A method for treating petroleum-contaminated soil

Abstract

The application provides a method for treating oil-contaminated soil. The inhibitor used in the method comprises diallyl dimethyl ammonium chloride, carboxymethyl polyethylene polyamine, polyvinyl alcohol, ammonium bicarbonate, polyethylene glycol, calcium oxide and alkali metal oxide. The method comprises washing and screening the oil-contaminated soil to divide it into a low-oil-content part and a high-oil-content part. The low-oil-content part is treated by using the inhibitor to obtain a first treated soil. The high-oil-content part is treated by using a dispersion promoter and a cleaning agent to obtain a second treated soil. The first treated soil and the second treated soil are combined and subjected to flotation treatment to separate out soil and obtain the soil after the flotation treatment.

Description

Technical Field

[0001] This invention relates to the field of oil-contaminated soil treatment, and particularly to the graded treatment of oil-contaminated soil. Background Technology

[0002] Oil-contaminated soil refers to soil polluted by leaks and spills during oil extraction and transportation. Oil pollution not only damages soil structure and deteriorates the living environment, but also threatens human health. Despite numerous control measures implemented in recent years, soil pollution remains a serious problem in my country.

[0003] The degree of oil contamination in soil varies, requiring different treatment technologies and incurring varying costs. Generally, the higher the degree of contamination, the higher the treatment cost. Oil-contaminated soil remediation technologies mainly include pyrolysis, chemical oxidation, extraction, chemical cleaning, and biological methods. Specifically, low-contamination oil-contaminated soil with an oil content ≤2% is suitable for treatment using microbial remediation and phytoremediation; moderately contaminated oil-contaminated soil with an oil content of 2% to 5% is suitable for treatment using chemical oxidation, bioremediation, and thermal desorption; and highly contaminated oil-contaminated soil with an oil content ≥5% is suitable for treatment using chemical cleaning, pyrolysis, thermal desorption, and extraction.

[0004] Chemical cleaning technology offers advantages such as recoverable petroleum resources, ease of operation, cost-effectiveness, and broad applicability, making it one of the mainstream treatment technologies both domestically and internationally. Chemical cleaning uses chemical detergents to desorb and remove crude oil contaminants adsorbed on soil particles, followed by separation of the soil, water, and oil phases through methods such as gravity settling or centrifugation. Current petroleum-contaminated soil cleaning technologies, to improve cleaning efficiency, involve feeding the contaminated soil into a slurry tank where mechanical stirring or ultrasonic assistance breaks up the oil-soil mixture into a homogeneous fine slurry, promoting contact between the soil and the cleaning agent. Summary of the Invention

[0005] The inventors of this invention discovered through research that soil pollution exhibits heterogeneous characteristics. When oil enters the soil, it adheres to the soil surface in a multi-layered, stacked manner, then permeates and fills the pores. Oil molecules easily adhere to each other; therefore, heavily polluted soil particles covered by oil tend to clump together, forming large, dense oil-soil particles. Meanwhile, some unpolluted or less polluted soil particles remain in their original, loose, small particle state. Existing technologies do not consider the heterogeneous characteristics of polluted soil and directly employ homogenization methods. This results in some low-oil-content soil or unpolluted soil being uniformly homogenized and mixed with high-oil-content soil. This not only contaminates some unpolluted soil but also causes low-oil-content soil that does not require washing to be washed, increasing the amount of washing treatment, the dosage of washing agents, and heating energy consumption.

[0006] Therefore, one aspect of the present invention provides an inhibitor comprising diallyl dimethyl ammonium chloride, carboxymethyl polyethylene polyamine, polyvinyl alcohol, ammonium bicarbonate, polyethylene glycol, calcium oxide, and alkali metal oxides.

[0007] In one specific embodiment, the number-average molecular weight of the polyvinyl alcohol is between 120,000 and 220,000.

[0008] In one specific embodiment, the number-average molecular weight of the polyethylene glycol is 1000 to 2000.

[0009] In one specific embodiment, the alkali metal oxide is potassium oxide and / or sodium oxide.

[0010] In one specific embodiment, based on the total mass of the inhibitor as 100%, the diallyl dimethyl ammonium chloride is 2% to 5%, carboxymethyl polyethylene polyamine is 5% to 10%, polyvinyl alcohol is 5% to 10%, ammonium bicarbonate is 50% to 80%, polyethylene glycol is 2% to 5%, calcium oxide is 3% to 10%, and alkali metal oxide is 3% to 10%.

