Remediation agent and method for remedying hexavalent chromium contaminated soil

Abstract

The invention discloses a repairing agent and method for repairing hexavalent chromium contaminated soil. The repairing agent is composed of pyroligneous liquor and ferrite, the addition amount of the ferrite in each milliliter of the pyroligneous liquor is 0.006-0.08 g, and the concentration of the pyroligneous liquor is 50-100%. The method comprises the following steps: adding a repairing agent into the chromium-contaminated soil, adding deionized water, uniformly stirring the soil, keeping the water content of the soil, standing and maintaining, reducing hexavalent chromium in the soil into trivalent chromium, and reducing and removing the hexavalent chromium in the chromium-contaminated soil. The method is high in hexavalent chromium removal efficiency, high in operability, good in practicability and high in applicability in strong alkaline soil.

Description

Technical Field

[0001] The present invention relates to the field of soil pollution control, and in particular to a repairing agent for repairing hexavalent chromium-contaminated soil and a method thereof. Background Art

[0002] Chromium salts are important industrial raw materials and chemical products, widely used in metallurgy, electroplating, building materials, leather, anti-corrosion, dyes and other industries. my country is the main country producing chromium salts, but due to the relatively backward production technology of early chromium salt plants, a large amount of chromium slag was produced in the process of producing chromium salts. The continuous leaching of chromium slag after stacking caused the chromium concentration in the surrounding soil to exceed the standard. At the same time, the high alkalinity of chromium slag will also cause the pH value of the soil to increase. Cr (VI) in the soil has the characteristics of high toxicity and strong mobility, which will cause great harm to the environment and human health.

[0003] At present, the commonly used remediation technologies for removing Cr(VI) pollutants from soil mainly include chemical reduction remediation technology, solidification / stabilization technology, electric remediation technology, leaching remediation technology, and bioremediation technology. Chemical reduction technology is currently the most widely used method for treating chromium-contaminated soil due to its wide applicability and low cost. Commonly used reducing agents include iron-based reducing agents (ferrous sulfate, ferrous chloride, etc.), sulfur-based reducing agents (calcium polysulfide and sodium thiosulfate, etc.) and organic reducing agents (organic acids, biochar, etc.). However, due to the strong alkalinity of chromium slag, the chromium-contaminated soil affected by chromium slag is generally an alkaline medium system dominated by Cr(VI), which results in the inability of Cr(VI) in the solid phase to fully dissolve and react with the reducing agent, and Cr(VI) reduction is a process that consumes H. + The reaction process, the restoration effect of reducing agents such as ferrous sulfate and sodium sulfite will be restricted by the soil pH. Patent CN109796984A discloses a reduction stabilization agent for chromium-contaminated soil, which directly reduces hexavalent chromium to trivalent chromium using calcium polysulfide and ferrous sulfate, but the aqueous solution of calcium polysulfide is strongly alkaline, which will damage the soil structure and its physical and chemical properties, and the generated hydrogen sulfide gas is toxic. Patent CN104307868A discloses a method for removing hexavalent chromium from chromium-contaminated soil, adding ferrous sulfate to reduce hexavalent chromium to trivalent chromium, but Cr(VI) cannot be fully dissolved and released to react with the agent, and the reduction effect of ferrous sulfate will be inhibited under strong alkaline conditions.

[0004] For weakly alkaline hexavalent chromium contaminated soil, generally, acid (sulfuric acid, hydrochloric acid, etc.) is used to neutralize the soil first, and then a general reducing agent is used for reduction. However, for highly alkaline chromium contaminated soil, not only is the alkalinity strong, but the alkalinity is also high, and a large amount of acid needs to be consumed for neutralization, which greatly increases the cost of repair. Patent CN103071670A discloses a method and equipment for detoxification of chromium slag contaminated soil, adding an acidic agent (98% concentrated sulfuric acid) and an auxiliary agent (ferrous sulfide) to dissolve the hexavalent chromium, and then adding ferrous sulfate with a content of 16% to 24% to control the pH 5 to 6.5 to reduce the hexavalent chromium to trivalent chromium, but when repairing a large area of ​​soil, a large amount of sulfuric acid needs to be consumed, and sulfuric acid reacts with calcium oxide in alkaline soil to generate slightly soluble calcium sulfate that crystallizes on the surface of soil particles to prevent acid and calcium oxide from continuing to react, which greatly increases the cost of repair. Patent CN105950165A discloses a chromium-contaminated soil remediation improver and a remediation method thereof, which uses an improver composed of 5% to 25% ferrous sulfate, 5% to 25% calcium polysulfide, 5% to 30% humic acid resin, 1% to 25% cow dung, and 1% to 25% fungus residue to repair the chromium in the soil. However, calcium polysulfide has strong alkalinity and requires more acid to neutralize it, which further increases the remediation cost and poses potential safety issues.

