Green low-carbon treatment method for cyanide and hexavalent chromium combined polluted soil

Abstract

The invention discloses a green low-carbon treatment method for cyanide and hexavalent chromium combined polluted soil. The treatment method comprises the following steps: 1) screening and crushing the cyanide and hexavalent chromium combined polluted soil, so that the particle size of the crushed soil is less than or equal to 5cm; 2) mixing the screened cyanide and hexavalent chromium compound polluted soil with a sodium thiosulfate compound agent, treating, and carrying out first maintenance, wherein the compound agent comprises sodium thiosulfate pentahydrate and sodium dihydrogen phosphate; and (3) mixing the cyanide and hexavalent chromium combined polluted soil subjected to the first maintenance with sodium hydroxide to adjust the pH value, then carrying out second maintenance, and after the maintenance is completed, carrying out remediation effect evaluation until pollutants in the soil reach the standard. The method is suitable for various cyanide and hexavalent chromium combined contaminated soil, the physical and chemical properties of the contaminated soil are stable after treatment, and the subsequent environmental consumption risk is greatly reduced. Meanwhile, compared with a traditional repairing process, the carbon emission in the treatment process is remarkably reduced, and the method has the advantages of being environmentally friendly and low in carbon.

Description

Technical Field

[0001] The present invention belongs to the technical field of environmental protection, and more specifically, relates to a green and low-carbon treatment method for soil contaminated by cyanide and hexavalent chromium. Background Art

[0002] Cyanide is widely used in industrial production fields such as electroplating and metallurgy. Its long-term production and application will cause certain pollution to the soil environment. At the same time, in the industrial activities of electroplating, metallurgy and other industries, heavy metals such as hexavalent chromium may also enter the soil with cyanide, causing heavy metal pollution in the soil. Since cyanide and hexavalent chromium are widely used in electroplating, metallurgy and other industrial fields, the long-term production process in industrial parks can easily cause the soil to suffer from the combination of cyanide and hexavalent chromium. In the site survey of retired industrial sites, it was found that the combined pollution of cyanide and hexavalent chromium in the soil of industrial sites is common.

[0003] Cyanide is highly toxic to the human body. 100 mg of sodium cyanide can kill a person. Hexavalent chromium enters the human body through the skin, mucous membranes or inhalation of dust, and will accumulate in the body, eventually causing a variety of health problems, including various cancers, and adversely affecting the blood system, kidneys and respiratory systems.

[0004] Industrial sites contaminated by cyanide and hexavalent chromium need to be repaired and treated for pollutants before they are redeveloped after retirement, and the next step of development and utilization can only be carried out after the land use requirements are met. At the same time, the most commonly used cement kiln co-disposal method has a large carbon emission, and under the current trend of energy conservation and emission reduction requirements, it has gradually failed to meet the needs of green and low-carbon repair and disposal. Therefore, it is urgent to provide a simple, efficient, green and low-carbon method to treat soil contaminated by cyanide and hexavalent chromium. Summary of the invention

[0005] The present invention aims to provide a green and low-carbon treatment method for soil contaminated by cyanide and hexavalent chromium. The present invention intends to detoxify and stabilize the soil contaminated by cyanide and hexavalent chromium, reasonably select treatment agents and treatment methods, and finally obtain a method and process for guiding the treatment construction of soil contaminated by cyanide and hexavalent chromium, thereby ensuring the restoration effect and providing convenience for subsequent risk control.

[0006] In order to achieve the above object, the present invention provides a method for treating soil contaminated by cyanide and hexavalent chromium, the method comprising:

[0007] 1) Crush the soil contaminated by cyanide and hexavalent chromium to a particle size of ≤5 cm;

[0008] 2) mixing the crushed cyanide and hexavalent chromium composite contaminated soil with a sodium thiosulfate compound agent for treatment, adjusting the soil moisture content and performing a first curing, wherein the sodium thiosulfate compound agent includes sodium thiosulfate pentahydrate and sodium dihydrogen phosphate;

[0009] 3) Mixing the cyanide and hexavalent chromium composite contaminated soil after the first curing with a stabilizer for disposal and performing a second curing, wherein the stabilizer is a sodium hydroxide solution.

