A Remediation Agent and Remediation Method for Chromium(VI)-Contaminated Soil

Abstract

The present application provides a remediating agent and a remediation method for hexavalent chromium contaminated soil, which relates to the field of treatment and remediation of contaminated soil. Based on 100% by mass, the raw materials of the remediating agent for hexavalent chromium contaminated soil include: 25%-40% of photoinitiator, 5%-10% of organic acid, and 50%-65% of water; the photoinitiator includes polyethylene glycol. The remediating agent for hexavalent chromium contaminated soil can in-situ reduce hexavalent chromium in the soil to trivalent chromium. The organic acid can reduce the soil pH value, alleviate soil salt damage, improve the soil environment, and promote crop growth; polyethylene glycol and the organic acid can also act as stabilizers to prevent trivalent chromium in the soil from being oxidized to hexavalent chromium. Using this remediating agent to treat chromium contaminated soil has simple equipment requirements, is easy to use, has low costs, high remediation efficiency, low operating costs, does not produce secondary pollution, and has broad prospects for popularization and application.

Description

Technical Field

[0001] This application relates to the field of contaminated soil treatment and remediation, and particularly to a remediation agent and a remediation method for hexavalent chromium contaminated soil. Background Art

[0002] Among numerous chemical pollutants, chromium is one of the most common and severely harmful pollutants. Chromium has multiple valence states, among which trivalent chromium (Cr(III)) and hexavalent chromium (Cr(VI)) are the most common stable valence states; Cr(III) widely exists in nature and plays an important role in the ecosystem. It has characteristics such as poor water solubility, weak migration ability, and low toxicity; Cr(VI) mostly appears in human industrial production, such as leather making, electroplating, printing and dyeing, textile, and ferrochrome smelting. Cr(VI) has characteristics such as being easily soluble in water, strong migration ability, strong oxidizing property, and high toxicity (nearly a thousand times the toxicity of Cr(III)). During industrial production and mineral resource exploitation, a large amount of wastewater or chromium slag with a high Cr(VI) content will be generated. With the discharge of chromium wastewater and the leaching of chromium slag by rain and snow, Cr(VI) gradually seeps into the soil or groundwater, thus triggering 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 technologies such as chemical leaching or bioremediation. However, chemical leaching will damage the soil structure, reduce the fertility and tillability of arable land, and the leached wastewater needs to be strictly treated. And the bioremediation technology requires selecting suitable plants, and there are problems such as a 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 existing form of chromium in the soil. The remediation technologies are mainly chemical reduction method and biological reduction method. The former uses chemical reducing agents such as sodium sulfite, iron filings, ferrous sulfate, sulfur dioxide, etc. to reduce Cr(VI), which belongs to an in-situ remediation method, with strong operability and low treatment cost. However, the oxidation products generated during the reduction process may cause secondary pollution and are difficult to treat. The latter uses biological reduction reactions to reduce Cr(VI) or convert it into a relatively non-toxic form, with low cost and no secondary pollution, but this method has low efficiency.

[0004] Considering that the existing chromium contaminated soil remediation agents and remediation methods have a series of problems such as high operating costs, complex operations, low efficiency, easy to cause secondary pollution, and difficult to promote and apply, developing a chromium contaminated soil remediation agent with low cost, high remediation efficiency, easy to use, and capable of avoiding secondary pollution has important strategic significance for soil treatment, agricultural production, ecological protection, and promoting the harmonious development of industry and the environment. Summary of the Invention

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

[0006] To achieve the above object, the first aspect of the present application provides a remediating agent for hexavalent chromium contaminated soil. Calculated by mass as 100%, its raw materials include:

[0007] 25%-40% of a photoinitiator, 5%-10% of an organic acid, and 50%-65% of water;

[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 includes citric acid.

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

[0012] Mixing and reacting the hexavalent chromium contaminated soil and the above-mentioned remediating agent under light conditions.

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

[0014] Optionally, the light source used for the light conditions is sunlight or an artificial light source.

[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 remediating agent is 1:(0.2 - 1.8).

