Remediation agent and remediation method for hexavalent chromium contaminated soil

Abstract

The invention provides a remediation agent and a remediation method for hexavalent chromium contaminated soil, and relates to the field of contaminated soil treatment and remediation. The remediation agent for the hexavalent chromium contaminated soil comprises the following raw materials in percentage by mass: 25-40% of a photoinitiator, 5-10% of organic acid and 50-65% of water, the photoinitiator comprises polyethylene glycol. The remediation agent for the hexavalent chromium contaminated soil can reduce hexavalent chromium in the soil into trivalent chromium in situ, and the organic acid can reduce the pH value of the soil, relieve soil salt damage, improve the soil environment and promote crop growth; in addition, the polyethylene glycol and the organic acid can also play a role of a stabilizer to prevent trivalent chromium in the soil from being oxidized into hexavalent chromium, and when the remediation agent is used for treating the chromium-contaminated soil, the remediation agent is simple in equipment requirement, easy and convenient to use, low in cost, high in remediation efficiency, low in operation cost, free of secondary pollution and wide in application and popularization prospect.

Description

Technical Field

[0001] The present application relates to the field of contaminated soil treatment and restoration, and in particular to a repair agent and a repair method for hexavalent chromium contaminated soil. Background Art

[0002] Chromium has a variety of valence states, among which trivalent chromium (Cr(III)) and hexavalent chromium (Cr(VI)) are the most common stable valence states; Cr(III) is widely present in nature and plays an important role in the ecosystem. It has the characteristics of poor water solubility, weak migration ability and low toxicity; Cr(VI) often appears in human industrial production, such as leather making, electroplating, printing and dyeing, textile and ferrochrome smelting. Cr(VI) has the characteristics of being easily soluble in water, having strong migration ability, strong oxidizability and high toxicity (nearly a thousand times the toxicity of Cr(III)). In the process of industrial production and mineral resource mining, a large amount of wastewater or chromium slag with high Cr(VI) content will be generated. With the discharge of chromium wastewater and the erosion of chromium slag by rain and snow, Cr(VI) gradually seeps into the soil or groundwater, thus causing soil pollution problems.

[0003] The remediation methods for chromium-contaminated soil can be mainly divided into two categories. One is to completely remove chromium from the contaminated soil, mainly including chemical leaching or bioremediation technologies. However, chemical leaching will destroy the soil structure, reduce the fertility and suitability of cultivated land, and the leached wastewater needs to be strictly treated. The biological remediation technology requires the selection of suitable plants, and there are problems such as long remediation cycle and poor remediation effect. The other remediation method is to reduce Cr(VI) in the soil to Cr(III), and reduce its negative impact on the environment by changing the existence form of chromium in the soil. The remediation technologies are mainly chemical reduction and biological reduction. The former uses chemical reducing agents such as sodium sulfite, iron filings, ferrous sulfate, and sulfur dioxide to reduce Cr(VI). It is an in-situ remediation method with strong operability and low treatment cost, but the oxidation products produced during the reduction process may cause secondary pollution and are difficult to treat. The latter uses biological reduction reaction to reduce Cr(VI) or convert it into a relatively non-toxic form. It is low cost and has no secondary pollution, but this method is less efficient.

[0004] Developing a chromium-contaminated soil remediation agent that is low-cost, has high remediation efficiency, is easy to use, and can avoid secondary pollution is of great significance to soil management, agricultural production, ecological protection, and promoting the harmonious development of industry and the environment. Summary of the invention

[0005] The purpose of the present application is to provide a remediation agent and remediation method for hexavalent chromium contaminated soil to solve the above problems.

[0006] To achieve the above objectives, the first aspect of the present application provides a remediation agent for hexavalent chromium contaminated soil, wherein the raw materials thereof, calculated by mass as 100%, include:

[0007] Photoinitiator 25%-40%, organic acid 5%-10% and water 50%-65%;

[0008] The photoinitiator includes polyethylene glycol.

[0009] Optionally, the weight average molecular weight of the polyethylene glycol is 200-20000.

[0010] Optionally, the organic acid comprises citric acid.

[0011] The second aspect of the present application provides a method for remediating hexavalent chromium contaminated soil, comprising:

[0012] Under light conditions, the hexavalent chromium contaminated soil and the remediation agent are mixed and reacted.

[0013] Optionally, the hexavalent chromium ion concentration in the hexavalent chromium contaminated soil is 100 mg / kg-10000 mg / kg.

[0014] Optionally, the light source used in the lighting condition is sunlight or artificial light.

[0015] Optionally, the reaction time is 1h-3h.