[0011] The second aspect of the present invention provides a method for treating petroleum-contaminated soil, comprising washing and screening the petroleum-contaminated soil to separate it into a low-oil-content fraction and a high-oil-content fraction; wherein, the low-oil-content fraction is treated with an inhibitor as described in any one of the present invention to obtain a first-treated soil; the high-oil-content fraction is treated with a dispersant and a cleaning agent to obtain a second-treated soil; the first-treated soil and the second-treated soil are combined and subjected to flotation treatment to separate the soil, thereby obtaining flotation-treated soil.

[0012] In one specific embodiment, the method includes the following steps;

[0013] 1) The petroleum-contaminated soil was mixed with the first washing solution to obtain mud 1;

[0014] 2) The mud 1 is sieved in the second washing liquid using the first sieve to obtain mud with low oil content under the sieve and soil particles with high oil content on the sieve.

[0015] 3) Dry the high-oil-content soil particles, add a dispersion accelerator, mix and disperse, and sieve using a second sieve to obtain small high-oil-content soil particles smaller than the aperture of the second sieve and large high-oil-content soil particles larger than the aperture of the second sieve; add the dispersion accelerator to the large high-oil-content soil particles larger than the aperture of the second sieve, mix and disperse, and sieve using the second sieve to obtain small high-oil-content soil particles smaller than the aperture of the second sieve; if there are still large high-oil-content soil particles larger than the aperture of the second sieve, continue to add the dispersion accelerator, mix and disperse, and sieve using the second sieve until all large high-oil-content soil particles are smaller than the aperture of the second sieve after treatment, thus obtaining dispersed high-oil-content soil particles;

[0016] 4) The high-oil-content soil dispersion particles are mixed with the third washing solution and cleaning agent to obtain mud slurry 2;

[0017] 5) Mix the screened mud with the inhibitor to obtain mud 3;

[0018] 6) Mix the mud 2 and the mud 3 to obtain mud 4; subject the mud 4 to flotation treatment to obtain scum and mud 5, wherein the scum is removed from the mud 5;

[0019] 7) The mud 5 is subjected to solid-liquid separation, wherein the solid phase is the treated soil.

[0020] In one specific embodiment, in step 1), the mass ratio of the petroleum-contaminated soil to water is 1:(1 to 3), and after mixing, the soil is soaked for 2 to 4 hours to obtain the mud 1.

[0021] In one specific embodiment, the aperture of the first and second sample sieves is 1 to 3 mm.

[0022] In one specific embodiment, the temperature of the second washing solution is 50 to 70°C.

[0023] In one specific embodiment, the temperature at which the mud 2 is prepared is 50 to 60°C.

[0024] In one specific embodiment, the first sampling sieve is placed above the surface of the second washing liquid, the mud slurry 1 is poured into the first sampling sieve, the first sampling sieve is covered with the sampling sieve cover, and the first sampling sieve and the sampling sieve cover are fixed. The first sampling sieve is then submerged in the second washing liquid and then lifted out. This process is repeated 10 to 20 times to obtain the low oil content undersize mud slurry and the high oil content soil particles on the sieve.

[0025] In one specific embodiment, the initial addition amount of the dispersion promoter is 3% to 8% based on the mass of the high oil content soil particles, wherein the moisture content of the high oil content soil particles is 13% to 18%, for example, the moisture content of the high oil content soil particles is 13.2% to 16.5%.

[0026] In one specific embodiment, the subsequent addition of the dispersion promoter is 1% to 5%, based on the mass of the large particles in the high-oil-content soil as 100%.

[0027] In one specific embodiment, the mass ratio of the high oil content soil dispersion particles to the third washing liquid is 1:(2 to 5).

[0028] In one specific embodiment, the amount of the cleaning agent is 3% to 8%, calculated as 100% of the total mass of the high-oil-content soil dispersion particles and the third washing solution.

[0029] In one specific embodiment, the amount of the inhibitor is 5% to 10%, based on the mass of the screened slurry as 100%.

[0030] In one specific embodiment, the height of the second washing solution is 3 to 6 times the height of the first sampling sieve.

[0031] In one specific embodiment, the dispersion promoter includes calcium chloride, calcium oxide, and quartz sand.

[0032] In one specific embodiment, the total mass of the dispersion promoter is 100%, the calcium chloride is 15% to 25% (e.g., 15% to 20%), the calcium oxide is 55% to 75% (e.g., 65% to 75%), and the quartz sand is 10% to 20%.

[0033] In one specific embodiment, the quartz sand has a mesh size of 60 to 200.

[0034] In one embodiment, the cleaning agent comprises potassium dialkyl alcohol ether carboxylate, sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, sodium silicate, sodium chloride, sodium hydroxide, and water.

