Remediation agents, their use and methods for remediating cyanide-organic compound composite contaminated sites

Abstract

The present application relates to the field of cyanide-organic compound composite contaminated site remediation, and discloses a kind of remediation agent and its application and the method for treating cyanide-organic compound composite contaminated site.A kind of remediation agent, the remediation agent includes: iron-carbon composite material, guar gum solution, persulfate, sodium percarbonate and calcium carbide slag.The remediation agent can effectively solve the problem that single remediation agent is difficult to repair cyanide-organic compound composite pollution to reach the standard, while solving the problem of excessive use of persulfate, excessive sulfate ions and serious corrosion.

Description

Technical Field

[0001] This invention relates to the field of remediation of sites contaminated with cyanide-organic compounds, specifically to a remediation agent, its application, and a method for treating sites contaminated with cyanide-organic compounds. Background Technology

[0002] As industrial enterprises in old urban areas are relocated to industrial parks, suburbs, or development zones to coordinate urban land use structure, some heavily polluting enterprises have left behind a large number of polluted sites after ceasing production or relocating, becoming potential sources of pollution with extremely high environmental risks.

[0003] Cyanide is widely used in industrial production, and therefore it is commonly found in the soil and groundwater of contaminated sites in industries such as chemical fiber, electroplating, metallurgy, coking, leather making, dyeing, and rubber. It often forms complex pollution with organic compounds such as benzene series compounds, polycyclic aromatic hydrocarbons, and petroleum hydrocarbons.

[0004] For sites contaminated with cyanide and organic matter, commonly used remediation technologies include cement kiln co-processing, electrodynamic remediation, leaching, microbial remediation, and chemical oxidation. Among these, chemical oxidation technology is increasingly being researched and applied both domestically and internationally due to its large processing capacity, high efficiency, and relatively low cost. For example, CN107138519A discloses an ex-situ chemical oxidation remediation method for cyanide-contaminated soil, using activated persulfate and hydrogen peroxide to remove cyanide from the soil. CN101417287A discloses a chemical remediation method for cyanide-contaminated soil, using chlorine dioxide disinfectant as an oxidant to treat cyanide-containing soil. CN111408612A provides an engineering remediation method for cyanide-contaminated soil, combining soil oxidation and soil leaching technologies to treat moderately to severely cyanide-contaminated soil.

[0005] Analysis of existing technologies reveals that commonly used oxidizing agents for remediating cyanide-organic compound contaminated sites, both domestically and internationally, include hydrogen peroxide, Fenton's reagent, persulfate, and permanganate. Commonly used remediation processes include ex-situ chemical oxidation, in-situ injection, groundwater extraction and treatment, ex-situ leaching, and mud reactors.

[0006] However, existing technologies still have many shortcomings, such as:

[0007] Regarding remediation agents, Fenton-type agents with hydrogen peroxide as the core generally suffer from problems such as short duration of effect and easy soil acidification; permanganate is difficult for the public to accept due to its color and has relatively limited selectivity for pollutants; although persulfate is the most commonly used, its single oxidation system has a certain selectivity for pollutants, making it difficult to achieve the remediation standards for cyanide-organic compound pollution. Furthermore, previous studies and applications have often overlooked the problem of sulfate exceeding the standard due to excessive use of persulfate. The corrosiveness caused by excessive sulfate seriously affects the subsequent development and utilization of the site.

[0008] In terms of remediation technology, since most contaminated sites involve both soil and groundwater pollution, traditional ex-situ remediation technologies such as ex-situ chemical oxidation and groundwater extraction cannot achieve comprehensive water and soil remediation, resulting in increased remediation costs. Existing in-situ remediation technologies are mostly implemented through well injection, high-pressure jet injection, and direct-push injection, which have high requirements for the hydrogeological conditions of the site. Especially for low-permeability soils such as clay, it is difficult to achieve effective mass transfer, resulting in waste of remediation agents and reduced remediation efficiency. Summary of the Invention

[0009] The purpose of this invention is to overcome the problems existing in the prior art and provide a remediation agent, its application, and a method for treating sites contaminated with cyanide-organic compounds. This remediation agent can effectively solve the problem that a single remediation agent is insufficient to remediate cyanide-organic compound contamination to the required standards, while also addressing the problems of excessive sulfate ions and severe corrosiveness caused by the overuse of persulfate.

[0010] To achieve the above objectives, the present invention provides a repair agent comprising: an iron-carbon composite material, a guar gum solution, persulfate, sodium percarbonate, and carbide slag.

[0011] The second aspect of this invention provides the application of the remediation agent described in the first aspect in the treatment of sites contaminated with cyanide-organic compounds.

