A remediation agent for high-concentration hexavalent chromium contaminated soil, a preparation method and a remediation method thereof

Abstract

The application discloses a remediation agent for high-concentration hexavalent chromium contaminated soil and a preparation method and a remediation method thereof, and belongs to the technical field of soil pollution remediation. The remediation agent for high-concentration hexavalent chromium contaminated soil comprises an acid precursor, an iron-sulfur reducing agent and a synergist; the acid precursor comprises an organic acid and alginate propylene glycol ester; the iron-sulfur reducing agent comprises an iron-based reducing agent and a sulfur-based reducing agent; and the synergist comprises sophorolipid and alkyl glucoside. The remediation agent can be used for high-concentration hexavalent chromium contaminated soil, can replace hexavalent chromium in the soil as much as possible to expose Cr 6+ in the form of ions, and then convert the Cr into trivalent chromium by using a reducing agent, so that the removal efficiency of hexavalent chromium is as high as 99.6%. In addition, the soil remediation agent is simple to use, and has rapid and thorough reaction and long-lasting effect.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of soil pollution remediation, and particularly relates to a remediation agent for high-concentration hexavalent chromium contaminated soil and a preparation method and a remediation method thereof. BACKGROUND

[0002] Chromium is an important strategic metal resource, and its application fields are very wide, including metallurgy, pigments, tanning, wood preservation, electroplating, medicine, organic synthesis, dyes, chemical agents, ceramics, glass, petroleum exploitation, printing plate making, catalysts, magnetic materials, metal corrosion inhibition, metal polishing and other process flows. It is related to 15% of commodity varieties in China and is irreplaceable.

[0003] Chromium chemical industry, tanning and electroplating are the most important chromium-related industries, and at the same time, there is a serious problem of chromium-contaminated soil.

[0004] At present, the remediation technology for chromium-contaminated soil is mainly based on the reduction and stabilization principle of hexavalent chromium, and specifically includes chemical reduction, chemical leaching, electrodynamic remediation and biological remediation technology, etc. Considering the technical applicability and economy, the chemical reduction remediation technology is still mostly used in chromium-contaminated soil remediation engineering. The chemical reduction method mainly converts the highly toxic Cr(Ⅵ) into low-toxic and difficult-to-migrate Cr(Ⅲ) precipitate through reduction reaction. Common reducing agents include FeSO4, FeO, calcium polysulfide and reducing microorganisms, etc. This method can effectively reduce the migration ability and bioavailability of chromium. For example, Chinese patent CN 110079321A discloses a preparation and use method of a hexavalent chromium contaminated soil remediation agent. The highest concentration of Cr(Ⅵ) in the original soil is 2500mg / kg, and the concentration of Cr(Ⅵ) after remediation is less than 0.1mg / L. However, the total amount of Cr(Ⅵ) after remediation is not concerned. Chinese patent CN110302746A discloses a composite material for hexavalent chromium contaminated water or soil remediation and a preparation method thereof. The addition of 5% of the composite material can reduce the total amount of hexavalent chromium in the soil from about 424mg / kg to about 39mg / kg. However, the total amount of hexavalent chromium after remediation is still 13 times the GB 36600 first-class land screening value. 6+ Although the leaching concentration is lower than 0.1mg / L, the total amount of Cr(Ⅵ) after remediation is not concerned. Chinese patent CN110302746A discloses a composite material for hexavalent chromium contaminated water or soil remediation and a preparation method thereof. The addition of 5% of the composite material can reduce the total amount of hexavalent chromium in the soil from about 424mg / kg to about 39mg / kg. However, the total amount of hexavalent chromium after remediation is still 13 times the GB 36600 first-class land screening value.

[0005] Therefore, it is urgent to develop a remediation agent to deal with high-concentration hexavalent chromium contaminated soil in chromium-contaminated sites and meet the requirements of relevant national standards for the total amount of hexavalent chromium. SUMMARY

[0006] The present application provides a remediation agent for high-concentration hexavalent chromium contaminated soil and a preparation method and a remediation method thereof to solve the problems and defects of existing hexavalent chromium remediation materials.

[0007] To achieve the above technical purposes, the technical scheme adopted by the present application is:

[0008] A remediation agent for high-concentration hexavalent chromium contaminated soil, taking 100g of hexavalent chromium contaminated soil as an example, the remediation agent comprises the following amount of raw materials: 2.8-6g of acid precursor, 4-6g of iron-sulfur reducing agent, and 1-2g of synergistic agent; the acid precursor comprises organic acid and propylene glycol alginate; the iron-sulfur reducing agent comprises iron-based material and sulfur-based material; and the synergistic agent comprises sophorolipid and alkyl glucoside.