[0035] In one specific embodiment, based on the total mass of the cleaning agent as 100%, the potassium dialkyl alcohol ether carboxylate is 3% to 7%, the sodium dodecyl sulfate is 5% to 10%, the sodium dodecylbenzene sulfonate is 5% to 15%, the sodium silicate is 3% to 10%, the sodium chloride is 3% to 5% (e.g., 3% to 4%), the sodium hydroxide is 1% to 5%, and the water is 48% to 80%.

[0036] In one specific embodiment, the first, second, and third rinsing solutions are independently water or the final aqueous phase collected after treating petroleum-contaminated soil.

[0037] The beneficial effects of this invention are:

[0038] 1. Taking into full account the heterogeneous characteristics of petroleum-contaminated soil, before cleaning and treatment, the high-oil-content and low-oil-content portions of the contaminated soil are separated to avoid the high-oil-content portion from contaminating the low-oil-content portion, thereby improving the applicability of the treatment technology, increasing the treatment accuracy, and reducing the treatment difficulty and energy consumption.

[0039] First, the oil-contaminated soil is soaked, then washed and screened. Large, compact, high-oil-content soil particles are trapped on the screen, while small, low-oil-content soil particles pass through the screen, separating the oil-contaminated soil into a high-oil-content large-particle portion and a low-oil-content small-particle portion.

[0040] The high-oil-content portion has a high oil content, generally greater than 5%, and can be recycled as a petroleum resource. The low-oil-content portion has a low oil content, and may even contain a large portion of clean, uncontaminated soil particles, with an average oil content of less than 5%. Therefore, this portion of soil does not require washing and can undergo microbial remediation to ultimately achieve harmless treatment.

[0041] 2. For soils with high oil pollution, a dispersing accelerator is added in a dry state to disperse large particles into smaller particles, and then water and cleaning agents are added for cleaning treatment.

[0042] Because of the viscosity of petroleum, oil-contaminated soil particles are tightly bound together. Petroleum is mainly concentrated in the high-oil-content soil particles on the sieve. Complex physical and chemical reactions occur as the soil particles adhere to the petroleum, further tightening the bond and disrupting the original loose, porous soil structure. The soil particles, under the influence of crude oil, stick together to form stable oil-contaminated soil particles. In the process of cleaning oil-contaminated soil, the cleaning agent mainly acts on the external contaminants of the soil particles, removing the petroleum adsorbed around them. It cannot act on the interior of the soil particles. To remove the petroleum contaminants from the oil-contaminated soil particles, the particles must be broken up to fully expose the contaminated surface. High-oil-content soil particles are poorly dispersed when mixed with water; in fact, agitation in water can cause them to continue to agglomerate into larger oil-contaminated soil particles. Therefore, to break up these high-oil-content particles, a dispersing accelerator is added to the dry soil before cleaning. The accelerator absorbs water and disperses the large oil-contaminated soil particles into smaller ones. Water and cleaning agents are then added to the dispersed small oil-contaminated soil particles for further cleaning. In other words, directly adding water to contaminated soil and then homogenizing and breaking it up through vigorous stirring or ultrasonic waves results in particle adhesion and poor breaking effect. In this invention, the soil particles are first broken up by stirring under the action of a dispersing accelerator, and then water is added for washing, resulting in a better breaking effect.

[0043] 3. Add inhibitors to soils with low oil pollution.

[0044] A large portion of the low-oil-content soil particles are not contaminated by petroleum. To prevent these clean, uncontaminated soil particles from adsorbing petroleum from the washing solution and causing secondary pollution, an inhibitor is added to the low-oil-content soil. The inhibitor of this invention mainly inhibits the mutual adsorption between clay particles and petroleum particles, reducing the binding of petroleum particles and clay particles. Additionally, it inhibits the flocculation of clay in water, maintaining its granular shape and preventing it from floating to the surface with the crude oil during subsequent flotation. Detailed Implementation

[0045] The present invention will be further described below with reference to the embodiments. However, the embodiments of the present invention are merely illustrative examples and should not be construed as limiting the present invention under any circumstances.

[0046] Example 1

[0047] Based on the total mass of the inhibitor as 100%, 2% diallyl dimethyl ammonium chloride, 5% carboxymethyl triethylenetetramine, 5% polyvinyl alcohol with a number average molecular weight of 120,000, 80% ammonium bicarbonate, 2% polyethylene glycol with a number average molecular weight of 1,000, 3% calcium oxide powder, and 3% potassium oxide powder were mixed evenly to obtain inhibitor #1.