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

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

[0020] The chromium(VI)-contaminated soil remediation agent provided by this application is a solution, which can better contact with chromium(VI) in the soil. The organic acid combines with chromium(VI) to convert it into hydrogen chromate. Under the condition of light irradiation, polyethylene glycol is excited to generate charge separation, and the conduction band electrons generated are used to reduce the highly toxic hydrogen chromate in the soil to low-toxicity trivalent chromium; Polyethylene glycol has the characteristics of being flame-retardant, non-explosive, non-toxic, etc., can adjust the soil properties, increase the water retention and aeration of the soil, and promote plant growth and development; Organic acids can reduce the soil pH value, relieve soil salt damage, improve the soil environment, and promote crop growth; In addition, polyethylene glycol and organic acids can also play the role of stabilizers, can complex with trivalent chromium to prevent the diffusion of chromium elements, and have reducibility themselves, can provide reduction ability for the soil, prevent the trivalent chromium in the soil from being oxidized to hexavalent chromium, and avoid the occurrence of secondary pollution.

[0021] The chromium(VI)-contaminated soil remediation agent and remediation method provided by this application can carry out soil remediation at room temperature, have a wide application range, can use sunlight or artificial light to realize the in-situ reduction of chromium(VI) in the soil to trivalent chromium, have simple equipment requirements, are easy to operate, have low costs, high remediation efficiency, low operating costs, will not produce secondary pollution, and have broad application prospects for popularization. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0023] Figure 1 It is a physical diagram of the chromium(VI)-contaminated soil remediation agent provided for Example 1;

[0024] Figure 2 It is a remediation process diagram of the chromium(VI)-contaminated soil remediation method provided for Example 1. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] As used herein, the terms:

[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 non-exclusive inclusion. For example, a composition, step, method, article or device containing the listed elements does not have to be limited to those elements, but may include other elements not expressly listed or elements inherent to such composition, step, method, article or device.

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

[0028] When an equivalent, 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 to specifically disclose all ranges formed by any pairing of any range upper limit or preferred value with any range lower limit or preferred value, whether or not that range is separately disclosed. For example, when the range "1 - 5" is disclosed, the described range should be interpreted to include ranges "1 - 4", "1 - 3", "1 - 2", "1 - 2 and 4 - 5", "1 - 3 and 5", etc. When a numerical range is described herein, unless otherwise stated, the range is intended to include its endpoint values and all integers and fractions within that range.

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

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

[0031] "And / or" is used to indicate that either or both of the stated circumstances 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 soil mostly exists in the form of solid salts, making it difficult to come into contact with the active ingredients in the remediation agent, resulting in low remediation efficiency; existing chromium - contaminated soil remediation agents and remediation methods are complex in operation and high in operating cost; trivalent chromium in the soil after remediation is extremely easy to be re - oxidized to hexavalent chromium, causing secondary pollution, and hexavalent chromium in the soil has high mobility 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. Calculated based on 100% by mass of the raw materials, it includes:

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

[0035] Optionally, based on 100% by mass of the raw materials of the remediator for hexavalent chromium contaminated soil, 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 polyethylene glycol has a weight-average molecular weight of 200-20000.

[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 and 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 complexes with strong binding with metal ions, which is beneficial to the occurrence of the photoreduction reaction of hexavalent chromium. If the weight-average molecular weight is too low, this property is difficult to be reflected. If the weight-average molecular weight is too high, not only the solubility of polyethylene glycol will 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, lower cost, and better remediation efficiency in the remediation of hexavalent chromium contaminated soil.

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

[0041] It should be noted that citric acid is widely distributed in nature and has characteristics such as non-toxicity and easy solubility in water. It has extremely wide applications in the fields of food industry, metal cleaning, fine chemicals, bactericidal coagulation, and chemical production. When the organic acid is citric acid, it can neutralize the alkaline hexavalent chromium contaminated soil and effectively convert hexavalent chromium into chromium hydrogen salt; citric acid has a strong complexing effect on trivalent chromium, can fix trivalent chromium, and has certain reducibility itself, which can provide a reducing environment for the soil to prevent trivalent chromium from being re-oxidized to hexavalent chromium; citric acid can also promote the activities of microorganisms in the soil, increase the aeration and water retention of the soil, improve the soil structure, and increase the soil fertility.

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

[0043] Under light conditions, mix and react the hexavalent chromium contaminated soil with the described remediation agent.

[0044] In some embodiments, the concentration of hexavalent chromium ions in the hexavalent chromium contaminated soil is 100 mg / kg - 10,000 mg / kg.