[0012] A third aspect of the present invention provides a method for treating sites contaminated with cyanide-organic compounds, the method comprising:

[0013] (1) In the area to be repaired, a mixture of iron-carbon composite material and guar gum solution is subjected to hydraulic fracturing until a crack network is generated;

[0014] (2) Inject the persulfate solution into the area to be repaired, and then perform the first curing;

[0015] (3) Inject sodium percarbonate aqueous solution into the area to be repaired, and then carry out the second curing;

[0016] (4) The above-mentioned areas to be repaired are stirred in situ, and carbide slag suspension is injected at the same time, and then the third curing is carried out.

[0017] The beneficial effects of the present invention through the above technical solution include:

[0018] This invention provides a remediation agent that utilizes iron-carbon composite materials, guar gum solution, persulfate, sodium percarbonate, and carbide slag to achieve synergistic effects, broadening the oxidative selectivity for pollutants and enhancing the oxidation capacity of the oxidation system. It solves the problem that a single remediation agent is insufficient to remediate cyanide-organic compound pollution to the required standards, improves agent utilization efficiency, and reduces remediation costs. Furthermore, it addresses the issues of excessive persulfate use in traditional remediation technologies, which leads to excessive sulfate ions and severe corrosiveness, and is of great significance for the subsequent development and utilization of the site.

[0019] This invention provides a method for remediating sites contaminated with cyanide and organic matter. This method is widely applicable to contaminated sites of various soil types, and in particular solves the problem of effective mass transfer in low-permeability soils such as clay. It achieves comprehensive remediation of cyanide, organic matter, and sulfate, eliminates secondary pollution during the remediation process, ensures that various indicators of soil and groundwater tend to stabilize, eliminates long-term environmental risks to the site, and realizes comprehensive remediation of sites contaminated with cyanide and organic matter.

[0020] The remediation agent and method provided by this invention also realize the comprehensive utilization of carbide slag. The small amount of pollutants such as sulfides and organic matter that may be contained in carbide slag are completely removed by the method described in this invention, truly realizing the harmless and resource-based utilization of carbide slag and turning waste into treasure. Attached Figure Description

[0021] Figure 1 This is a flowchart of the method for treating sites contaminated with cyanide-organic compounds as described in this invention.

[0022] Explanation of reference numerals in the attached figures

[0023] Agent A: Iron-carbon composite material; Agent B: Guar gum solution; Agent C: Persulfate;

[0024] Agent D: Sodium percarbonate; Agent E: Carbide slag suspension. Detailed Implementation

[0025] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0026] One aspect of this invention provides a repair agent comprising: an iron-carbon composite material, guar gum solution, persulfate, sodium percarbonate, and carbide slag.

[0027] According to the present invention, preferably, the iron-carbon composite material comprises an iron component, a carbon component, and a sand component; the volume ratio of iron component:carbon component:sand component is 1:1-3:1-5, preferably 1:1-1.5:1-3. Using this preferred embodiment, synergistic effects with other substances can effectively improve the repair effect.

[0028] According to the present invention, preferably, the iron component is nano-zero valent iron and / or micro-zero valent iron. All of the above substances are commercially available.

[0029] According to the present invention, preferably, the carbon component is activated carbon.

[0030] The activated carbon described in this invention can be obtained in various forms and by various production methods, and this invention does not limit it.

[0031] According to the present invention, preferably, the particle size of the carbon component is not less than 50 mesh, and more preferably 50-325 mesh. Using this preferred embodiment, in subsequent applications to the remediation of cyanide-organic compound contaminated sites, it can be ensured that the iron-carbon composite material is injected into the area to be remediated in a fluid manner.

[0032] The present invention allows for a wide range of selection of sand components, which can be various types of sand and gravel commonly used in the field.

[0033] According to the present invention, preferably, the particle size of the sand component is not higher than 1 mm, and more preferably 0.05-1 mm. Using this preferred embodiment, in subsequent applications to the remediation of cyanide-organic compound contaminated sites, it can be ensured that the iron-carbon composite material is injected into the area to be remediated in a fluid manner.

[0034] Guar gum, as the most viscous natural gum, exhibits remarkable repair effects when combined with other substances. According to the present invention, preferably, the concentration of the guar gum solution is 0.05-2 wt%, more preferably 0.1-1 wt%.

[0035] According to the present invention, preferably, the solvent of the guar gum solution is water. This preferred embodiment introduces no organic matter and is economical and cost-effective.

[0036] This invention allows for a wide range of persulfates, which can be conventional choices in the field. Preferably, the persulfate is sodium persulfate and / or potassium persulfate. All of these substances are commercially available.

[0037] The calcium carbide slag described in this invention, on the one hand, together with iron-carbon composite material, guar gum solution, persulfate, and sodium percarbonate, constitutes a multi-stage oxidizing agent system; on the other hand, it reacts with excess sulfate ions to generate calcium sulfate precipitate, thereby eliminating secondary sulfate pollution caused by the addition of oxidizing agents.