[0048] Example 2

[0049] Based on the total mass of the inhibitor as 100%, 3% diallyl dimethyl ammonium chloride, 7% carboxymethyl triethylenetetramine, 8% polyvinyl alcohol with a number average molecular weight of 160,000, 65% ammonium bicarbonate, 3% polyethylene glycol with a number average molecular weight of 1,500, 6% calcium oxide powder, and 5% sodium oxide powder were mixed evenly to prepare inhibitor #2.

[0050] Example 3

[0051] Based on the total mass of the inhibitor as 100%, 5% diallyl dimethyl ammonium chloride, 10% carboxymethyl triethylenetetramine, 10% polyvinyl alcohol with a number average molecular weight of 220,000, 50% ammonium bicarbonate, 5% polyethylene glycol with a number average molecular weight of 2,000, 10% calcium oxide powder, and 10% potassium oxide powder were mixed evenly to obtain inhibitor #3.

[0052] Preparation of Dispersion Accelerator

[0053] Example 4

[0054] Dispersion accelerator 1# is prepared by uniformly mixing 15wt% anhydrous calcium chloride, 75wt% calcium oxide, and 10wt% ordinary quartz sand with a mesh size of 200 mesh.

[0055] Example 5

[0056] Dispersion accelerator 2# is prepared by uniformly mixing 25wt% anhydrous calcium chloride, 55wt% calcium oxide, and 20wt% ordinary quartz sand with a mesh size of 60.

[0057] Example 6

[0058] Dispersion accelerator 3# is prepared by uniformly mixing 20wt% anhydrous calcium chloride, 65wt% calcium oxide, and 15wt% ordinary quartz sand with a mesh size of 150.

[0059] Preparation of cleaning agent

[0060] Example 7

[0061] Cleaning agent #1 is prepared by mixing 3 wt% potassium dodecyl alcohol ether carboxylate, 5 wt% sodium dodecyl sulfate, 5 wt% sodium dodecylbenzene sulfonate, 3 wt% sodium silicate, 3 wt% sodium chloride, 1 wt% sodium hydroxide, and 80 wt% water evenly.

[0062] Example 8

[0063] Cleaning agent #2 is prepared by mixing 5 wt% potassium dodecyl alcohol ether carboxylate, 7 wt% sodium dodecyl sulfate, 10 wt% sodium dodecylbenzene sulfonate, 8 wt% sodium silicate, 4 wt% sodium chloride, 3 wt% sodium hydroxide, and 63 wt% water evenly.

[0064] Example 9

[0065] Cleaning agent #3 was prepared by mixing 7 wt% potassium dodecyl alcohol ether carboxylate, 10 wt% sodium dodecyl sulfate, 15 wt% sodium dodecylbenzene sulfonate, 10 wt% sodium silicate, 5 wt% sodium chloride, 5 wt% sodium hydroxide, and 48 wt% water evenly.

[0066] Oil-contaminated soil treatment

[0067] The oil content of soil was determined by extraction. A certain mass of air-dried soil was accurately weighed, wrapped in filter paper, and chloroform was used as the extractant. The soil was refluxed and extracted for 6 hours using a Soxhlet extractor. After extraction, the chloroform was transferred to a beaker of constant weight and dried at 75°C until the chloroform was completely evaporated to obtain the extracted crude oil. The amount of extracted crude oil was weighed, and the mass percentage of crude oil in the tested soil was calculated and recorded as the soil oil content.

[0068] Soil moisture content was determined by the gravimetric method. A certain mass of soil sample was placed in an oven at 103℃ and dried to constant weight. The percentage decrease in mass was recorded as the moisture content.

[0069] Example 10

[0070] Oil spills at Shengli Oilfield well site contaminate soil

[0071] In this example, the soil to be treated is petroleum-contaminated soil from the Shengli Oilfield well site, with an oil content of 7.6% and a water content of 5.9%.

[0072] 1) Take 250g of the petroleum-contaminated soil sample to be treated, add 250g of clean water as the first washing solution, let stand and soak at room temperature for 2 hours to obtain mud 1.