[0010] As a preferred solution, in step 2), the moisture content of the soil contaminated by cyanide and hexavalent chromium after adjustment is 30%.

[0011] According to the present invention, after stabilization treatment, trivalent chromium and sodium thiocyanate pollutants in the soil are further stabilized, and the yellowing phenomenon of hexavalent chromium in the soil is less likely to occur, which facilitates subsequent long-term management and control.

[0012] As a preferred solution, in step 2), the amount of sodium thiosulfate pentahydrate added is 3.5-4.5% and the amount of sodium dihydrogen phosphate added is 0.8-1% relative to the total mass of the soil contaminated by cyanide and hexavalent chromium, thereby achieving the effects of cyanide detoxification and hexavalent chromium stable reduction.

[0013] As a preferred embodiment, in step 2), the first curing time is 7 days.

[0014] As a preferred embodiment, the mass percentage concentration of the sodium hydroxide solution is 30%. In step 3), the amount of sodium hydroxide solution added varies according to the total mass of the composite contaminated soil. Preferably, the amount added is such that the pH of the composite contaminated soil after adding the stabilizer is controlled at 8-9.

[0015] As a preferred embodiment, in step 3), the second curing time is 7 days.

[0016] As a preferred embodiment, both the first curing and the second curing are performed by coating.

[0017] As a preferred embodiment, in step 1), the cyanide concentration of the soil contaminated by cyanide and hexavalent chromium is ≤89.35 mg / kg, and the hexavalent chromium concentration is ≤218 mg / L.

[0018] After step 3), the process also includes the step of evaluating and monitoring the effect of the soil after curing. The evaluation and monitoring is to detect the concentrations of cyanide and hexavalent chromium in the soil. If the detected concentrations are lower than the set values, the treatment of the composite contaminated soil is completed. Otherwise, the process returns to step 2 for remediation.

[0019] As a preferred solution, the present invention has the following effects and advantages compared with the prior art:

[0020] 1) The sodium thiosulfate compound used contains sodium thiosulfate (pentahydrate) and sodium dihydrogen phosphate. The cyanide in the soil combines with the sulfide ions and cyanide ions provided by sodium thiosulfate to generate low-toxic sodium thiocyanate, thereby reducing the toxicity of cyanide. On the other hand, sodium thiosulfate can reduce hexavalent chromium in the soil to low-toxic trivalent chromium, thereby achieving the purpose of repair.

[0021] S 2 O 3 2- +CN - →SO 3 2- +SCN -

[0022] Cr 2 O 7 2- +14H + +6S 2 O 3 2- →2Cr 3+ +7H 2 O+3S 4 O 6 2-

[0023] At the same time, sodium dihydrogen phosphate is added according to the characteristics of trivalent chromium. Phosphate has the function of stabilizing trivalent chromium. After hexavalent chromium is reduced to trivalent chromium by sodium thiosulfate, part of the trivalent chromium ions exist as amorphous trivalent chromium. Using sodium dihydrogen phosphate as a stabilizer can convert amorphous trivalent chromium into insoluble CrPO 4 Crystals are less affected by pH value, which can further improve the stability of trivalent chromium in the soil, reduce the amount of repair agents added, and ensure the long-term repair effect.

[0024] 2) Since soil pH is unstable, adding sodium hydroxide after the first step of dosing treatment of soil contaminated by cyanide and hexavalent chromium can keep the soil in alkaline conditions. On the one hand, it can increase the stability of trivalent chromium in the soil after repair and reduce the migration and penetration of chromium to the external environment; on the other hand, under alkaline conditions, sodium thiocyanate can also exist more stably, reducing the environmental risk of subsequent absorption of the soil after repair.

[0025] 3) The present invention is applicable to the remediation of soil contaminated by cyanide and hexavalent chromium. After treatment, the physical and chemical properties of the contaminated soil are stabilized, which greatly reduces the environmental risks of subsequent disposal.