[0038] According to the present invention, preferably, the content of calcium hydroxide is not less than 70% by weight, and more preferably not less than 80% by weight, based on the total weight of the carbide slag.

[0039] In this invention, the carbide slag contains calcium hydroxide and small amounts of impurities such as sulfides and organic matter. During the research process, the inventors discovered that the carbide slag, when used in combination with iron-carbon composite materials, guar gum solution, persulfate, and sodium percarbonate, exhibits significant remediation effects in treating sites contaminated with cyanide and organic matter. Furthermore, during this process, impurities such as sulfides and organic matter in the carbide slag are completely removed, achieving the harmless and resource-based utilization of the carbide slag, turning waste into treasure.

[0040] According to the present invention, as long as the above requirements are met, calcium carbide slag produced by various processes well known to those skilled in the art can be used. Preferably, the calcium carbide slag is the waste residue from the hydrolysis of calcium carbide to produce acetylene gas.

[0041] According to the present invention, preferably, the weight ratio of iron-carbon composite material to persulfate is 0.5-10:1-30, more preferably 1-5:3-15, wherein the iron-carbon composite material is based on iron content.

[0042] According to the present invention, preferably, the weight ratio of persulfate to sodium percarbonate is 1-30:1-20, more preferably 3-15:2-10.

[0043] According to the present invention, preferably, the weight ratio of persulfate to carbide slag is 1-30:1-20, more preferably 3-15:2-10, wherein the carbide slag is based on the weight of calcium hydroxide.

[0044] Preferably, the volume ratio of the guar gum solution to the iron-carbon composite material is 1-15:1, more preferably 2-8:1, wherein the iron-carbon composite material is calculated based on the iron component. The content of each component in this invention is within the above range, which can sufficiently ensure the repair effect of the pharmaceutical system.

[0045] The second aspect of this invention provides the application of the remediation agent described in the first aspect in the treatment of sites contaminated with cyanide-organic compounds.

[0046] A third aspect of the present invention provides a method for treating sites contaminated with cyanide-organic compounds, the method comprising:

[0047] (1) In the area to be repaired, a mixture of iron-carbon composite material and guar gum solution is subjected to hydraulic fracturing until a crack network is generated;

[0048] (2) Inject the persulfate solution into the area to be repaired, and then perform the first curing;

[0049] (3) Inject sodium percarbonate aqueous solution into the area to be repaired, and then carry out the second curing;

[0050] (4) The above-mentioned areas to be repaired are stirred in situ, and carbide slag suspension is injected at the same time, and then the third curing is carried out.

[0051] This invention provides an in-situ remediation method that includes hydraulic fracturing, two-stage in-situ injection, and in-situ deep stirring. Combined with remediation agents of specific components, it achieves comprehensive remediation of cyanide, organic matter, and sulfate, eliminates secondary pollution during the remediation process, ensures that various indicators of soil and groundwater tend to stabilize, eliminates long-term environmental risks to the site, and realizes comprehensive treatment of sites contaminated with cyanide-organic compounds.

[0052] In this invention, after hydraulic fracturing as described in step (1), the iron-carbon composite material and guar gum solution fill the crack network, which significantly increases the permeability of the soil within the contaminated area, effectively improves the mass transfer capacity of each component of the agent in the soil and groundwater in the subsequent remediation steps, shortens the mass transfer path, increases the contact efficiency between the agent and the pollutants, and effectively improves the remediation effect.

[0053] In this invention, the area to be remediated refers to a site contaminated with a combination of cyanide and organic matter.

[0054] This invention does not particularly limit the method for injecting the components of the repair agent into the area to be repaired; methods commonly used in the art can be employed. For example, injection wells can be installed or a direct-drive drilling rig can be used for injection; this invention does not limit the method.

[0055] The present invention has a wide range of pressure selection for hydraulic fracturing. Preferably, the hydraulic fracturing pressure in step (1) is 0.3-5 MPa, and more preferably 0.5-3 MPa.

[0056] The iron-carbon composite material described in this invention serves as a proppant for hydraulic fracturing on one hand, and together with other substances, constitutes a multi-stage oxidizing agent system on the other.

[0057] According to the present invention, preferably, the amount of the iron-carbon composite material is 0.05-1% of the mass of the contaminated soil and groundwater to be remediated, more preferably 0.1-0.5%, wherein the iron-carbon composite material is calculated as iron component.

[0058] According to the present invention, preferably, the volume ratio of guar gum solution to iron-carbon composite material is 1-15:1, more preferably 2-8:1, wherein the iron-carbon composite material is calculated as iron component.

[0059] According to the present invention, preferably, the iron-carbon composite material includes an iron component, a carbon component and a sand component; the volume ratio of iron component: carbon component: sand component is 1:1-3:1-5, preferably 1:1-1.5:1-3.