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

[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 - 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 the organic acid neutralizes the alkaline hexavalent chromium contaminated soil. Within this range, hexavalent chromium is converted into hydrogen chromate, which can promote the reaction to occur; compared with alkaline soil, there are more hydrogen ions in weakly acidic soil, which can promote microbial activities, accelerate the decomposition of soil organic matter, release more nutrients, and most plants are also more suitable to grow in neutral or weakly acidic soil.

[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 the processes of mineral processing and smelting, electroplating, and leather production.

[0054] It should be noted that treating hexavalent chromium - contaminated soil generated during mineral processing, smelting, electroplating, and tanning production processes has high oxidizing property, high toxicity, and complex morphological distribution. It is usually colorless and odorless, making it difficult to be detected by human sensory organs. Generally, it can only be reflected when it accumulates to a certain extent through plants entering the food chain. Hexavalent chromium has strong migration ability in soil and is easily diffused into the groundwater system through ways such as water leaching, thus threatening the safety of groundwater. Hexavalent chromium - contaminated soil will affect crop growth and reduce crop yield and quality. Most of the hexavalent chromium in soil exists in the form of solid salts, making it difficult to come into contact with the active ingredients in the remediation agent, resulting in low remediation efficiency. Existing chromium - contaminated soil remediation agents and remediation methods are complex in operation and high in operating cost. Trivalent chromium in the soil after remediation is extremely easy to be re - oxidized to hexavalent chromium, causing secondary pollution.

[0055] The solution of this application can enable hexavalent chromium to fully contact with the remediation agent, and soil remediation can be carried out at room temperature, with a wide range of applications.

[0056] The following will describe the implementation plan of this application in detail with specific examples. However, those skilled in the art will understand that the following examples are only used to illustrate this application and should not be regarded as limiting the scope of this application. For those not specified in the examples, they are carried out according to conventional conditions or the conditions recommended by the manufacturer. For reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0057] Example 1

[0058] In the first aspect of this example, a remediation agent for hexavalent chromium - contaminated soil is provided, and its raw materials include:

[0059] 20 g of photo - initiator, 6 g of organic acid, and 40 g of water. Among them, the photo - initiator is polyethylene glycol with a weight - average molecular weight of 8000, and the organic acid is citric acid;

[0060] In the second aspect of this example, a remediation method for hexavalent chromium - contaminated soil is provided, including:

[0061] Add 39.43 g of chromium - free soil and 0.57 g of potassium dichromate into a glassware to prepare 40 g of simulated hexavalent chromium - contaminated soil. The Cr(VI) content in the hexavalent chromium - contaminated soil is 5000 mg / kg. Add 66 g of the remediation agent and mix evenly. The pH is 5.5. Place it under sunlight and turn it over for 2 h. 95% of the hexavalent chromium can be reduced to trivalent chromium.

[0062] The physical object of the remediation agent for hexavalent chromium - contaminated soil in this example is as Figure 1 shown.

[0063] The remediation process in this example is as Figure 2 shown.

[0064] Example 2

[0065] In the first aspect of this example, a remediation agent for hexavalent chromium contaminated soil is provided, and its raw materials include:

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

[0067] In the second aspect of this example, a method for remediating hexavalent chromium contaminated soil is provided, including:

[0068] Add 40 g of hexavalent chromium contaminated soil generated during the production process of a chromium chemical enterprise to a glassware. The Cr(VI) content in the hexavalent chromium contaminated soil is 5753 mg / kg. Add 66 g of the remediation agent and mix evenly. The pH is 5. Place it under sunlight and turn it over for 2 h. 94% of the hexavalent chromium can be reduced to trivalent chromium.

[0069] Example 3

[0070] In the first aspect of this example, a remediation agent for hexavalent chromium contaminated soil is provided, and its raw materials include:

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

[0072] In the second aspect of this example, a method for remediating hexavalent chromium contaminated soil is provided, including:

[0073] Add 199.43 g of chromium-free soil and 0.57 g of potassium dichromate to a glassware to prepare 200 g of simulated hexavalent chromium contaminated soil. The Cr(VI) content in the hexavalent chromium contaminated soil is 1000 mg / kg. Add 165 g of the remediation agent and mix evenly. The pH is 4.5. Place it under sunlight and turn it over for 2 h. 96% of the hexavalent chromium can be reduced to trivalent chromium.