[0073] 2) Washing and screening mud 1: Take a bucket with a diameter of 40cm and a height of 30cm, add 50℃ clean water to the bucket as the second washing solution, the water depth is 15cm, which is 3 times the height of the sampling sieve; place a stainless steel standard sampling sieve with a 2mm aperture on the surface of the second washing solution, the sampling sieve has a diameter of 20cm and a height of 5cm; after pouring all of mud 1 onto the surface of the sampling sieve, sink the sampling sieve into the second washing solution, then lift it up, repeat 15 times, place the sampling sieve on the surface of the second washing solution, drain the water until no liquid drips; after screening, mud 1 is divided into undersize mud slurry and oversize product. Soil particles with a diameter of <2mm and some crude oil enter the second washing liquid, which is called undersize mud. The oversize product is soil particles with a diameter of ≥2mm on the screen surface. After testing, the oil content of soil particles with a diameter of <2mm in the undersize mud is 3.46%, which is called low oil content soil particles. The oil content of soil particles with a diameter of ≥2mm in the oversize product is 9.86%, which is called high oil content soil particles.

[0074] 3) Transfer the high-oil-content soil particles to a ventilated area and air-dry them until the moisture content is 15.8%. After air-drying, the high-oil-content soil particles weigh 123g. Add 3.69g of dispersion accelerator 1#, that is, the addition amount of dispersion accelerator 1# is 3% of the mass of the high-oil-content soil particles. Stir and mix the high-oil-content soil particles with dispersion accelerator 1#. After the high-oil-content soil particles are gradually dispersed, they are sieved using a 2mm aperture sieve. After sieving, there are still 20.8g of high-oil-content soil particles with a diameter greater than 2mm. Add 1% of the mass of dispersion accelerator 1# to this part of the high-oil-content soil particles, stir and mix to disperse. After dispersion, sieve again using a 2mm aperture sieve. At this time, all high-oil-content soil particles are dispersed into particles with a diameter <2mm, which are called high-oil-content soil dispersed particles. If there are still soil particles with a diameter greater than 2 mm, it is necessary to continue adding dispersion promoter 1# and dispersing and sieving until all high oil content soil particles are dispersed into particles with a diameter of < 2 mm.

[0075] 4) Water was added sequentially to the high-oil-content soil dispersion particles as the third washing solution and cleaning agent 1#. The amount of water added was twice the mass of the high-oil-content soil dispersion particles, and the amount of cleaning agent 1# added was 3% of the total mass of the high-oil-content soil dispersion particles and water. The mixture was stirred and mixed at a constant temperature of 50℃ to obtain mud 2. A forced electric mixer with a power of 120W was used for stirring. The mixing paddle was a two-blade paddle type, and the mixing paddle and blades were made of stainless steel. The stirring speed was 200r / min, and the stirring time was 60min.

[0076] 5) Add inhibitor 1# to the sieved mud to obtain mud 3. The amount of inhibitor 1# added is 5% of the mass of the sieved mud. After adding inhibitor 1#, stir at a speed of 120 r / min for 10 min.

[0077] 6) After mixing mud 2 and mud 3, mud 4 is obtained. Mud 4 is then subjected to flotation treatment to obtain scum and mud 5. The flotation treatment uses a single-cell flotation machine with a motor power of 180W, an impeller diameter of 45mm, an impeller speed of 2590r / min, a scraper speed of 30r / min, and a flotation time of 10min. Petroleum contaminants in mud 4, i.e., aged crude oil, float to the surface during the air flotation process, forming scum. The scum is scraped away and collected for resource recovery. The system after removing the scum is mud 5.

[0078] 7) The mud slurry 5 was centrifuged and dewatered using a two-phase centrifuge at 3000 rpm for 8 minutes, yielding an aqueous phase and a solid phase. The aqueous phase can be collected and recycled as washing liquid. The solid phase is the treated soil with an oil content of 1.05%, weighing 175.0 g after drying, with a soil loss of 43.1 g. Further harmless treatment can be carried out using bioremediation, phytoremediation, or other methods.

[0079] Comparative Example 1

[0080] Step 5 is omitted; all other steps are the same as in Example 10. The soil without inhibitor treatment had an oil content of 2.41%, weighed 145.0 g after drying, and suffered a soil loss of 74.8 g. Compared to the soil with inhibitor, the treated soil had a higher oil content and a greater soil mass loss, indicating that some soil adhered to the crude oil and floated to the surface with it during flotation.

[0081] Example 11

[0082] Oil spills at Shengli Oilfield well site contaminate soil

[0083] In this example, the soil to be treated is petroleum-contaminated soil from the Shengli Oilfield well site, with an oil content of 12.4% and a water content of 7.6%.

[0084] 1) Take 250g of the petroleum-contaminated soil sample to be treated, add 500g of water to the petroleum-contaminated soil, let it stand and soak at room temperature for 2 hours to obtain mud 1.