[0060] According to the present invention, preferably, the iron component is nano-zero valent iron and / or micro-zero valent iron. All of the above substances are commercially available.

[0061] According to the present invention, preferably, the carbon component is activated carbon. The activated carbon described in the present invention can be obtained in various forms and by various production methods, and the present invention does not limit its use.

[0062] According to the present invention, preferably, the particle size of the carbon component is not less than 50 mesh, and more preferably 50-325 mesh.

[0063] The present invention allows for a wide range of selection of sand components, which can be various types of sand and gravel commonly used in the field.

[0064] According to the present invention, preferably, the particle size of the sand component is not higher than 1 mm, and more preferably 0.05-1 mm.

[0065] According to the present invention, preferably, the concentration of the guar gum solution is 0.05-2 wt%, more preferably 0.1-1 wt%.

[0066] According to the present invention, preferably, the solvent of the guar gum solution is water. This preferred embodiment introduces no organic matter and is economical and cost-effective.

[0067] In step (2) of this invention, after persulfate is injected into the area to be repaired, the iron-carbon composite material therein stimulates the persulfate to generate sulfate free radicals, and performs preliminary oxidative remediation of the cyanide-organic compound contaminated site within the first curing time.

[0068] According to the present invention, preferably, the amount of persulfate used is 0.1-3% of the mass of the contaminated soil and groundwater to be remediated, more preferably 0.3-1.5%. This amount is lower than the conventional amount used in techniques that use persulfate alone as an oxidant, thereby reducing the sulfate ion content introduced by the addition of the agent.

[0069] According to the present invention, preferably, the concentration of the persulfate aqueous solution is 5-40 wt%, more preferably 10-30 wt%.

[0070] According to the present invention, preferably, the persulfate is sodium persulfate and / or potassium persulfate.

[0071] According to the present invention, preferably, the first curing time is 0.5-4 days, more preferably 1-2 days. This preferred embodiment ensures that the persulfate, after injection, fully reacts with other substances in the fracture network generated by hydraulic fracturing, thus performing preliminary oxidative remediation of cyanide-organic compound contaminated sites.

[0072] In step (3) of this invention, after sodium percarbonate is injected into the area to be remediated, it stimulates the unconsumed persulfate on the one hand, and works synergistically with other substances to generate sulfate free radicals and hydroxyl free radicals, further oxidizing and remediating the cyanide-organic compound contaminated site during the second curing period. After step (3), the soil moisture content increases significantly, which is beneficial for the implementation of the next step of in-situ deep and powerful mixing.

[0073] The synergistic effect among the added reagent components broadens the selectivity for pollutant oxidation, enhances the oxidation capacity of the oxidation system, and achieves phased activation and oxidation through staged injection, thus extending the duration of the oxidation effect.

[0074] According to the present invention, preferably, the amount of sodium percarbonate used is 0.1-2% of the mass of the contaminated soil and groundwater to be remediated, and more preferably 0.2-1%.

[0075] According to the present invention, preferably, the concentration of the sodium percarbonate aqueous solution is 5-30 wt%, more preferably 10-20 wt%.

[0076] According to the present invention, preferably, the second curing time is 1-5 days, more preferably 2-3 days. This preferred embodiment ensures that the added agents fully exert their synergistic effect, further oxidizing and remediating cyanide-organic compound pollution.

[0077] In step (4) of this invention, after the calcium carbide slag suspension is injected, the pH of the soil and groundwater environment rises to about 9-11. On the one hand, this stimulates the unconsumed persulfate and sodium percarbonate, generating sulfate free radicals, hydroxyl free radicals, and superoxide free radicals, which thoroughly remediate the cyanide-organic compound contaminated site during the third curing period. On the other hand, it reacts with excess sulfate in the soil and groundwater to generate calcium sulfate precipitate, eliminating secondary sulfate pollution caused by the addition of oxidizing agents. At the same time, in-situ deep stirring can further mix the remediation agent with the contaminated soil and groundwater evenly, further improving the agent utilization efficiency. In addition, the small amount of sulfides, organic matter, and other pollutants contained in the calcium carbide slag are completely removed, truly realizing the harmless and resource-based utilization of the calcium carbide slag, turning waste into treasure.

[0078] The present invention does not impose any particular limitation on the stirring speed and time, which can be appropriately selected according to the specific circumstances, so as to achieve the purpose of uniformly mixing the remediation agent with the contaminated soil and groundwater.

[0079] According to the present invention, preferably, the amount of the carbide slag suspension is 0.1-2% of the mass of the contaminated soil and groundwater to be remediated, more preferably 0.2-1%, wherein the carbide slag suspension is based on the weight of calcium hydroxide in the carbide slag.