[0026] 4) To handle 10000m 3 The contaminated soil was simulated and calculated according to the carbon emission factor method. The carbon emission of the contaminated soil treated by the treatment method selected in the present invention is 11.55t / m 3, and the commonly used repair method of cement kiln co-disposal (carbon emissions are 376.49t / m 3 ), wet detoxification + stabilization treatment (carbon emissions are 37.05t / m 3 ) compared with other technologies, it has the characteristics of being green and low-carbon.

[0027] Other features and advantages of the present invention will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 A flow chart of a method for treating soil contaminated by cyanide and hexavalent chromium according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0029] The preferred embodiments of the present invention will be described in more detail below. Although the preferred embodiments of the present invention are described below, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to make the present invention more thorough and complete, and to fully convey the scope of the present invention to those skilled in the art.

[0030] Figure 1 The flowchart of the method for treating soil contaminated by cyanide and hexavalent chromium according to one embodiment of the present invention is shown. Figure 1 As shown, the soil contaminated by cyanide and hexavalent chromium is first excavated and transported, then crushed and screened, and then sodium thiosulfate compound agent is added to the crushed and screened soil for the first curing, and then sodium hydroxide is added for the second curing, and the effect evaluation and monitoring are carried out. If the standard is met (the concentrations of cyanide and hexavalent chromium in the soil are lower than the set value, for example, lower than the first category of land screening value requirements in the Soil Environmental Quality Construction Land Soil Pollution Risk Control Standard (Trial) (GB36600-2018)), the remediation is terminated. If the standard is not met, the agent addition and other steps are performed again.

[0031] Example 1

[0032] Example 1 The selected soil sample had a cyanide concentration of 89.35 mg / kg, a hexavalent chromium concentration of 218 mg / kg, a soil pH of 7.86, and a moisture content of about 22%. About 10 tons of contaminated soil was excavated and transported to the disposal site by sealed vehicles. The contaminated soil was crushed using an ALLU crushing and screening bucket, and the soil particle size after crushing was ≤5 cm; the ALLU crushing and screening bucket was used to mix the contaminated soil after screening and crushing with 4.5% of the soil mass of sodium thiosulfate pentahydrate and 1% of sodium dihydrogen phosphate, and water was added to the soil to adjust the soil moisture content to 30%. After three stirrings to fully mix the agent and the soil, cover and maintain under natural conditions for 7 days; after the maintenance is completed, spray 1% of the soil mass of sodium hydroxide solution (concentration 30%) evenly into the soil and use the ALLU crushing and screening bucket to fully mix again until the soil pH stabilizes at 8-9. After fully mixing, cover and maintain under natural conditions for 7 days; the soil cyanide concentration of the soil after the repair was measured to be 1.23 mg / kg, the hexavalent chromium concentration was 0.53 mg / kg, and the pH was 8.23, which met the first category of land screening value requirements in the "Soil Environmental Quality Construction Land Soil Pollution Risk Control Standard (Trial)" (GB36600-2018).

[0033] Example 2

[0034] Example 2 The selected soil sample had a cyanide concentration of 43.46 mg / kg, a hexavalent chromium concentration of 82.12 mg / kg, a soil pH of 7.57, and a moisture content of about 21%. About 10 tons of contaminated soil was excavated and transported to the disposal site by sealed vehicles. The contaminated soil was crushed using an ALLU crushing and screening bucket, and the soil particle size after crushing was ≤5 cm; the ALLU crushing and screening bucket was used to mix the contaminated soil after screening and crushing with 4% of the soil mass of sodium thiosulfate pentahydrate and 1% of sodium dihydrogen phosphate, and water was added to the soil to adjust the soil moisture content to 30%. After three stirrings to fully mix the agent and the soil, cover and maintain under natural conditions for 7 days; after the maintenance is completed, spray 1% of the soil mass of sodium hydroxide solution (concentration 30%) evenly into the soil and use the ALLU crushing and screening bucket to fully mix again until the soil pH stabilizes at 8-9. After fully mixing, cover and maintain under natural conditions for 7 days; the soil cyanide concentration of the soil after the repair was measured to be 1.02 mg / kg, the hexavalent chromium concentration was 1.63 mg / kg, and the pH was 8.01, which met the first category of land screening value requirements in the "Soil Environmental Quality Construction Land Soil Pollution Risk Control Standard (Trial)" (GB36600-2018).