[0016] Optionally, the pH of the reaction is 4-8.

[0017] Optionally, the mass ratio of the hexavalent chromium contaminated soil to the remediation agent is 1:(0.2-1.8).

[0018] Optionally, the hexavalent chromium-contaminated soil is prepared during mineral processing and smelting, electroplating and leather production.

[0019] Compared with the prior art, the beneficial effects of this application include:

[0020] The remediation agent for hexavalent chromium contaminated soil provided in the present application is a solution, which can better contact with hexavalent chromium in the soil, organic acid combines with hexavalent chromium to convert it into hydrogen chromate, polyethylene glycol is excited under light conditions to undergo charge separation, and the generated conduction band electrons are used to reduce the highly toxic hexavalent hydrogen chromate in the soil to low-toxic trivalent chromium; polyethylene glycol has the characteristics of being flame-retardant, non-explosive, and non-toxic, and can regulate soil properties, increase soil water retention and air permeability, and promote plant growth and development; organic acid can lower soil pH, alleviate soil salt damage, improve soil environment, and promote crop growth; in addition, polyethylene glycol and organic acid can also play the role of stabilizers, can complex with trivalent chromium to prevent the diffusion of chromium elements, and have reducing properties themselves, can provide reducing ability for the soil, prevent trivalent chromium in the soil from being oxidized to hexavalent chromium, and avoid the occurrence of secondary pollution.

[0021] The remediation agent and remediation method for hexavalent chromium contaminated soil provided in the present application can perform soil remediation at room temperature, has a wide range of applications, and can achieve in-situ reduction of hexavalent chromium in the soil to trivalent chromium using sunlight or artificial light. The equipment requirements are simple, the operation is easy, the cost is low, the remediation efficiency is high, the operating cost is low, and no secondary pollution is generated, and the application prospect is broad. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope of the present application.

[0023] Figure 1 A physical picture of the remediation agent for hexavalent chromium contaminated soil provided in Example 1;

[0024] Figure 2 This is a diagram of the restoration process of the method for restoring hexavalent chromium contaminated soil provided in Example 1. DETAILED DESCRIPTION

[0025] As used herein:

[0026] "Prepared from" is synonymous with "comprising." As used herein, the terms "comprising," "including," "having," "containing," or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a composition, process, method, article, or apparatus that comprises the listed elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, process, method, article, or apparatus.

[0027] The conjunction "consisting of excludes any unspecified element, step, or component. If used in a claim, this phrase renders the claim closed-ended so that it does not include materials other than those described, except for conventional impurities associated therewith. When the phrase "consisting of" appears in a clause of the body of a claim rather than immediately following the subject matter, it limits only the elements described in that clause; other elements are not excluded from the claim as a whole.

[0028] When an amount, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper preferred values ​​and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pairing of any range upper limit or preferred value with any range lower limit or preferred value, regardless of whether the range is disclosed separately. For example, when a range of "1 to 5" is disclosed, the described range should be interpreted as including ranges "1 to 4", "1 to 3", "1 to 2", "1 to 2 and 4 to 5", "1 to 3 and 5", etc. When a numerical range is described in this article, unless otherwise stated, the range is intended to include its end values ​​and all integers and fractions within the range.

[0029] In these examples, parts and percentages are by mass unless otherwise indicated.

[0030] "Parts by mass" refers to the basic unit of measurement for expressing the mass ratio of multiple components. 1 part can represent any unit mass, such as 1g or 2.689g. If we say that the mass of component A is a parts and the mass of component B is b parts, it means the ratio of the mass of component A to the mass of component B is a:b. Alternatively, it means that the mass of component A is aK and the mass of component B is bK (K is an arbitrary number, indicating a multiple factor). It should not be misunderstood that, unlike the mass parts, the sum of the mass of all components is not limited to 100 parts.

[0031] "And / or" is used to indicate that one or both of the stated situations may occur, for example, A and / or B includes (A and B) and (A or B).

[0032] It should be noted that hexavalent chromium in the soil mostly exists in the form of solid salt, which is not easy to come into contact with the effective ingredients in the remediation agent, and the remediation efficiency is low; the existing chromium-contaminated soil remediation agents and remediation methods are complicated to operate and have high operating costs; the trivalent chromium in the soil after remediation is very easy to be re-oxidized to hexavalent chromium, causing secondary pollution, and the hexavalent chromium in the soil has high fluidity and toxicity, posing a great threat to the environment and human body.

