add water to the cooled calcined product and stir evenly to obtain improved soil.

2. The method for preparing improved soil by using petroleum hydrocarbon contaminated soil and multi-source solid waste according to claim 1, characterized in that: In step (2), V1 is 1.0-2.0 cm / s; V2 is 3.0-4.5 cm / s.

3. The method for preparing improved soil by using petroleum hydrocarbon contaminated soil and multi-source solid waste according to claim 1, characterized in that: The content of petroleum hydrocarbon pollutants in the petroleum hydrocarbon contaminated soil is 1500-3500 mg / L.

4. The method for preparing improved soil by using petroleum hydrocarbon contaminated soil and multi-source solid waste according to claim 1, characterized in that: Calculated by weight, the components of the solid waste material include 30-35 parts of ceramic embryo waste powder, 20-30 parts of aluminum smelting white slag, 15-20 parts of phosphogypsum and 25-30 parts of pulp recovery mud; In step (1), the amount of solid waste material added is 8% to 14% of the mass of the petroleum hydrocarbon contaminated soil, calculated as a percentage by mass.

5. The method for preparing improved soil by using petroleum hydrocarbon contaminated soil and multi-source solid waste according to claim 1, characterized in that: Calculated by mass percentage, the ceramic blank waste powder includes the following chemical components: CaO 1-5%, SiO2 60-75%, Al2O3 12-21%, Fe2O3 1-3%, Na2O 1-3%, MgO 1-5%, and LOI 2-5%.

6. The method for preparing improved soil by using petroleum hydrocarbon contaminated soil and multi-source solid waste according to claim 1, characterized in that: Calculated by mass percentage, the aluminum smelting white slag includes the following chemical components: CaO 1-2%, SiO2 2-6%, Al2O3 68-77%, Fe2O3 1-3%, MgO 8-15%, AlN 5-15%, and LOI 0.1-1%.

7. The method for preparing improved soil by using petroleum hydrocarbon contaminated soil and multi-source solid waste according to claim 1, characterized in that: Calculated by mass percentage, the phosphogypsum includes the following chemical components: CaO 35-45%, SiO2 1-3%, Al2O3 0.1-1%, Fe2O3 0.1-1%, SO3 50-60%, F 0.5-1.2%, P2O5 1-3%, and LOI 1-5%.

8. The method for preparing improved soil by using petroleum hydrocarbon contaminated soil and multi-source solid waste according to claim 1, characterized in that: Calculated by mass percentage, the recycled pulp mud includes the following chemical components: CaO 57-65%, SiO2 1-4%, Al2O3 1-2%, Fe2O3 5-8%, Na2O 9-17%, Cr2O3 0.2-0.25%, CuO 0.13-0.19%, MgO 1-2%, and LOI 5-14%.

9. The method for preparing improved soil by using petroleum hydrocarbon contaminated soil and multi-source solid waste according to claim 1, characterized in that: The particle size of the ceramic blank waste powder is ≤75 μm; The particle size of the aluminum smelting white slag is ≤75 μm; The particle size of the phosphogypsum is ≤75 μm; The particle size of the recycled pulp sludge is ≤900 μm.

10. The method for preparing improved soil by using petroleum hydrocarbon contaminated soil and multi-source solid waste according to claim 1, characterized in that: In step (2), the bottom of the contaminated soil layer is preheated at a temperature of 450 to 550° C. for a preheating time of 1 to 2 hours.

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