[0009] Further, the organic acid is one or more of oxalic acid, citric acid, and tartaric acid; the iron-based material is one or more of ferrous sulfate, ferrous chloride, and zero-valent iron; and the sulfur-based material is one or more of sodium thiosulfate, sodium metabisulfite, and calcium polysulfide.

[0010] Further, the mass ratio of sophorolipid to alkyl glucoside in the synergistic agent is 1:1.

[0011] Further, the mass ratio of the organic acid to propylene glycol alginate is (2.5-5):1.

[0012] Further, the mass ratio of the iron-based material to the sulfur-based material is 4:1.

[0013] A preparation method of a remediation agent for high-concentration hexavalent chromium contaminated soil, comprising the following steps:

[0014] S1: organic acid powder is added to 50ml of ultrapure water, and after ultrasonic dissolution in an oxygen-free or low-oxygen environment, an organic acid liquid is obtained, which is stored at ≤20℃ for standby use; after adding propylene glycol alginate to the above-mentioned organic acid liquid and adding ultrapure water to a constant volume of 100ml, a homogeneous mixture is obtained to obtain an acid precursor colloidal solution, which is divided and stored;

[0015] S2: sophorolipid and alkyl glucoside are added to 20ml of ultrapure water and fully dissolved to obtain a synergistic agent solution, which is divided and stored;

[0016] S3: after the iron-based material is dried to remove free water, the dried iron-based material and the sulfur-based material are mixed uniformly, ground to 50-100 mesh, and an iron-sulfur reducing agent is obtained, which is divided and stored.

[0017] A remediation method of a remediation agent for high-concentration hexavalent chromium contaminated soil, comprising the following steps:

[0018] The air-dried contaminated soil is taken, the acid precursor colloidal solution and the synergistic agent solution are added, and stirring reaction is carried out for 2-4h, the iron-sulfur reducing agent is added, stirring is carried out for 15-30min, and standing and curing are carried out for 3-5 days.

[0019] Further, the contaminated soil is sieved to 10 mesh.

[0020] The raw materials used in the present application are commercially available.

[0021] The soil remediation agent provided by the present application reduces the total amount of hexavalent chromium in the soil by reducing the high-toxicity hexavalent chromium to low-toxicity trivalent chromium.

[0022] The acid precursor provided by the present application comprises an organic acid and propylene glycol alginate. When the organic acid is added to the soil solution containing calcium chromate solid solution, the organic acid combines with calcium ions in the solution to generate calcium salt precipitation. As the content of calcium ions in the solution decreases, the chromium acid ions are precipitated again to maintain the constant Ksp of the calcium chromate precipitate. However, the propylene glycol alginate prevents the re-formation of the calcium chromate precipitate. At this time, the reducing agent is added to reduce the exposed Cr 6+ to Cr 3+ , and the soil is kept in a reducing environment to avoid "yellowing".

[0023] The synergist consists of sophorolipid and alkyl glucoside. Sophorolipid is a biological surfactant, and alkyl glucoside is a non-ionic surfactant. The two are compounded and show significant effects in soil remediation. On the one hand, the surface tension of water is reduced, the penetration ability of the acid precursor to the soil is enhanced, and the Cr 6+ exposed to the soil particles is accelerated. On the other hand, the added synergist can increase the solubility of the chromium acid ions, making it easier to expose the chromium acid ions of the calcium chromate solidified in the soil particles. Therefore, the synergist can increase the solubilization and desorption rate of chromium ions in the soil, thereby improving the removal efficiency of high-concentration hexavalent chromium.

[0024] Advantages

[0025] The present application is mainly applied to high-concentration hexavalent chromium contaminated soil and solves the problem that the hexavalent chromium solidified in the soil particles cannot be reduced by only adding a reducing agent. The composition and method of the present application can remove as much hexavalent chromium as possible from the soil, especially for soil rich in calcium chromate, the effect is more obvious. Compared with the treatment of prolonging the soaking time and increasing the soaking times, the present application has higher hexavalent chromium removal rate and higher treatment efficiency.

[0026] The soil remediation agent provided by the present application has the characteristics of simple adding method, rapid and complete reaction, and long-lasting effect, and is especially suitable for high-concentration hexavalent chromium contaminated soil. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 The flowchart of the present application. DETAILED DESCRIPTION

[0028] The technical solutions of the application are further described below in combination with specific examples, but are not limited thereto.

[0029] Example 1

[0030] A preparation method of a remediation agent for high-concentration hexavalent chromium contaminated soil, comprising the following steps:

[0031] 5g of oxalic acid powder is added to 50ml of ultrapure water, and after ultrasonic dissolution in an oxygen-free or low-oxygen environment, an organic acid liquid is obtained, which is stored at ≤20℃ for standby use; 1g of propylene glycol alginate is added to the above-mentioned organic acid liquid, and ultrapure water is added to make up to 100ml, and then mixed uniformly to obtain an acidic precursor colloid solution;

[0032] 1g of sophorolipid and 1g of alkyl glucoside are added to 20ml of ultrapure water and dissolved to obtain a synergist solution;

[0033] After drying and removing free water, 4g of dried ferrous sulfate and 1g of sodium thiosulfate are mixed uniformly, ground to 50-100 meshes, and an iron-sulfur reducing agent is obtained.