[0080] According to the present invention, preferably, the concentration of the carbide slag suspension is 3-30 wt%, more preferably 5-20 wt%.

[0081] According to the present invention, preferably, the solvent for the calcium carbide slag suspension is water. This preferred embodiment introduces no organic matter, is economical, and saves costs.

[0082] According to the present invention, preferably, the content of calcium hydroxide is not less than 70% by weight, and more preferably not less than 80% by weight, based on the total weight of the carbide slag.

[0083] According to the present invention, preferably, the calcium carbide slag is the waste residue from the hydrolysis of calcium carbide to prepare acetylene gas.

[0084] According to the present invention, preferably, the third maintenance period is 3-15 days, more preferably 5-7 days.

[0085] Preferably, the method further includes monitoring the area to be repaired after the third curing step is completed. This preferred implementation method allows for the timely detection of rebound effects that are prone to occur with chemical oxidation techniques, enabling timely remedial measures to truly eliminate long-term environmental risks to the site and ultimately achieve comprehensive and harmless remediation of the site.

[0086] Preferably, the monitoring period is no less than one year.

[0087] Preferably, the monitoring includes groundwater monitoring, soil monitoring, trend analysis, and recharge.

[0088] The groundwater monitoring includes: setting up monitoring wells upstream, downstream, at the boundary and inside of the above-mentioned remediated area, taking samples regularly for testing, with a sampling frequency of no less than once per quarter, and testing indicators including pollutant concentration, sulfate content, pH, redox potential, conductivity, dissolved oxygen, total hardness, water level, etc.

[0089] The soil monitoring includes: taking regular samples and testing in the remediated area, with a sampling frequency of no less than once every six months and a monitoring period of no less than one year. The testing indicators include pollutant concentration, sulfate content, and pH.

[0090] The trend analysis and replenishment include: analyzing the monitoring data of the soil and groundwater, paying attention to the changing trends of each indicator; if the pollutant concentration rebounds above the remediation target, sodium percarbonate will be replenished at the exceeding points and the monitoring time will be extended accordingly; if the pollutants continue to meet the standards and other indicators remain generally stable, the remediation will end.

[0091] The present invention does not impose any particular limitation on the amount of sodium percarbonate to be added, and can be selected appropriately according to specific circumstances.

[0092] This invention does not impose any particular limitation on the method of sodium percarbonate injection; methods commonly used in the art can be employed. Preferably, this invention uses a direct-drive drilling rig for injection.

[0093] According to the present invention, preferably, the method further includes: step (1) before hydraulic fracturing the mixture of iron-carbon composite material and guar gum solution, drilling is performed to the depth to be repaired.

[0094] The depth to be repaired in this invention is the contamination depth. This contamination depth is provided to the customer.

[0095] The method for determining the borehole location described in this invention is not particularly limited and can be determined using commonly used techniques in the field. This invention first determines the radius of influence of hydraulic fracturing based on the site's hydrogeological conditions, and then determines the specific location of the borehole within the area to be repaired. The radius of influence of hydraulic fracturing is generally 5-15m.

[0096] According to the present invention, preferably, the method further includes: after drilling is completed, water is injected until the core region of the forming disc is formed.

[0097] The present invention allows for a wide range of water pressure options. Preferably, the water pressure is 20-30 MPa.

[0098] The method described in this invention is applicable to sites with combined cyanide-organic contamination at various concentrations. Since the contamination characteristics of different sites vary greatly, the method can be applied to sites with different pollutant concentrations by adjusting the dosage of the reagent and the method parameters. For sites with particularly severe contamination, the technical steps of this solution can be repeated multiple times.

[0099] According to the present invention, preferably, in a site contaminated with a combination of cyanide and organic matter, the cyanide includes organic cyanide and / or inorganic cyanide, preferably inorganic cyanide.

[0100] The organic compounds include at least one of benzene compounds, polycyclic aromatic hydrocarbons, and petroleum hydrocarbons.

[0101] In this invention, the terms "first," "second," and "third" do not limit the substances and operations, but are only used to distinguish the substances introduced in different steps and the operations performed in different stages.

[0102] The present invention will be described in detail below through embodiments.

[0103] The reagents used in the following examples are commercially available and of analytical grade.

[0104] Example 1

[0105] Comprehensive remediation project of a chemical fiber contaminated site in Shandong

[0106] This project is a site contaminated with synthetic fibers. The main pollutants in the soil include: inorganic cyanide 293 mg / kg, benzo(a)pyrene 4.3 mg / kg, benzo(a)anthracene 6.5 mg / kg, benzo(b)fluoranthracene 6.8 mg / kg, and dibenzo(a,h)anthracene 3.8 mg / kg. Cyanide levels in the groundwater exceed the standard. The site is subsequently planned for Class I construction land use. The soil within the contamination depth range is mainly silty clay with a permeability coefficient of 10. -5 ~10 -6 On the order of cm / s.