[0085] 2) Washing and sieving mud 1: Take a container with a diameter of 40cm and a height of 50cm, add 60℃ clean water as washing solution to the container, with a water depth of 20cm, which is 4 times the height of the sieve; place a stainless steel standard sieve with a 2mm aperture on the surface of the washing solution. The sieve has a diameter of 20cm and a height of 5cm. After pouring all of mud 1 onto the sieve surface, cover the sieve with the sieve cover and clamp the sieve cover and sieve together. Submerge the sieve in the washing solution, then lift it up. Repeat this process 20 times. Place the sieve on the surface of the washing solution and drain the water until no liquid drips. After sieving, mud 1 is separated into undersize mud slurry and oversize product. The undersize slurry is a mixture of petroleum-contaminated soil with a particle size <1mm and washing liquid in the container; the oversize product is soil particles with a particle size ≥1mm on the sieve surface; after testing, the soil particles with a particle size <1mm in the undersize slurry have an oil content of 4.01%, which are referred to as low-oil-content soil particles; the soil particles with a particle size ≥1mm in the oversize product have an oil content of 10.42%, which are referred to as high-oil-content soil particles.

[0086] 3) Transfer the high-oil-content soil particles to a ventilated area and air-dry them until the moisture content is 16.5%. After air-drying, the high-oil-content soil particles weigh 102g. Add 5.1g of dispersion accelerator #2, which is 5% of the mass of the high-oil-content soil particles. Mix the high-oil-content soil particles with dispersion accelerator #2. The high-oil-content soil particles gradually disperse and break into a loose state. Sieve them using a 1mm aperture sieve. After sieving, about 10% of the particles are still larger than 1mm. Add 3% of the mass of dispersion accelerator #2 to this portion of high-oil-content soil particles, mix and disperse. After dispersion, sieve again using a 1mm aperture sieve. At this point, all high-oil-content soil particles are dispersed into particles with a diameter <1mm, which are called high-oil-content soil dispersed particles.

[0087] 4) Add water and cleaning agent #2 sequentially to the high-oil-content soil dispersion particles. The amount of water added is 3 times the mass of the high-oil-content soil dispersion particles, and the amount of cleaning agent #2 added is 5% of the total mass of the high-oil-content soil dispersion particles and water. Mix under a constant temperature of 55℃ to obtain mud 2. The mixing is carried out using a forced electric mixer with a power of 120W. The mixing paddle is a two-blade paddle type, and the mixing paddle and blades are made of stainless steel. The mixing speed is 300r / min, and the mixing time is 40min.

[0088] 5) Add inhibitor 2# to the sieved mud to obtain mud 3. The amount of inhibitor 2# added is 8% of the mass of the sieved mud. After adding inhibitor 2#, stir and mix. The stirring is done with a forced electric mixer with a motor power of 120W. The stirring paddle is a two-blade paddle type. The stirring paddle and blades are made of stainless steel. The stirring speed is 60r / min and the stirring time is 30min.

[0089] 6) After mixing mud 2 and mud 3, mud 4 is obtained. Mud 4 is then subjected to flotation treatment to obtain scum and mud 5. The flotation treatment uses a single-cell flotation machine with a motor power of 180W, an impeller diameter of 45mm, an impeller speed of 2590r / min, a scraper speed of 30r / min, and a flotation time of 30min. The petroleum contaminants in mud 4, i.e., aged crude oil, float to the surface during the air flotation process to form scum. The scum is scraped away and collected for resource recovery. The system after removing the scum is mud 5.

[0090] 7) The mud slurry 5 was centrifuged and dewatered using a two-phase centrifuge at 3000 rpm for 5 minutes, yielding an aqueous phase and a solid phase. The aqueous phase can be collected and recycled as washing liquid. The solid phase is the treated soil with an oil content of 2.56%, weighing 163.8 g after drying, with a soil loss of 40.4 g. Further harmless treatment can be carried out using bioremediation, phytoremediation, or other methods.

[0091] Comparative Example 2

[0092] Step 5 is omitted; all other steps are the same as in Example 11. The soil without inhibitor treatment had an oil content of 3.48%, weighed 137.0 g after drying, and suffered a soil loss of 67.8 g. Compared to the soil with inhibitor, the treated soil had a higher oil content and a greater soil mass loss, indicating that some soil adhered to the crude oil and floated to the surface with it during flotation.

[0093] Example 12

[0094] Oil spills at Shengli Oilfield well site contaminate soil

[0095] In this example, the soil to be treated is petroleum-contaminated soil from the Shengli Oilfield well site, with an oil content of 18.6% and a water content of 7.9%.