[0034] A remediation method of a remediation agent for high-concentration hexavalent chromium contaminated soil, comprising the following steps:

[0035] 100g of contaminated soil dried and passed through a 10-mesh nylon screen is placed in a 500ml beaker, the prepared acidic precursor colloid solution and synergist solution are added, stirred and reacted for 4h, the prepared iron-sulfur reducing agent is then added, stirred for 30min, and left to stand for 5 days.

[0036] Example 2

[0037] A preparation method of a remediation agent for high-concentration hexavalent chromium contaminated soil, comprising the following steps:

[0038] 3g of citric acid powder is added to 50ml of ultrapure water, and after ultrasonic dissolution in an oxygen-free or low-oxygen environment, an organic acid liquid is obtained, which is stored at ≤20℃ for standby use; 0.6g of propylene glycol alginate is added to the above-mentioned organic acid liquid, and ultrapure water is added to make up to 100ml, and then mixed uniformly to obtain an acidic precursor colloid solution;

[0039] 0.5g of sophorolipid and 0.5g of alkyl glucoside are added to 20ml of ultrapure water and dissolved to obtain a synergist solution;

[0040] After drying and removing free water, 2g of dried ferrous chloride and 1g of sodium metabisulfite are mixed uniformly, ground to 50-100 meshes, and an iron-sulfur reducing agent is obtained.

[0041] A remediation method of a remediation agent for high-concentration hexavalent chromium contaminated soil, comprising the following steps:

[0042] Take 100 g of contaminated soil dried and passed through a 10-mesh nylon screen, place it in a 500-ml beaker, add the prepared acid precursor colloid solution and synergist solution, stir for 3 h, then add the prepared iron-sulfur reducing agent, stir for 20 min, and let it stand for 4 days.

[0043] Example 3

[0044] A preparation method of a remediation agent for high-concentration hexavalent chromium contaminated soil, comprising the following steps:

[0045] Add 2 g of tartaric acid powder to 50 ml of ultrapure water, ultrasonically dissolve in an oxygen-free or low-oxygen environment, and obtain an organic acid liquid, which is stored at ≤20℃ for standby; add 0.8 g of propylene glycol alginate to the above organic acid liquid, and add ultrapure water to 100 ml, and mix uniformly to obtain an acid precursor colloid solution;

[0046] Add 0.5 g of sophorose lipid and 0.5 g of alkyl glucoside to 20 ml of ultrapure water, and dissolve thoroughly to obtain a synergist solution;

[0047] After removing free water, mix 3 g of dried zero-valent iron and 1 g of calcium polysulfide uniformly, grind to 50-100 mesh, and obtain an iron-sulfur reducing agent.

[0048] A remediation method of a remediation agent for high-concentration hexavalent chromium contaminated soil, comprising the following steps:

[0049] Take 100 g of contaminated soil dried and passed through a 10-mesh nylon screen, place it in a 500-ml beaker, add the prepared acid precursor colloid solution and synergist solution, stir for 2 h, then add the prepared iron-sulfur reducing agent, stir for 15 min, and let it stand for 3 days.

[0050] Comparative Example 1

[0051] This comparative example is compared with Example 1, except that no propylene glycol alginate is added to the acid precursor, and the remaining raw materials and steps are the same as those of Example 1.

[0052] Comparative Example 2

[0053] This comparative example is compared with Example 1, except that no acid precursor is added, and the remaining raw materials and steps are the same as those of Example 1.

[0054] Comparative Example 3

[0055] This comparative example is compared with Example 1, except that no alkyl glucoside is added to the synergist, and the remaining raw materials and steps are the same as those of Example 1.

[0056] Comparative Example 4

[0057] This comparative example is compared with Example 1, except that no sophorolipid is added in the synergist, and the remaining raw materials and steps are the same as those in Example 1.

[0058] Comparative Example 5

[0059] This comparative example is compared with Example 1, except that no synergist is added, and the remaining raw materials and steps are the same as those in Example 1.

[0060] Performance test

[0061] Test method:

[0062] The performance of the repair agents of Examples 1-3 and Comparative Examples 1-5 was tested.

[0063] The total amount of Cr(VI) in the soil was detected according to HJ 687-2014 "Determination of Cr(VI) in soil by alkali digestion / flame atomic absorption spectrophotometry"; the leaching amount of Cr(VI) in the soil was detected according to HJ / T 299-2007 "Solid waste leaching toxicity leaching method-sulfuric acid and nitric acid method".