[0005] The use of organic reducing agents such as small molecule organic acids and biochar will not damage the soil structure and is green and environmentally friendly, but their main disadvantage as electron donors is that the reaction rate is slow and it takes a relatively long time to successfully repair. Therefore, it is urgent to develop a treatment method suitable for alkaline soil around chromium slag dumps with high hexavalent chromium removal efficiency. Summary of the invention

[0006] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a repair agent and method for repairing hexavalent chromium contaminated soil. The present invention utilizes biomass pyrolysis to prepare wood vinegar, which is prepared with ferrous salt to prepare a repair agent for repairing hexavalent chromium contaminated soil. The repair agent is applied to highly alkaline soil containing hexavalent chromium to reduce the hexavalent chromium in the soil to trivalent chromium. The repair agent of the present invention has low cost, high efficiency, strong operability and good practicality.

[0007] To achieve the above purpose, the technical solution designed by the present invention is as follows:

[0008] The invention provides a repairing agent for repairing hexavalent chromium-contaminated soil. The repairing agent consists of wood vinegar and ferrous salt, wherein the addition amount of the ferrous salt is 0.006-0.08 g per milliliter of the wood vinegar, and the concentration of the wood vinegar is 50-100%.

[0009] Furthermore, the ferrous salt is ferrous sulfate or ferrous sulfate heptahydrate.

[0010] Furthermore, the pH of the wood vinegar is 2.6, and the organic acid content is 12% (the main components of wood vinegar are acids, phenols, ketones and alcohols, and the acids are mainly acetic acid and propionic acid).

[0011] The present invention also provides a method for preparing the repair agent, comprising the following steps:

[0012] (1) washing the biomass raw material, drying it, and crushing it to obtain raw material powder;

[0013] (2) subjecting the raw material powder to high-temperature carbonization treatment under a nitrogen or inert gas atmosphere, and collecting condensate after cooling to obtain crude wood vinegar;

[0014] (3) allowing the crude wood vinegar to stand until stratification occurs, and extracting the clear liquid from the middle layer;

[0015] (4) adding activated carbon powder to the clarified liquid, mixing, stirring, standing, filtering, and obtaining wood vinegar;

[0016] (5) Mixing the wood vinegar and ferrous salts can obtain a repair agent for repairing hexavalent chromium-contaminated soil.

[0017] Furthermore, in step (1), the biomass raw material is bamboo scraps or cotton stalks; and the particle size of the raw material powder is 0.5 to 3 mm.

[0018] Furthermore, in the step (2), the heating rate during the high-temperature carbonization process is 10-20°C / min, the maximum temperature of the carbonization treatment is 250-350°C, and the maximum carbonization temperature is maintained for 1 hour.

[0019] Furthermore, in the step (4), the amount of activated carbon powder added is 3-5%, the mixture is stirred for 10 minutes, and allowed to stand for 72 hours.

[0020] The present invention also provides a method for repairing chromium-contaminated soil using the repair agent, comprising the following steps: adding the repair agent to the chromium-contaminated soil, adding deionized water at the same time, stirring the soil evenly, maintaining the soil moisture content, and standing for curing.

[0021] Furthermore, the chromium-contaminated soil is hexavalent chromium-contaminated soil, and the hexavalent chromium content in the soil is 20 to 50 mg / kg.

[0022] Furthermore, the amount of the repair agent added is 20 to 40% of the soil mass.

[0023] Furthermore, the soil moisture content is 40%, and the static curing time is 4 days.

[0024] Principle of the present invention:

[0025] (1) Bamboo scraps and cotton stalks have a high content of hemicellulose. The refined wood vinegar generated after high-temperature carbonization is rich in organic acids such as acetic acid and formic acid, as well as substances such as phenols, aldehydes and ketones. Functional groups such as hydroxyl and carboxyl make the pH of wood vinegar low. After adding, it can reduce the pH of the soil. At the same time, it can also dissolve soil minerals, leading to the release of encapsulated Cr(VI). Functional groups such as hydroxyl, aldehyde and carbonyl can reduce the Eh of the soil, making wood vinegar have the potential to reduce Cr(VI). In addition, the Fe contained in wood vinegar 3 + , Mn 2+ Plasma has catalytic properties and can promote the reduction of Cr(VI) by reducing substances such as small molecular organic acids in wood vinegar.