[0096] 1) Take 250g of the petroleum-contaminated soil sample to be treated, add 750g of water to the petroleum-contaminated soil, let it stand and soak at room temperature for 2 hours to obtain mud 1.

[0097] 2) Washing and sieving mud 1: Take a container with a diameter of 40cm and a height of 50cm, add 70℃ clean water as washing solution to the container, with a water depth of 25cm, which is 5 times the height of the sieve; place a stainless steel standard sieve with a 2mm aperture on the surface of the washing solution. The sieve has a diameter of 20cm and a height of 5cm. After pouring all of mud 1 onto the sieve surface, cover the sieve with the sieve cover and clamp the sieve cover and sieve together. Submerge the sieve in the washing solution, then lift it up. Repeat this process 20 times. Place the sieve on the surface of the washing solution and drain the water until no liquid drips. After sieving, mud 1 is separated into undersize mud and oversize product. The undersize slurry is a mixture of petroleum-contaminated soil with a particle size <3mm and washing liquid in the container; the oversize product is soil particles with a particle size ≥3mm on the sieve surface; the oil content of the soil particles with a particle size <3mm in the undersize slurry is 4.20%, and they are referred to as low-oil-content soil particles; the oil content of the soil particles with a particle size ≥3mm in the oversize product is 12.81%, and they are referred to as high-oil-content soil particles.

[0098] 3) Transfer the high-oil-content soil particles to a ventilated area and air-dry them until the moisture content is 13.2%. After air-drying, the high-oil-content soil particles weigh 144g. Add 11.5g of dispersion accelerator 3#, which is 8% of the mass of the high-oil-content soil particles. Mix the high-oil-content soil particles with dispersion accelerator 3#. The high-oil-content soil particles gradually disperse and break into a loose state. Sieve the particles using a 2mm aperture sieve. After sieving, about 8% of the particles still have a particle size greater than 3mm. Add another 5% of the mass of dispersion accelerator 3# to this portion of the high-oil-content soil particles, mix and disperse them. After dispersion, sieve them again using a 3mm aperture sieve. At this point, all the high-oil-content soil particles are dispersed into particles with a particle size <3mm, which are called high-oil-content soil dispersed particles.

[0099] 4) Add water and cleaning agent #3 sequentially to the high-oil-content soil dispersion particles. The amount of water added is 5 times the mass of the high-oil-content soil dispersion particles, and the amount of cleaning agent #3 added is 8% of the total mass of the high-oil-content soil dispersion particles and water. Mix under a constant temperature of 60℃ to obtain mud slurry 2. The mixing is carried out using a forced electric mixer with a power of 120W. The mixing paddle is a two-blade paddle type, and the mixing paddle and blades are made of stainless steel. The mixing speed is 400r / min, and the mixing time is 30min.

[0100] 5) Add inhibitor 3# to the sieved mud to obtain mud 3. The amount of inhibitor 3# added is 10% of the mass of the sieved mud. Add inhibitor 3# and stir to mix. The stirring is done with a forced electric mixer with a motor power of 120W. The stirring paddle is a two-blade paddle type. The stirring paddle and blades are made of stainless steel. The stirring speed is 120r / min and the stirring time is 10min.

[0101] 6) After mixing mud 2 and mud 3, mud 4 is obtained. Mud 4 is then subjected to flotation treatment to obtain scum and mud 5. The flotation treatment uses a single-cell flotation machine with a motor power of 180W, an impeller diameter of 45mm, an impeller speed of 2590r / min, a scraper speed of 30r / min, and a flotation time of 40min. Petroleum contaminants in mud 4, i.e., aged crude oil, float to the surface during the air flotation process, forming scum. The scum is scraped away and collected for resource recovery. The system after removing the scum is mud 5.

[0102] 7) The mud slurry 5 was centrifuged and dewatered using a two-phase centrifuge at 3000 rpm for 10 minutes, yielding an aqueous phase and a solid phase. The aqueous phase can be collected and recycled as washing liquid. The solid phase is the treated soil with an oil content of 3.83%, weighing 144.5g after drying, with a soil loss of 44.8g. Further harmless treatment can be carried out using bioremediation, phytoremediation, or other methods.

[0103] Comparative Example 3

[0104] Step 5 is omitted; all other steps are the same as in Example 12. The soil without inhibitor treatment had an oil content of 5.01%, weighed 126.4g after drying, and suffered a soil loss of 63.7g. Compared to the soil with inhibitor, the treated soil had a higher oil content and greater soil mass loss, indicating that some soil adhered to the crude oil and floated to the surface with it during flotation.

