Remediation agent for high-concentration hexavalent chromium contaminated soil and preparation method and remediation method thereof

Abstract

The invention discloses a remediation agent for high-concentration hexavalent chromium polluted soil and a preparation method and a remediation method thereof, and belongs to the technical field of soil pollution remediation. The remediation agent for the high-concentration hexavalent chromium contaminated soil comprises an acidic precursor, an iron-sulfur reducing agent and a synergist, the acidic precursor comprises organic acid and propylene glycol alginate; the iron-sulfur reducing agent comprises an iron-based reducing agent and a sulfur-based reducing agent; the synergist is prepared from sophorolipid and alkyl glucoside. The remediation agent can be used for high-concentration hexavalent chromium contaminated soil, hexavalent chromium in the soil is exposed in a Cr < 6 + > ion form as much as possible by replacing the hexavalent chromium in the soil, then the hexavalent chromium is converted into trivalent chromium by using a reducing agent, and the removal efficiency of the hexavalent chromium reaches up to 99.6%. In addition, the soil remediation agent is simple in use mode, rapid and thorough in reaction and lasting in effect.

Description

Technical Field

[0001] The present invention belongs to the technical field of soil pollution remediation, and in particular relates to a remediation agent for soil contaminated with high concentration of hexavalent chromium, and a preparation method and a remediation method thereof. Background Art

[0002] Chromium is an important strategic metal resource with a wide range of applications, including metallurgy, pigments, leather tanning, wood preservation, electroplating, medicine, organic synthesis, dyes, chemicals, ceramics, glass, oil extraction, printing plate making, catalysts, magnetic materials, metal corrosion inhibition, metal polishing and other process flows. It is related to 15% of my country's commodity varieties and is irreplaceable.

[0003] Chromium chemicals, leather making and electroplating are the main chromium-related industries, and they are also accompanied by serious chromium-contaminated soil problems.

[0004] At present, the remediation technology of chromium-contaminated soil is mainly based on the principle of reduction and stabilization of hexavalent chromium, including chemical reduction, chemical leaching, electrodynamic remediation and biological remediation technology. Considering the technical applicability and economy, most of the chromium-contaminated soil remediation projects still use chemical reduction remediation technology. The chemical reduction method mainly converts highly toxic Cr(VI) into low-toxic and difficult-to-migrate Cr(III) precipitates through a reduction reaction. Commonly used reducing agents include FeSO4, FeO, calcium polysulfide and reducing microorganisms. This method can effectively reduce the migration ability and biological utilization ability of chromium. For example, Chinese patent CN 110079321A discloses a method for preparing and using a hexavalent chromium-contaminated soil remediation agent. The maximum concentration of Cr(VI) in the original soil is 2500 mg / kg, and the Cr(III) after repair is 2500 mg / kg. 6+ Although the leaching concentration is lower than 0.1 mg / L, the total amount of Cr(VI) repaired is not taken into account. Chinese patent CN110302746 A discloses a composite material for the repair of hexavalent chromium contaminated water or soil and its preparation method. Adding 5% of the composite material can reduce the total amount of hexavalent chromium in the soil from about 424 mg / kg to about 39 mg / kg, but the total amount of hexavalent chromium after repair is still 13 times the screening value of the first category of land use in GB 36600.

[0005] Therefore, there is an urgent need to develop a remediation agent to deal with the 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 of the invention

[0006] In view of the problems and defects of existing hexavalent chromium repair materials, the present invention provides a repair agent for soil contaminated with high concentration of hexavalent chromium, a preparation method thereof and a repair method thereof.

[0007] In order to achieve the above technical objectives, the technical solution adopted by the present invention is:

[0008] A repair agent for soil contaminated with high concentration of hexavalent chromium. Taking 100g of hexavalent chromium contaminated soil as an example, the repair agent includes the following raw materials: 2.8-6g of acidic precursor, 4-6g of iron-sulfur reducing agent, and 1-2g of synergist; the acidic precursor includes organic acid and propylene glycol alginate; the iron-sulfur reducing agent includes iron-based materials and sulfur-based materials; the synergist includes sophorolipids and alkyl glucoside.

[0009] Furthermore, 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 pyrosulfite, and calcium polysulfide.