[0107] The comprehensive remediation of the site using the remediation agents and methods provided by this invention specifically includes:

[0108] (1) Composition of the repair agent:

[0109] Agent A: Micron-sized zero-valent iron, 100-mesh activated carbon, and 0.5mm sand and gravel, with a volume ratio of iron:carbon:sand (V:V:V)=1:1:1;

[0110] Agent B: 0.5 wt% guar gum aqueous solution;

[0111] Agent C: Potassium persulfate;

[0112] Agent D: Sodium percarbonate;

[0113] Agent E: 10wt% calcium carbide slag suspension, with calcium hydroxide content of 83.5wt% in the calcium carbide slag.

[0114] (2) Restoration and remediation process:

[0115] The following is in conjunction with the appendix Figure 1 The method described in this invention will be explained in detail.

[0116] 1) Hydraulic fracturing: Based on the site's hydrogeological conditions, the influence radius of hydraulic fracturing was determined to be 10m. The borehole location was determined, and drilling was carried out to the depth to be remediated. High-pressure water of approximately 20MPa was injected to form a core zone. A mixed solution of agent A and agent B was used for hydraulic fracturing at a pressure of 1.2MPa, employing an intermittent fracturing method until a fracture network was generated. Based on the quality of the contaminated soil and groundwater to be remediated, the dosage of agent A was 0.2%, and the dosage of agent B was 0.8%.

[0117] 2) First-stage in-situ injection: Prepare a 15wt% solution of Agent C and inject it into the hydraulic fracturing borehole. The dosage of Agent C is 0.6% based on the quality of the contaminated soil and groundwater to be remediated. After injection, allow it to cure for 1 day.

[0118] 3) Second-stage in-situ injection: Prepare agent D into a 15wt% solution and inject it into the hydraulic fracturing borehole. The dosage of agent D is 0.4% based on the quality of the contaminated soil and groundwater to be remediated. After injection, cure for 2 days.

[0119] 4) In-situ deep mixing: In-situ deep mixing was carried out in the above-mentioned area to be remediated, and agent E was injected at the same time. The dosage of agent E was 0.4% based on the quality of the contaminated soil and groundwater to be remediated. After testing, the pH of the soil and groundwater environment increased to about 10.1 after the injection of agent E. After the injection was completed, the soil and groundwater environment was cured for 6 days.

[0120] 5) Long-term monitoring: Groundwater monitoring wells will be installed upstream, downstream, at the boundary and inside the remediated area. Sampling and testing will be conducted regularly, once per quarter, for a period of one year. The test indicators include pollutant concentration, sulfate content, pH, redox potential, conductivity, dissolved oxygen, total hardness and water level. Soil samples will also be taken regularly within the remediated area, once every six months, for a period of one year. The test indicators include pollutant concentration, sulfate content and pH.

[0121] Data analysis showed that during the long-term monitoring period, the concentrations of pollutants in the soil and groundwater all decreased to below the detection limits of the detection methods specified in GB36600-2018 standard. All pollutants were remediated to the required standards without any rebound. The sulfate content remained within the weak corrosion standard range specified in the Code for Geotechnical Engineering Investigation (GB50021-2001). The pH value dropped to the range of 6 to 9. Other indicators generally tended to be stable, and the comprehensive site remediation was successfully completed.

[0122] Example 2

[0123] Comprehensive remediation project of a coking site in Jiangsu

[0124] This project is a site contaminated with synthetic fibers. The main pollutants in the soil include: inorganic cyanide 458 mg / kg, benzo(a)pyrene 3.5 mg / kg, benzo(a)anthracene 5.8 mg / kg, benzo(b)fluoranthracene 4.2 mg / kg, dibenzo(a,h)anthracene 2.7 mg / kg, indo(1,2,3-cd)pyrene 2.3 mg / kg, xylene 23 mg / kg, and total petroleum hydrocarbons 1538 mg / kg. Cyanide and total petroleum hydrocarbons in the groundwater exceed the standards. The site is subsequently planned for Class I construction land use. The soil within the contamination depth range is mainly silty clay and clay, with a permeability coefficient of 10. -5 ~10 -7 On the order of cm / s.

[0125] The comprehensive remediation of the site using the remediation agents and methods provided by this invention specifically includes:

[0126] (1) Pharmaceutical composition:

[0127] Agent A: Nano-zero valent iron, 200-mesh activated carbon, and 0.8mm sand. The volume ratio of each component is iron:carbon:sand (V:V:V)=1:1:3.