[0064] Table 1 Total amount and leaching amount of Cr(VI) in soil before and after repair

[0065]

[0066] Note: O represents organic acid, P represents propylene glycol alginate, A represents sophorolipid, B represents alkyl glucoside, F represents iron-based material, and S represents sulfur-based material.

[0067] As can be seen from the data in Table 1, the total amount of Cr(VI) in the original soil before repair was 741 mg / kg, and the leaching amount was 22.2 mg / L, far exceeding the screening value of the second type of land (5.7 mg / kg) in "Soil Environmental Quality for Construction Land Soil Pollution Risk Control Standard (Trial)" (GB 36600-2018) and the maximum allowable discharge concentration of Cr(VI) of the first type of pollutant (0.5 mg / L) in "Integrated Wastewater Discharge Standard" (GB 8978-1996). After treatment with the repair agents of Examples 1-3, the total amount of Cr(VI) in the soil was 2.4 mg / kg, 2.7 mg / kg and 2.9 mg / kg, respectively, and the leaching amount of Cr(VI) in the soil was 0.07 mg / L, 0.10 mg / L and 0.12 mg / L, respectively, so that the total amount and leaching amount of Cr(VI) in the soil after repair can meet and are far below the relevant national standards.

[0068] In addition, compared with Example 1, the total amount of Cr(VI) in the soil and the leaching amount after the soil is treated by the repair agent of Comparative Examples 1-2 changing the acidic precursor and Comparative Examples 3-5 changing the synergist component are much higher than Example 1, and even the multiple data are higher than the national standard. It is shown that the repair agent of the present application greatly promotes the reduction efficiency of the reducing agent due to the addition of the acidic precursor and the synergist, and the repair agent changing the acidic precursor component or the synergist component is weak.

[0069] It should be noted that the above examples are only part of the preferred modes of implementing the present application, but not all. Obviously, based on the above examples of the present application, all other examples obtained by those skilled in the art without creative labor should belong to the scope of protection of the present application.

Claims

1. A remediation agent for high concentration of hexavalent chromium contaminated soil, characterized by, The remediation agent comprises the following amounts of raw materials: 2.8-6g of the acid precursor, 4-6g of the iron-sulfur reducing agent, and 1-2g of the synergistic agent; the acid precursor comprises organic acid and propylene glycol alginate; the iron-sulfur reducing agent comprises iron-based material and sulfur-based material; the synergistic agent comprises sophorose lipids and alkyl glucoside; The organic acid is one or more of oxalic acid, citric acid, and tartaric acid; The iron-based material is one or more of ferrous sulfate, ferrous chloride, and zero-valent iron; The sulfur-based material is one or more of sodium thiosulfate, sodium metabisulfite, and calcium polysulfide; The mass ratio of the organic acid to the propylene glycol alginate is (2.5-5):1; The mass ratio of the iron-based material to the sulfur-based material is 4:

1.

2. The remediation agent for high concentration of hexavalent chromium contaminated soil according to claim 1, characterized by, The mass ratio of sophorose lipids to alkyl glucoside in the synergistic agent is 1:

1.

3. A method for preparing the remediation agent against the soil contaminated with high concentration of hexavalent chromium according to any one of claims 1-2, characterized in that, The method comprises the following steps: S1: organic acid powder is added to 50ml ultrapure water, and after ultrasonic dissolution in an oxygen-free or low-oxygen environment, an organic acid liquid is obtained, which is stored at ≤20℃ for standby use; after the addition of propylene glycol alginate to the above-mentioned organic acid liquid, the volume is adjusted to 100ml with ultrapure water, and the mixture is uniformly mixed to obtain an acid precursor colloidal solution; S2: sophorose lipids and alkyl glucoside are added to 20ml ultrapure water and fully dissolved to obtain a synergistic agent solution; S3: after the removal of free water from the iron-based material, the dried iron-based material and the sulfur-based material are uniformly mixed, ground to 50-100 mesh, and then an iron-sulfur reducing agent is obtained.

4. A method for remediation of the remediation agent for the soil contaminated with high concentration of hexavalent chromium according to any one of claims 1 to 2, characterized in that, The method comprises the following steps: The wind-dried contaminated soil is taken, the acid precursor colloidal solution and the synergistic agent solution are added, and the mixture is stirred and reacted for 2-4h, then the iron-sulfur reducing agent is added, the mixture is stirred for 15-30min, and then the mixture is left to stand and cure for 3-5 days.

5. The method for remediation according to claim 4, wherein the remediation agent is used for the remediation of soil contaminated with high concentrations of hexavalent chromium. The contaminated soil is sieved to 10 mesh.

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