[0010] Furthermore, the mass ratio of sophorolipids to alkyl glucoside in the synergist is 1:1.

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

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

[0013] A method for preparing a repair agent for soil contaminated with high concentration of hexavalent chromium, comprising the following steps:

[0014] S1: Add organic acid powder to 50 ml ultrapure water, dissolve it by ultrasonic in an anaerobic or hypoxic environment to obtain an organic acid liquid, and store it at ≤20°C for standby use; add propylene glycol alginate to the organic acid liquid, and then add ultrapure water to make the volume to 100 ml, mix well to obtain an acid precursor colloidal solution, and pack it into the warehouse;

[0015] S2: Add sophorolipids and alkyl glucoside into 20 ml ultrapure water and fully dissolve to obtain a synergist solution, which is then divided into containers and stored;

[0016] S3: After drying the iron-based material to remove free water, the dried iron-based material and sulfur-based material are evenly mixed, ground to 50-100 meshes to obtain an iron-sulfur reducing agent, which is packaged and stored.

[0017] A method for repairing soil contaminated with high-concentration hexavalent chromium using a repair agent, comprising the following steps:

[0018] Take the air-dried contaminated soil, add the acid precursor colloidal solution and the synergist solution, stir and react for 2-4 hours, add the iron-sulfur reducing agent, stir for 15-30 minutes, and let it stand for 3-5 days.

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

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

[0021] The soil remediation agent provided by the invention reduces the total amount of hexavalent chromium in the soil by reducing the highly toxic hexavalent chromium in the soil into low-toxic trivalent chromium.

[0022] The acidic precursor of the present invention comprises an organic acid and propylene glycol alginate. When the organic acid is added to a soil solution containing a calcium chromate solid solution, the organic acid will combine with calcium ions in the solution to generate calcium salt precipitation. As the calcium ion content in the solution decreases, in order to keep the precipitation equilibrium constant Ksp of calcium chromate in the solution unchanged, chromate ions will precipitate again, and propylene glycol alginate can prevent the regeneration of calcium chromate precipitation. At this time, a reducing agent is added to reduce the exposed Cr 6+ Reduction to Cr 3+ , and keep the soil in a reducing environment to avoid "yellowing".

[0023] The synergist is composed of sophorolipids and alkyl glucoside. Sophorolipids are a kind of biosurfactant, and alkyl glucoside is a kind of non-ionic surfactant. The combination of the two shows a significant effect in soil remediation. On the one hand, it reduces the surface tension of water, enhances the penetration of acidic precursors into the soil, and accelerates the adsorption of Cr on soil particles. 6+ On the other hand, the synergist added in the present invention can increase the solubility of chromate ions, making it easier to expose the chromate ions of calcium chromate solidified in 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] Beneficial Effects

[0025] The repair agent and repair method are mainly used in soil contaminated with high concentration of hexavalent chromium, solving the problem that the hexavalent chromium solidified in soil particles cannot be reduced by only applying a reducing agent. The composition and method of the present invention can remove hexavalent chromium in the soil as much as possible, especially for soil rich in calcium chromate, the effect is more obvious. Compared with the treatment of extending the immersion time and increasing the number of immersion times, the technical solution of the present invention has a higher hexavalent chromium removal rate and a higher treatment efficiency.

[0026] The soil remediation agent provided by the present invention has the characteristics of simple addition method, rapid and thorough reaction and lasting effect, and is particularly suitable for soil contaminated with high concentration of hexavalent chromium. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a flow chart of the present invention. DETAILED DESCRIPTION

[0028] The technical solution of the present invention is further described below in conjunction with specific embodiments, but is not limited thereto.

[0029] Example 1

[0030] A method for preparing a repair agent for soil contaminated with high concentration of hexavalent chromium, comprising the following steps:

[0031] 5 g of oxalic acid powder is added to 50 ml of ultrapure water, and dissolved by ultrasonication in an anaerobic or hypoxic environment to obtain an organic acid liquid, which is stored at ≤20°C for later use; 1 g of propylene glycol alginate is added to the organic acid liquid, and then the volume is fixed to 100 ml with ultrapure water, and the mixture is mixed evenly to obtain an acidic precursor colloidal solution;

[0032] Add 1 g of sophorolipid and 1 g of alkyl glucoside into 20 ml of ultrapure water and fully dissolve to obtain a synergist solution;

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

[0034] A method for repairing soil contaminated with high-concentration hexavalent chromium using a repair agent, comprising the following steps:

[0035] Take 100g of contaminated soil that has been air-dried and passed through a 10-mesh nylon sieve, place it in a 500ml beaker, add the prepared acid precursor colloidal solution and synergist solution, stir and react for 4h, then add the prepared iron-sulfur reducing agent, stir for 30min, and let it stand for 5 days.