[0033] The first aspect of the present application provides a remediation agent for hexavalent chromium contaminated soil, wherein the raw materials thereof, calculated by mass as 100%, include:

[0034] Photoinitiator 25%-40%, organic acid 5%-10% and water 50%-65%;

[0035] Optionally, the raw materials of the remediation agent for hexavalent chromium contaminated soil are 100% by mass, the photoinitiator can be 25%, 30%, 35%, 40% or any value between 25% and 40%, the organic acid can be 5%, 6%, 7%, 8%, 9%, 10% or any value between 5% and 10%, and the water can be 50%, 55%, 60%, 65% or any value between 50% and 65%;

[0036] The photoinitiator includes polyethylene glycol.

[0037] In some embodiments, the weight average molecular weight of the polyethylene glycol is 200-20,000.

[0038] Optionally, the weight average molecular weight of the polyethylene glycol can be 200, 1000, 2000, 5000, 10000, 15000, 20000 or any value between 200-20000.

[0039] It should be noted that when the weight-average molecular weight of polyethylene glycol is 200-20000, polyethylene glycol has properties similar to crown ethers, and can form strongly bound complexes with metal ions, which is beneficial to the occurrence of hexavalent chromium photoreduction reaction. If the weight-average molecular weight is too low, it is difficult to reflect this property. If the weight-average molecular weight is too high, not only will the solubility of polyethylene glycol decrease, but the price will also be higher. Therefore, polyethylene glycol with a weight-average molecular weight of 200-20000 has a stronger binding ability with hexavalent chromium, a lower cost, and a better remediation efficiency in the remediation of hexavalent chromium-contaminated soil.

[0040] In some embodiments, the organic acid comprises citric acid.

[0041] It should be noted that citric acid is widely distributed in nature and has the characteristics of being non-toxic and easily soluble in water. It has extremely wide applications in the food industry, metal cleaning, fine chemicals, sterilization and coagulation, and chemical production. When the organic acid is citric acid, it can neutralize alkaline hexavalent chromium-contaminated soil and effectively convert hexavalent chromium into hydrogen chromate; citric acid has a strong chelating effect on trivalent chromium and can fix trivalent chromium, and it has a certain reducing property itself, which can provide a reducing environment for the soil and prevent trivalent chromium from being re-oxidized to hexavalent chromium; citric acid can also promote microbial activity in the soil, increase soil aeration and water retention, improve soil structure, and increase soil fertility.

[0042] The second aspect of the present application provides a method for remediating hexavalent chromium contaminated soil, comprising:

[0043] Under light conditions, the hexavalent chromium contaminated soil and the remediation agent are mixed and reacted.

[0044] In some embodiments, the hexavalent chromium ion concentration in the hexavalent chromium contaminated soil is 100 mg / kg-10000 mg / kg.

[0045] In some embodiments, the light source used in the lighting conditions is sunlight or artificial light.

[0046] In some embodiments, the reaction time is 1 h-3 h.

[0047] Optionally, the reaction time can be 1 h, 2 h, 3 h or any value between 1 h and 3 h.

[0048] In some embodiments, the pH of the reaction is 4-8.

[0049] Optionally, the pH of the reaction can be 4, 5, 6, 7, 8 or any value between 4-8.

[0050] It should be noted that the pH of the reaction is 4-8, which is the pH range after organic acids neutralize alkaline hexavalent chromium-contaminated soil. Within this range, hexavalent chromium is converted into hydrogen chromate, which can promote the reaction. Compared with alkaline soil, there are more hydrogen ions in weakly acidic soil, which can promote microbial activity, accelerate the decomposition of soil organic matter, and release more nutrients. Most plants are also more suitable for growing on neutral or weakly acidic soils.

[0051] Optionally, the pH of the reaction can be 4, 5, 6, 7, 8 or any value between 4-8.

[0052] In some embodiments, the mass ratio of the hexavalent chromium contaminated soil to the remediation agent is 1:(0.2-1.8).

[0053] In some embodiments, the hexavalent chromium contaminated soil is prepared during mineral processing and smelting, electroplating and leather production.

[0054] It should be noted that hexavalent chromium-contaminated soil produced during mineral processing and smelting, electroplating and leather production is highly oxidizing, highly toxic and has a complex morphological distribution, but is usually colorless and odorless, and is difficult to be detected by human sensory organs. It is generally not reflected until it enters the food chain through plants and accumulates to a certain level; hexavalent chromium has a strong migration ability in the soil and can easily spread into the groundwater system through water leaching and other means, thus posing a threat to groundwater safety; hexavalent chromium-contaminated soil can affect crop growth, reduce crop yield and quality; hexavalent chromium in the soil mostly exists in the form of solid salt, which is not easy to come into contact with the active ingredients in the remediation agent, and has low remediation efficiency; existing chromium-contaminated soil remediation agents and remediation methods are complex to operate and have high operating costs; after remediation, trivalent chromium in the soil is easily re-oxidized to hexavalent chromium, causing secondary pollution.