Claims

1. An inhibitor comprising diallyl dimethyl ammonium chloride, carboxymethyl polyethylene polyamine, polyvinyl alcohol, ammonium bicarbonate, polyethylene glycol, calcium oxide, and alkali metal oxide.

2. The inhibitor according to claim 1, characterized in that, The polyvinyl alcohol has a number average molecular weight of 120,000 to 220,000; and / or the polyethylene glycol has a number average molecular weight of 1,000 to 2,000; and / or the alkali metal oxide is potassium oxide and / or sodium oxide.

3. The inhibitor according to claim 1, characterized in that, The total mass of the inhibitor is 100%, comprising 2% to 5% diallyl dimethyl ammonium chloride, 5% to 10% carboxymethyl polyethylene polyamine, 5% to 10% polyvinyl alcohol, 50% to 80% ammonium bicarbonate, 2% to 5% polyethylene glycol, 3% to 10% calcium oxide, and 3% to 10% alkali metal oxides.

4. A method for treating petroleum-contaminated soil, comprising washing and sieving the petroleum-contaminated soil to separate it into a low-oil-content fraction and a high-oil-content fraction; wherein, The low-oil-content fraction is treated with an inhibitor as described in any one of claims 1 to 3 to obtain a first-treated soil; the high-oil-content fraction is treated with a dispersant and a cleaning agent to obtain a second-treated soil; the first-treated soil and the second-treated soil are combined and subjected to flotation to separate the soil, resulting in flotation-treated soil.

5. The method according to claim 4, characterized in that, The method includes the following steps; 1) The petroleum-contaminated soil was mixed with the first washing solution to obtain mud 1; 2) The mud 1 is sieved in the second washing liquid using the first sieve to obtain mud with low oil content under the sieve and soil particles with high oil content on the sieve. 3) Dry the high oil content soil particles, add a dispersion promoter, mix and disperse, and sieve with a second sieve to obtain high oil content soil small particles smaller than the aperture of the second sieve and high oil content soil large particles larger than the aperture of the second sieve. The dispersion promoter is added to the large oil-containing soil particles larger than the aperture of the second sieve, mixed and dispersed, and then sieved using the second sieve to obtain small oil-containing soil particles smaller than the aperture of the second sieve. If there are still large oil-containing soil particles larger than the aperture of the second sieve, the dispersion promoter is added to them, mixed and dispersed, and then sieved using the second sieve until all the large oil-containing soil particles are smaller than the aperture of the second sieve after treatment, thus obtaining dispersed oil-containing soil particles. 4) The high-oil-content soil dispersion particles are mixed with the third washing solution and cleaning agent to obtain mud slurry 2; 5) Mix the screened mud with the inhibitor to obtain mud 3; 6) Mix the mud 2 and the mud 3 to obtain mud 4; subject the mud 4 to flotation treatment to obtain scum and mud 5, wherein the scum is removed from the mud 5; 7) The mud 5 is subjected to solid-liquid separation, wherein the solid phase is the treated soil.

6. The method according to claim 5, characterized in that, In step 1), the mass ratio of the petroleum-contaminated soil to water is 1:(1 to 3), and the mixture is soaked for 2 to 4 hours to obtain the mud 1.

7. The method according to claim 5, characterized in that, The aperture of the first and second sample sieves is 1 to 3 mm.

8. The method according to claim 5, characterized in that, The temperature of the second washing solution is 50 to 70°C; and / or The temperature at which the mud slurry 2 is prepared is 50 to 60°C.

9. The method according to claim 5, characterized in that, Place the first sieve above the surface of the second washing liquid, pour the mud 1 into the first sieve, cover the first sieve with the sieve cover, and fix the first sieve and the sieve cover. Submerge the first sieve in the second washing liquid, then lift it up. Repeat this process 10 to 20 times to obtain the low oil content mud slurry and the high oil content soil particles on the sieve after sieving.

10. The method according to claim 5, characterized in that, Based on the mass of the high-oil-content soil particles (100%), the initial addition amount of the dispersion accelerator is 3% to 8%, wherein the moisture content of the high-oil-content soil particles is 13% to 18%; and / or Based on the mass of the large particles in the high-oil-content soil as 100%, the subsequent addition of the dispersion accelerator is 1% to 5%; and / or The mass ratio of the high-oil-content soil dispersion particles to the third washing solution is 1:(2 to 5); and / or The cleaning agent is used in an amount of 3% to 8%, calculated as 100% of the total mass of the high-oil-content soil dispersion particles and the third washing solution; and / or The amount of the inhibitor used is 5% to 10%, calculated as 100% by mass of the screened slurry.