[0036] Example 2

[0037] A method for preparing a repair agent for soil contaminated with high concentration of hexavalent chromium, comprising the following steps:

[0038] 3 g of citric acid powder is added to 50 ml of ultrapure water, and after ultrasonic dissolution in an anaerobic or hypoxic environment, an organic acid liquid is obtained, which is stored at ≤ 20°C for later use; 0.6 g of propylene glycol alginate is added to the organic acid liquid, and then the volume is fixed to 100 ml with ultrapure water, and the mixture is mixed evenly to obtain an acidic precursor colloidal solution;

[0039] Add 0.5 g of sophorolipid and 0.5 g of alkyl glucoside into 20 ml of ultrapure water and fully dissolve to obtain a synergist solution;

[0040] After the ferrous sulfate is dried and free water is removed, 2g of the dried ferrous chloride and 1g of sodium pyrosulfite are mixed evenly, and ground into 50-100 meshes to obtain an iron-sulfur reducing agent.

[0041] A method for repairing soil contaminated with high-concentration hexavalent chromium using a repair agent, comprising the following steps:

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

[0043] Example 3

[0044] A method for preparing a repair agent for soil contaminated with high concentration of hexavalent chromium, comprising the following steps:

[0045] 2 g of tartaric acid powder is added to 50 ml of ultrapure water, and dissolved by ultrasonication in an anaerobic or hypoxic environment to obtain an organic acid liquid, which is stored at ≤ 20°C for later use; 0.8 g of propylene glycol alginate is added to the organic acid liquid, and then the volume is fixed to 100 ml with ultrapure water, and mixed evenly to obtain an acidic precursor colloidal solution;

[0046] Add 0.5 g of sophorolipid and 0.5 g of alkyl glucoside into 20 ml of ultrapure water and fully dissolve to obtain a synergist solution;

[0047] After the ferrous sulfate is dried and free water is removed, 3 g of the dried zero-valent iron and 1 g of calcium polysulfide are evenly mixed and ground into 50-100 meshes to obtain an iron-sulfur reducing agent.

[0048] A method for repairing soil contaminated with high-concentration hexavalent chromium using a repair agent, comprising the following steps:

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

[0050] Comparative Example 1

[0051] Compared with Example 1, this comparative example is the same as Example 1 except that propylene glycol alginate is not added to the acidic precursor. The other raw materials and steps are the same as those of Example 1.

[0052] Comparative Example 2

[0053] Compared with Example 1, this comparative example is the same as Example 1 except that the acidic precursor is not added. The other raw materials and steps are the same as Example 1.

[0054] Comparative Example 3

[0055] Compared with Example 1, this comparative example is the same as Example 1 except that alkyl glucoside is not added to the synergist, and the other raw materials and steps are the same as those of Example 1.

[0056] Comparative Example 4

[0057] Compared with Example 1, this comparative example is the same as Example 1 except that sophorolipid is not added to the synergist, and the other raw materials and steps are the same as those of Example 1.

[0058] Comparative Example 5

[0059] Compared with Example 1, this comparative example has the same raw materials and steps as Example 1 except that no synergist is added.

[0060] Performance Testing

[0061] Test method:

[0062] The performance tests were performed on the repairing agents of Examples 1-3 and Comparative Examples 1-5.

[0063] The total amount of Cr(VⅠ) in the soil is tested according to HJ 687-2014 "Determination of hexavalent chromium in soil by alkaline digestion / flame atomic absorption spectrophotometry"; the leaching amount of Cr(VⅠ) in the soil is tested according to HJ / T 299-2007 "Toxicity leaching method for solid waste - sulfuric acid and nitric acid method".