[0055] The application scheme can make hexavalent chromium fully contact with the repair agent, and soil repair can be carried out at room temperature, and has a wide range of applications.

[0056] The embodiments of the present application will be described in detail below in conjunction with specific examples, but it will be appreciated by those skilled in the art that the following examples are only used to illustrate the present application and should not be considered as limiting the scope of the present application. If specific conditions are not specified in the examples, they are carried out according to normal conditions or the conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0057] Example 1

[0058] In a first aspect, the present embodiment provides a remediation agent for hexavalent chromium-contaminated soil, the raw materials of which include:

[0059] 20 g of photoinitiator, 6 g of organic acid and 40 g of water, wherein the photoinitiator is polyethylene glycol with a weight average molecular weight of 8000, and the organic acid is citric acid;

[0060] A second aspect of this embodiment provides a method for remediating hexavalent chromium-contaminated soil, comprising:

[0061] In a glass container, 39.43 g of chromium-free soil and 0.57 g of potassium dichromate were added to prepare 40 g of simulated hexavalent chromium-contaminated soil. The Cr(VI) content in the hexavalent chromium-contaminated soil was 5000 mg / kg. 66 g of a repair agent was added and mixed evenly. The pH was 5.5. The soil was placed in sunlight and turned for 2 hours. 95% of the hexavalent chromium could be reduced to trivalent chromium.

[0062] The physical remediation agent for hexavalent chromium contaminated soil in this embodiment is as follows: Figure 1 shown.

[0063] The repair process of this embodiment is as follows Figure 2 shown.

[0064] Example 2

[0065] In a first aspect, the present embodiment provides a remediation agent for hexavalent chromium-contaminated soil, the raw materials of which include:

[0066] 20 g of photoinitiator, 6 g of organic acid and 40 g of water, wherein the photoinitiator is polyethylene glycol with a weight average molecular weight of 6000, and the organic acid is citric acid;

[0067] A second aspect of this embodiment provides a method for remediating hexavalent chromium-contaminated soil, comprising:

[0068] In a glass container, 40 g of hexavalent chromium-contaminated soil produced by a chromium chemical company during production was added. The Cr(VI) content in the hexavalent chromium-contaminated soil was 5753 mg / kg. 66 g of a repair agent was added and mixed evenly. The pH value was 5. The soil was placed in sunlight and stirred for 2 hours. 94% of the hexavalent chromium could be reduced to trivalent chromium.

[0069] Example 3

[0070] In a first aspect, the present embodiment provides a remediation agent for hexavalent chromium-contaminated soil, the raw materials of which include:

[0071] 50 g of photoinitiator, 15 g of organic acid and 100 g of water, wherein the photoinitiator is polyethylene glycol with a weight average molecular weight of 2000, and the organic acid is citric acid;

[0072] A second aspect of this embodiment provides a method for remediating hexavalent chromium-contaminated soil, comprising:

[0073] In a glass container, hexavalent chromium-contaminated soil produced in the process of mineral processing and smelting is added. In a glass container, 199.43g of chromium-free soil and 0.57g of potassium dichromate are added to prepare 200g of simulated hexavalent chromium-contaminated soil. The Cr(VI) content in the hexavalent chromium-contaminated soil is 1000mg / kg. 165g of a repair agent is added and mixed evenly. The pH is 4.5. The mixture is placed in sunlight and turned for 2h. 96% of the hexavalent chromium can be reduced to trivalent chromium.

[0074] Example 4

[0075] In a first aspect, the present embodiment provides a remediation agent for hexavalent chromium-contaminated soil, the raw materials of which include:

[0076] 75 g of photoinitiator, 18 g of organic acid and 100 g of water, wherein the photoinitiator is polyethylene glycol with a weight average molecular weight of 400, and the organic acid is citric acid;

[0077] A second aspect of this embodiment provides a method for remediating hexavalent chromium-contaminated soil, comprising:

[0078] 500 g of hexavalent chromium-contaminated soil produced during the electroplating process was added into a glass container. The Cr(VI) content in the hexavalent chromium-contaminated soil was 500 mg / kg. 193 g of a repair agent was added and mixed evenly. The pH value was 4. The container was placed under sunlight and stirred for 2 hours. 98% of the hexavalent chromium could be reduced to trivalent chromium.