[0128] Agent B: 1 wt% guar gum solution;

[0129] Agent C: Sodium persulfate;

[0130] Agent D: Sodium percarbonate;

[0131] Agent E: 20wt% calcium carbide slag suspension, with calcium hydroxide content in the calcium carbide slag being 85wt%;

[0132] (2) Restoration and remediation process:

[0133] 1) Hydraulic fracturing: Based on the site's hydrogeological conditions, the influence radius of hydraulic fracturing was determined to be 7m. The borehole location was determined, and drilling was carried out to the depth to be remediated. High-pressure water at approximately 25MPa was injected to form a core area. A mixed solution of agent A and agent B was then used for hydraulic fracturing at a pressure of 2.2MPa, employing an intermittent fracturing method until a fracture network was generated. Based on the quality of the contaminated soil and groundwater to be remediated, the dosage of agent A was 0.4%, and the dosage of agent B was 1.2%.

[0134] 2) First-stage in-situ injection: Prepare a 25wt% solution of Agent C and inject it into the hydraulic fracturing borehole. The dosage of Agent C is 1.2% based on the quality of the contaminated soil and groundwater to be remediated. After injection, allow it to cure for 2 days.

[0135] 3) Second-stage in-situ injection: Prepare agent D into a 20wt% solution and inject it into the hydraulic fracturing borehole. The dosage of agent D is 0.8% based on the quality of the contaminated soil and groundwater to be remediated. After injection, cure for 3 days.

[0136] 4) In-situ deep mixing: In-situ deep mixing was carried out on the above-mentioned areas to be remediated, and E agent was injected at the same time. The dosage of E agent was 0.8% based on the quality of the contaminated soil and groundwater to be remediated. After testing, the pH of the soil and groundwater environment increased to about 10.8 after the injection of E agent. After the injection was completed, the soil and groundwater environment was cured for 7 days.

[0137] 5) Long-term monitoring: Groundwater monitoring wells will be installed upstream, downstream, at the boundary and inside the remediated area. Sampling and testing will be conducted regularly, twice a quarter, for a period of one year. The test indicators include pollutant concentration, sulfate content, pH, redox potential, conductivity, dissolved oxygen, total hardness and water level. Soil samples will also be taken regularly within the remediated area, once a quarter, for a period of one year. The test indicators include pollutant concentration, sulfate content and pH.

[0138] Data analysis revealed that, during the long-term monitoring period, the total petroleum hydrocarbons at one monitoring point slightly exceeded the standard in one test due to water level changes during the wet and dry seasons. The exceedance was 0.2 times the standard. Agent D was injected directly into the point and its surrounding area using a direct injection method, and the long-term monitoring period was extended by 1 year, for a total long-term monitoring period of 1 year and 6 months.

[0139] During the one-year long-term monitoring period following the refilling, the concentrations of cyanide, polycyclic aromatic hydrocarbons, and xylene in the soil and groundwater all decreased to below the detection limits specified in the GB36600-2018 standard, the total petroleum hydrocarbon concentration decreased to below 180 mg / kg, all pollutants were remediated to meet the standards and there was no rebound, the sulfate content remained within the weak corrosion standard range specified in the "Code for Geotechnical Engineering Investigation" (GB50021-2001), the pH dropped to the range of 6-9, and other indicators generally tended to be stable, and the comprehensive site remediation was successfully completed.

[0140] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for treating a site contaminated with cyanide-organic compounds, the method comprising: (1) In the area to be repaired, a mixture of iron-carbon composite material and guar gum solution is subjected to hydraulic fracturing until a crack network is generated; The iron-carbon composite material comprises an iron component, a carbon component, and a sand component; the volume ratio of the iron component to the carbon component to the sand component is 1:1-3:1-5. (2) Inject the persulfate solution into the area to be repaired, and then perform the first curing; (3) Inject sodium percarbonate aqueous solution into the area to be repaired, and then carry out the second curing; (4) The above-mentioned area to be repaired is stirred in situ, and carbide slag suspension is injected at the same time. The pH is raised to 9-11, and then the third curing is carried out. The amount of the iron-carbon composite material used is 0.05-1% of the mass of the contaminated soil and groundwater to be remediated, wherein the iron-carbon composite material is calculated as iron component; The amount of persulfate used is 0.1-3% of the mass of the contaminated soil and groundwater to be remediated; The amount of sodium percarbonate used is 0.1-2% of the mass of the contaminated soil and groundwater to be remediated; The amount of the calcium carbide slag suspension used is 0.1-2% of the mass of the contaminated soil and groundwater to be remediated, wherein the calcium carbide slag suspension is calculated by weight of calcium hydroxide in the calcium carbide slag. The method also includes: monitoring the above-mentioned area to be repaired after the third maintenance is completed; the monitoring period is not less than 1 year; wherein the pH of the remediated contaminated site drops to the range of 6-9.