[0064] Table 1 Total amount and leaching amount of hexavalent chromium in soil before and after remediation

[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] It can be seen from the data in Table 1 that the total amount of Cr (VⅠ) in the original soil before repair is 741 mg / kg, and the leaching amount is 22.2 mg / L, which far exceeds the second-class land screening value (5.7 mg / kg) of the "Soil Environmental Quality Construction Land Soil Pollution Risk Control Standard (Trial)" (GB36600-2018) and the maximum allowable emission concentration (0.5 mg / L) of the first-class pollutant hexavalent chromium in the "Comprehensive Sewage Discharge Standard" (GB 8978-1996). After being treated with the repair agent of Examples 1-3 of the present invention, the total amount of Cr (VⅠ) in the soil is 2.4 mg / kg, 2.7 mg / kg, and 2.9 mg / kg, respectively, and the leaching amount of Cr (VⅠ) in the soil is 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 lower than the relevant national standards.

[0068] In addition, compared with Example 1, after the soil was treated with the repair agents of Comparative Examples 1-2 with changed acidic precursors and Comparative Examples 3-5 with changed synergist components, the total amount of Cr(VI) and the leaching amount in the soil were much higher than those in Example 1, and even many groups of data were higher than the relevant national standards. This shows that the addition of the acidic precursor and the synergist greatly promoted the reduction efficiency of the reducing agent in the repair agent of the present invention, while the repair agent with changed acidic precursor components or changed synergist components was weak in effect without one of them.

[0069] It should be noted that the above embodiments are only partial embodiments of the preferred methods of implementing the present invention, rather than all embodiments. Obviously, based on the above embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

Claims

1. A remediation agent for soil contaminated with high concentration of hexavalent chromium, characterized in that: Taking 100g of hexavalent chromium contaminated soil as an example, the remediation agent includes the following raw materials: 2.8-6g of acid precursor, 4-6g of iron-sulfur reducing agent, and 1-2g of synergist; the acid precursor includes organic acid and propylene glycol alginate; the iron-sulfur reducing agent includes iron-based materials and sulfur-based materials; The synergists include sophorolipids and alkyl glucosides.

2. The repair agent for high-concentration hexavalent chromium contaminated soil according to claim 1, characterized in that: 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 pyrosulfite, and calcium polysulfide.

3. The repair agent for soil contaminated with high concentration of hexavalent chromium according to claim 1, characterized in that: The mass ratio of sophorolipid to alkyl glucoside in the synergist is 1:

1.

4. The method for preparing a repair agent for soil contaminated with high concentration of hexavalent chromium according to claim 1, characterized in that: The mass ratio of the organic acid to propylene glycol alginate is (2.5-5):

1.

5. The method for preparing a repair agent for soil contaminated with high concentration of hexavalent chromium according to claim 1, characterized in that: The mass ratio of the iron-based material to the sulfur-based material is 4:

1.

6. A method for preparing a repair agent for soil contaminated with high concentration of hexavalent chromium according to any one of claims 1 to 5, characterized in that: The following steps are involved: S1: adding organic acid powder to 50 ml ultrapure water, dissolving it by ultrasonication in an anaerobic or hypoxic environment to obtain an organic acid liquid, and storing it at ≤20°C for later use; adding propylene glycol alginate to the organic acid liquid, and then adding ultrapure water to make the volume to 100 ml, and mixing well to obtain an acidic precursor colloidal solution; S2: Sophorolipids and alkyl glucoside are added into 20 ml ultrapure water and fully dissolved to obtain a synergist solution; S3: After drying the iron-based material to remove free water, the dried iron-based material and the sulfur-based material are evenly mixed and ground to 50-100 meshes to obtain an iron-sulfur reducing agent.

7. A method for repairing soil contaminated with high concentration hexavalent chromium using a repair agent according to any one of claims 1 to 5, characterized in that: The following steps are involved: Take the air-dried contaminated soil, add the acid precursor colloidal solution and the synergist solution, stir and react for 2-4 hours, add the iron-sulfur reducing agent, stir for 15-30 minutes, and let it stand for 3-5 days.

8. The method for repairing soil contaminated with high concentration hexavalent chromium according to claim 7, characterized in that: The contaminated soil was sieved to 10 mesh.

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