[0026] (2) Ferrous salts can reduce hexavalent chromium to trivalent chromium under acidic and neutral conditions with high reduction efficiency. The reaction equation is: Cr 6+ +3Fe 2+ +8H + =Cr 3+ +3Fe 3+ +4H2O.

[0027] (3) After wood vinegar is mixed with ferrous salt, the small molecular organic acid in the wood vinegar can form a complex with Fe(III), thereby forming a Fe(II) / Fe(III)-organic acid complex with a lower redox potential, which promotes the reaction of Fe(II) reducing Cr(VI).

[0028] Beneficial effects of the present invention:

[0029] The present invention uses a repair agent prepared by combining wood vinegar and ferrous salt to synergistically repair hexavalent chromium-contaminated soil. Through the complexation and reduction of wood vinegar and ferrous salt, hexavalent chromium in the soil is reduced to trivalent chromium, and the reduction efficiency of hexavalent chromium is high, and the applicability in strongly alkaline soil is strong. The present invention uses wood vinegar as the main treatment agent, reduces the cost of the agent, and expands the resource utilization of agricultural wastes such as bamboo scraps. DETAILED DESCRIPTION

[0030] The present invention is further described in detail below in conjunction with specific embodiments so that those skilled in the art can understand.

[0031] Example 1

[0032] Preparation of wood vinegar:

[0033] (1) washing and drying the biomass raw material bamboo chips, and crushing them into pieces with a size of 0.5 to 3 mm;

[0034] (2) subjecting the bamboo chips to high-temperature carbonization treatment in a nitrogen or inert gas atmosphere, wherein the heating rate during the high-temperature carbonization process is 10 to 20° C. / min, the maximum carbonization temperature is 250 to 350° C., the maximum carbonization temperature is maintained for 1 hour, and the condensate is collected to obtain a crude wood vinegar liquid;

[0035] (3) allowing the crude wood vinegar to stand until stratification occurs, and extracting the clear brown liquid from the middle layer;

[0036] (4) Add 3-5% by mass of activated carbon powder to the clear brown liquid, mix, stir for 10 minutes, let stand for 72 hours, filter, and obtain wood vinegar.

[0037] The pH value of the wood vinegar is 2.6, the organic acid content is 12%, and the main components are acids (mainly acetic acid and propionic acid), phenols, ketones and alcohols.

[0038] Example 2

[0039] Preparation of remediation agent 1 for remediating hexavalent chromium contaminated soil:

[0040] (1) Weigh 0.04 g of FeSO4·7H2O and 4 mL of the wood vinegar prepared in Example 1;

[0041] (2) Mix the wood vinegar and FeSO4·7H2O to obtain a repair agent 1.

[0042] Example 3

[0043] Preparation of remediation agent 2 for remediating hexavalent chromium contaminated soil:

[0044] (1) Weigh 0.1 g of FeSO4·7H2O and 4 mL of the wood vinegar prepared in Example 1;

[0045] (2) Mix the wood vinegar and FeSO4·7H2O to obtain repair agent 2.

[0046] Example 4

[0047] Preparation of remediation agent 3 for remediating hexavalent chromium contaminated soil:

[0048] (1) Weigh 0.04 g of FeSO4·7H2O and 2 mL of the wood vinegar prepared in Example 1;

[0049] (2) Mix the wood vinegar and FeSO4·7H2O to obtain the repair agent 3.

[0050] Example 5

[0051] Preparation of remediation agent 4 for remediating hexavalent chromium contaminated soil:

[0052] (1) Weigh 0.1 g of FeSO4·7H2O and 2 mL of the wood vinegar prepared in Example 1;

[0053] (2) Mix wood vinegar and FeSO4·7H2O to obtain repair agent 4.

[0054] Comparative Example 1

[0055] Preparation of common repair agent 1:

[0056] Ordinary repair agent 1 is only 2mL of wood vinegar.

[0057] Comparative Example 2

[0058] Preparation of common repair agent 2:

[0059] The ordinary repair agent 2 is only 4mL of wood vinegar.

[0060] Comparative Example 3

[0061] Preparation of common repair agent 3:

[0062] The common repair agent 3 is only 0.04g FeSO4·7H2O.

[0063] Comparative Example 4

[0064] Preparation of common repair agent 4:

[0065] The common repair agent 4 is only 0.1g FeSO4·7H2O.