2. The method according to claim 1, wherein, The hydraulic fracturing pressure in step (1) is 0.3-5 MPa.

3. The method according to claim 2, wherein, The hydraulic fracturing pressure in step (1) is 0.5-3 MPa.

4. The method according to claim 1, wherein, The amount of the iron-carbon composite material used is 0.1-0.5% of the mass of the contaminated soil and groundwater to be remediated, wherein the iron-carbon composite material is calculated as iron component.

5. The method according to claim 1, wherein, The volume ratio of guar gum solution to iron-carbon composite material is 1-15:1, wherein the iron-carbon composite material is calculated based on the iron component.

6. The method according to claim 5, wherein, The volume ratio of guar gum solution to iron-carbon composite material is 2-8:1, wherein the iron-carbon composite material is calculated based on the iron component.

7. The method according to claim 1, wherein, In the iron-carbon composite material, the volume ratio of iron component: carbon component: sand component is 1:1-1.5:1-3.

8. The method according to claim 1, wherein, The iron component is nano-zero valent iron and / or micro-zero valent iron.

9. The method according to claim 1, wherein, The carbon component is activated carbon.

10. The method according to claim 1, wherein, The particle size of the carbon component is not less than 50 mesh.

11. The method according to claim 10, wherein, The particle size of the carbon component is 50-325 mesh.

12. The method according to claim 1, wherein, The particle size of the sand component is no higher than 1 mm.

13. The method according to claim 12, wherein, The particle size of the sand component is 0.05-1 mm.

14. The method according to claim 1, wherein, The concentration of the guar gum solution is 0.05-2 wt%.

15. The method according to claim 14, wherein, The concentration of the guar gum solution is 0.1-1 wt%.

16. The method according to claim 1, wherein, The solvent for the guar gum solution is water.

17. The method according to claim 1, wherein, The amount of persulfate used is 0.3-1.5% of the mass of the contaminated soil and groundwater to be remediated.

18. The method according to claim 1, wherein, The concentration of the persulfate aqueous solution is 5-40 wt%.

19. The method according to claim 18, wherein, The concentration of the persulfate aqueous solution is 10-30 wt%.

20. The method according to claim 1, wherein, The persulfate is sodium persulfate and / or potassium persulfate.

21. The method according to claim 1, wherein, The first curing period is 0.5-4 days.

22. The method according to claim 21, wherein, The first maintenance period is 1-2 days.

23. The method according to claim 1, wherein, The amount of sodium percarbonate used is 0.2-1% of the mass of the contaminated soil and groundwater to be remediated.

24. The method according to claim 1, wherein, The concentration of the sodium percarbonate aqueous solution is 5-30 wt%.

25. The method according to claim 24, wherein, The concentration of the sodium percarbonate aqueous solution is 10-20 wt%.

26. The method according to claim 1, wherein, The second maintenance period is 1-5 days.

27. The method according to claim 26, wherein, The second maintenance period is 2-3 days.

28. The method according to claim 1, wherein, The amount of the carbide slag suspension used is 0.2-1% of the mass of the contaminated soil and groundwater to be remediated, wherein the carbide slag suspension is calculated by weight of calcium hydroxide in the carbide slag.

29. The method according to any one of claims 1-28, wherein, The concentration of the carbide slag suspension is 3-30 wt%.

30. The method according to claim 29, wherein, The concentration of the carbide slag suspension is 5-20 wt%.

31. The method according to any one of claims 1-28, wherein, The solvent for the calcium carbide slag suspension is water.

32. The method according to any one of claims 1-28, wherein, Based on the total weight of the carbide slag, the content of calcium hydroxide shall not be less than 70% by weight.

33. The method according to claim 32, wherein, Based on the total weight of the carbide slag, the content of calcium hydroxide shall not be less than 80% by weight.

34. The method according to any one of claims 1-28, wherein, The calcium carbide slag is the waste residue from the hydrolysis of calcium carbide to produce acetylene gas.

35. The method according to any one of claims 1-28, wherein, The third maintenance period is 3-15 days.

36. The method according to claim 35, wherein, The third maintenance period is 5-7 days.

37. The method according to claim 1, wherein, The monitoring includes groundwater monitoring, soil monitoring, trend analysis, and recharge.

38. The method according to any one of claims 1-28, wherein, In sites contaminated with a combination of cyanide and organic pollutants, the cyanide includes organic cyanide and / or inorganic cyanide; The organic compounds include at least one of benzene compounds, polycyclic aromatic hydrocarbons, and petroleum hydrocarbons.

39. The method according to any one of claims 1-28, wherein, The method also includes: step (1) before hydraulic fracturing the mixture of iron-carbon composite material and guar gum solution, drilling is performed to the depth to be repaired.

40. The method according to claim 39, wherein, The method also includes: after drilling is completed, water is injected until the core area of ​​the forming disc is formed.

41. The method according to claim 40, wherein, The water pressure is 20-30 MPa.

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