[0079] Comparative Example 1

[0080] This comparative example provides a repair agent for hexavalent chromium-contaminated soil, which is different from Example 1 in that no photoinitiator is added in this comparative example.

[0081] In this comparative example, the same batch of hexavalent chromium contaminated soil was remediated using the same remediation method as in Example 1, and 5% of the hexavalent chromium was reduced to trivalent chromium.

[0082] Comparative Example 2

[0083] This comparative example provides a repair agent for hexavalent chromium contaminated soil, which is different from Example 1 in that the photoinitiator of this comparative example is 2-benzyl-2-dimethylamino-1-(4-morpholinephenyl)butanone.

[0084] In this comparative example, the same batch of hexavalent chromium contaminated soil was remediated using the same remediation method as in Example 1, and 5% of the hexavalent chromium was reduced to trivalent chromium.

[0085] Comparative Example 3

[0086] This comparative example provides a repair agent for hexavalent chromium contaminated soil, which is different from Example 1 in that no organic acid is added in this comparative example.

[0087] In this comparative example, the same batch of hexavalent chromium contaminated soil was remediated using the same remediation method as in Example 1, and 20% of the hexavalent chromium was reduced to trivalent chromium.

[0088] Comparative Example 4

[0089] This comparative example provides a repair agent for hexavalent chromium-contaminated soil, and its raw materials include:

[0090] 15% photoinitiator, 3% organic acid and 82% water, wherein the photoinitiator is polyethylene glycol with a weight average molecular weight of 2000, and the organic acid is citric acid;

[0091] In this comparative example, the same batch of hexavalent chromium contaminated soil was remediated using the same remediation method as in Example 1, and 61% of the hexavalent chromium could be reduced to trivalent chromium.

[0092] It can be seen from the above embodiments and comparative examples that the use of polyethylene glycol or citric acid alone can hardly reduce the hexavalent chromium in the soil, and the use of other commonly used photoinitiators also cannot reduce the hexavalent chromium in the soil. Polyethylene glycol and citric acid play a synergistic role in the reduction of hexavalent chromium in the soil; in addition, if the applied raw material ratio is not used, the reduction effect of the repair agent will be greatly reduced, and it is difficult to meet the requirements for the remediation of chromium-contaminated soil.

[0093] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit it. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application.

[0094] In addition, those skilled in the art will appreciate that, although some embodiments herein include certain features included in other embodiments but not other features, the combination of features of different embodiments is meant to be within the scope of the present application and form different embodiments. For example, in the above claims, any one of the claimed embodiments may be used in any combination. The information disclosed in this background technology section is intended only to deepen the understanding of the overall background technology of the present application and should not be regarded as an admission or in any form of implication that the information constitutes prior art known to those skilled in the art.

Claims

1. A remediation agent for hexavalent chromium contaminated soil, characterized in that: The raw materials thereof, calculated by mass as 100%, include: Photoinitiator 25%-40%, organic acid 5%-10% and water 50%-65%; The photoinitiator includes polyethylene glycol.

2. The remediation agent for hexavalent chromium contaminated soil according to claim 1, characterized in that: The weight average molecular weight of the polyethylene glycol is 200-20000.

3. The remediation agent for hexavalent chromium contaminated soil according to claim 1, characterized in that: The organic acid includes citric acid.

4. A method for remediating hexavalent chromium contaminated soil, characterized in that: include: Under light conditions, the hexavalent chromium contaminated soil and the repair agent according to any one of claims 1 to 3 are mixed and reacted.

5. The method for remediating hexavalent chromium contaminated soil according to claim 4, characterized in that: The hexavalent chromium ion concentration in the hexavalent chromium contaminated soil is 100 mg / kg-10000 mg / kg.

6. The method for remediating hexavalent chromium contaminated soil according to claim 4, characterized in that: The light source used in the illumination conditions is sunlight or artificial light source.

7. The method for remediating hexavalent chromium contaminated soil according to claim 4, characterized in that: The reaction time is 1 h-3 h.

8. The method for remediating hexavalent chromium contaminated soil according to claim 4, characterized in that: The pH of the reaction is 4-8.

9. The method for remediating hexavalent chromium contaminated soil according to claim 4, characterized in that: The mass ratio of the hexavalent chromium contaminated soil to the repair agent is 1:(0.2-1.8).

10. The method for remediating hexavalent chromium contaminated soil according to any one of claims 4 to 9, characterized in that: The hexavalent chromium contaminated soil is prepared during the process of mineral processing, smelting, electroplating and leather production.

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