[0066] Example 5

[0067] Hexavalent chromium contaminated soil remediation method:

[0068] The total chromium content of the chromium slag yard of a ferroalloy plant in Hunan is 2360 mg / kg, the hexavalent chromium content is 29.58 mg / kg, and the leaching concentration of hexavalent chromium is 1.039 mg / L.

[0069] The remediation agents 1 to 4 for remediating hexavalent chromium-contaminated soil of Examples 2 to 5 and the common remediation agents 1 to 4 of Comparative Examples 1 to 4 were used to remediate hexavalent chromium-contaminated soil.

[0070] (1) 10 g of hexavalent chromium contaminated soil was taken, and a composite agent (i.e., remediation agents 1 to 4 for remediating hexavalent chromium contaminated soil and common remediation agents 1 to 4) was added, and deionized water was added to control the moisture content to 40%.

[0071] (2) After stirring evenly and naturally curing for 4 days, the soil was taken out and the leaching concentration of Cr(VI) was measured.

[0072] The Cr(VI) leaching conditions of hexavalent chromium contaminated soil remediated by remediation agents 1 to 4 and common remediation agents 1 to 4 are shown in Table 1 .

[0073] Table 1 Soil Cr(VI) leaching

[0074] deal with Cr(VI) leaching concentration (mg / L) Cr(VI) leaching concentration reduction percentage (%) Example 1 0.031 97.0 Example 2 0.027 97.4 Example 3 0.107 89.7 Example 4 0.210 79.8 Comparative Example 1 0.805 22.5 Comparative Example 2 0.752 27.6 Comparative Example 3 0.747 28.1 Comparative Example 4 0.141 86.4

[0075] It can be concluded from Table 1 that the Cr(VI) leaching concentration of Example 2 is the lowest, which is 0.027 mg / L, and the Cr(VI) leaching concentration reduction percentage is 97.4%, so Example 2 is the optimal soil remediation solution.

[0076] Although the above embodiments have been described in detail, they are only a part of the embodiments of the present invention, not all of them. People can also obtain other embodiments based on this embodiment without creativity, and these embodiments all belong to the protection scope of the present invention.

Claims

1. A remediation agent for remediating hexavalent chromium contaminated soil, characterized in that: The repair agent consists of wood vinegar and ferrous salt, wherein the addition amount of ferrous salt is 0.006-0.08g per milliliter of wood vinegar, and the concentration of wood vinegar is 50-100%.

2. The repairing agent according to claim 1, characterized in that: The ferrous salt is ferrous sulfate or ferrous sulfate heptahydrate.

3. The repairing agent according to claim 1, characterized in that: The pH value of the wood vinegar is 2.6, and the organic acid content is 12%.

4. A method for preparing the repair agent as claimed in claim 1, characterized in that: The following steps are involved: (1) washing the biomass raw material, drying it, and crushing it to obtain raw material powder; (2) subjecting the raw material powder to high-temperature carbonization treatment under a nitrogen or inert gas atmosphere, and collecting condensate after cooling to obtain crude wood vinegar; (3) allowing the crude wood vinegar to stand until stratification occurs, and extracting the clear liquid from the middle layer; (4) adding activated carbon powder to the clarified liquid, mixing, stirring, standing, filtering, and obtaining wood vinegar; (5) Mixing the wood vinegar and ferrous salts can obtain a repair agent for repairing hexavalent chromium-contaminated soil.

5. The preparation method according to claim 4, characterized in that: In the step (1), the biomass raw material is bamboo scraps or cotton stalks; and the particle size of the raw material powder is 0.5 to 3 mm.

6. The preparation method according to claim 4, characterized in that: In the step (2), the heating rate during the high-temperature carbonization process is 10-20°C / min, the maximum temperature of the carbonization treatment is 250-350°C, and the maximum carbonization temperature is maintained for 1 hour.

7. The preparation method according to claim 4, characterized in that: In the step (4), the amount of activated carbon powder added is 3-5%, the mixture is mixed and stirred for 10 minutes, and allowed to stand for 72 hours.

8. A method for repairing chromium-contaminated soil using the repair agent as claimed in claim 1, characterized in that: The following steps are involved: Add remediation agent to the chromium-contaminated soil, add deionized water at the same time, stir the soil evenly, maintain the soil moisture content, and let it stand for curing.

9. The method according to claim 8, characterized in that: The chromium-contaminated soil is hexavalent chromium-contaminated soil, and the hexavalent chromium content in the soil is 20-50 mg / kg.

10. The method according to claim 8, characterized in that: The amount of repair agent added is 20-40% of the soil mass; the soil moisture content is 40%, and the static curing time is 4 days.