[0074] Example 4

[0075] In the first aspect of this example, a remediation agent for hexavalent chromium contaminated soil is provided, and its raw materials include:

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

[0077] In the second aspect of this example, a method for remediating hexavalent chromium contaminated soil is provided, including:

[0078] Add 500 g of hexavalent chromium - contaminated soil generated during the electroplating process to a glassware. The Cr(VI) content in the hexavalent chromium - contaminated soil is 500 mg / kg. Add 193 g of the remediation agent and mix evenly. The pH is 4. Place it under sunlight and turn it over for 2 h. 98% of the hexavalent chromium can be reduced to trivalent chromium.

[0079] Comparative Example 1

[0080] This comparative example provides a remediation agent for hexavalent chromium - contaminated soil. The difference from Example 1 is that this comparative example does not add a photo - initiator.

[0081] This comparative example repairs the same batch of hexavalent chromium - contaminated soil according to the same remediation method as in Example 1. 5% of the hexavalent chromium can be reduced to trivalent chromium.

[0082] Comparative Example 2

[0083] This comparative example provides a remediation agent for hexavalent chromium - contaminated soil. The difference from Example 1 is that the photo - initiator in this comparative example is 2 - benzyl - 2 - dimethylamino - 1 - (4 - morpholinophenyl) butanone.

[0084] This comparative example repairs the same batch of hexavalent chromium - contaminated soil according to the same remediation method as in Example 1. 5% of the hexavalent chromium can be reduced to trivalent chromium.

[0085] Comparative Example 3

[0086] This comparative example provides a remediation agent for hexavalent chromium - contaminated soil. The difference from Example 1 is that this comparative example does not add organic acid.

[0087] This comparative example repairs the same batch of hexavalent chromium - contaminated soil according to the same remediation method as in Example 1. 20% of the hexavalent chromium can be reduced to trivalent chromium.

[0088] Comparative Example 4

[0089] This comparative example provides a remediation agent for hexavalent chromium - contaminated soil. Its raw materials include:

[0090] 15% photo - initiator, 3% organic acid, and 82% water. Among them, the photo - initiator is polyethylene glycol with a weight - average molecular weight of 2000, and the organic acid is citric acid;

[0091] This comparative example repairs the same batch of hexavalent chromium - contaminated soil according to the same remediation method as in Example 1. 61% of the hexavalent chromium can be reduced to trivalent chromium.

[0092] As can be seen from the above embodiments and comparative examples, neither polyethylene glycol nor citric acid alone can hardly reduce hexavalent chromium in soil. Selecting other commonly used photoinitiators also fails to reduce hexavalent chromium in soil. Polyethylene glycol and citric acid play a synergistic role in the reduction process of hexavalent chromium in soil. In addition, without using the raw material ratio of the application, the reduction effect of the repair agent will be greatly reduced and it is difficult to meet the requirements for the repair 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 them. Although the present application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features. 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 can understand that although some embodiments herein include certain features included in other embodiments rather than other features, the combination of the features of different embodiments means that it is within the scope of the present application and forms different embodiments. For example, in the above claims, any one of the claimed embodiments can be used in any combination. The information disclosed in this background art section is only intended to deepen the understanding of the overall background art of the present application, and should not be regarded as an admission or any form of implication that this information constitutes prior art known to those skilled in the art.

Claims

1. A method for remediating hexavalent chromium contaminated soil, characterized in that: include: Under light conditions, the hexavalent chromium contaminated soil and the remediation agent are mixed and reacted; The raw materials of the repair agent are calculated by mass as 100%, which are: Photoinitiator 25%-40%, organic acid 5%-10% and water 50%-65%; The photoinitiator is polyethylene glycol; The weight average molecular weight of the polyethylene glycol is 200-20000; The organic acid is citric acid; The pH of the reaction is 6-8; The mass ratio of the hexavalent chromium contaminated soil to the repair agent is 1:(0.2-1.8); the hexavalent chromium contaminated soil is prepared during the process of mineral processing, smelting, electroplating and leather production.

2. The method for remediating hexavalent chromium contaminated soil according to claim 1, characterized in that: The hexavalent chromium ion concentration in the hexavalent chromium contaminated soil is 100 mg / kg-10000 mg / kg.

3. The method for remediating hexavalent chromium contaminated soil according to claim 1, characterized in that: The light source used in the illumination conditions is sunlight or artificial light source.

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

Images