[0035] Example 3

[0036] Example 3 The cyanide concentration of the selected soil sample was 23.12 mg / kg, the hexavalent chromium concentration was 24.01 mg / kg, the soil pH was 7.53, and the moisture content was about 23%. About 10 tons of contaminated soil was excavated and transported to the disposal site by sealed vehicles. The contaminated soil was crushed using an ALLU crushing and screening bucket, and the soil particle size after crushing was ≤5 cm; the ALLU crushing and screening bucket was used to mix the contaminated soil after screening and crushing with 3.5% of the soil mass of sodium thiosulfate pentahydrate and 0.8% of sodium dihydrogen phosphate, and water was added to the soil to adjust the soil moisture content to 30%. After three stirrings to fully mix the agent and the soil, cover and maintain under natural conditions for 7 days; after the maintenance is completed, spray 1% of the soil mass of sodium hydroxide solution (concentration 30%) evenly into the soil and use the ALLU crushing and screening bucket to fully mix again until the soil pH stabilizes at 8-9. After fully mixing, cover and maintain under natural conditions for 7 days; after the repaired soil, no cyanide was detected, the hexavalent chromium concentration was 0.56 mg / kg, and the pH was 8.21, which met the first category of land screening value requirements in the "Soil Environmental Quality Construction Land Soil Pollution Risk Control Standard (Trial)" (GB36600-2018).

[0037] The above examples show that the method of the present invention can greatly reduce the index of pollutants in the soil contaminated by cyanide and hexavalent chromium. For the contaminated soil with cyanide concentration ≤89.35mg / kg and hexavalent chromium concentration ≤218mg / L, after one round of treatment by the method of the present invention, the first type of land use screening value requirements in the corresponding standard can be met, which proves the high efficiency of the method of the present invention. At the same time, the present invention reasonably selects the composition of the repair agent according to the characteristics of the pollutants, so that the amount of the repair agent added is small. At the same time, sodium hydroxide is added after the first step of the dosing treatment of the soil contaminated by cyanide and hexavalent chromium. On the one hand, it can increase the stability of trivalent chromium in the soil after repair and reduce the migration and penetration of chromium to the external environment; on the other hand, under alkaline conditions, sodium thiocyanate can also exist more stably, reducing the environmental risk of subsequent absorption of the soil after repair and ensuring the long-term nature of the repair effect.

[0038] Compared with the traditional treatment methods such as cement kiln co-treatment and landfill of hexavalent chromium and cyanide composite contaminated soil, the treatment method of the present invention has the characteristics of low carbon emission during the construction process and low secondary pollution risk. 3 The contaminated soil was simulated and calculated according to the carbon emission factor method. The carbon emission of the contaminated soil treated by the treatment method selected in the present invention is 11.55t / m 3 , and the commonly used repair method of cement kiln co-disposal (carbon emissions are 376.49t / m 3 ), wet detoxification + stabilization treatment (carbon emissions are 37.05t / m 3 ) compared with other technologies, it has the characteristics of being green and low-carbon.

[0039] The embodiments of the present invention have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A green and low-carbon treatment method for soil contaminated by cyanide and hexavalent chromium, characterized in that: include: 1) crushing the soil contaminated by cyanide and hexavalent chromium to make the soil particle size of the contaminated soil ≤5cm; 2) mixing the crushed pre-treated cyanide and hexavalent chromium composite contaminated soil with a sodium thiosulfate compound agent for mixed treatment and adding water to control the moisture content for a first curing, wherein the sodium thiosulfate compound agent includes sodium thiosulfate pentahydrate and sodium dihydrogen phosphate; 3) Mixing the cyanide and hexavalent chromium composite contaminated soil after the first curing with a stabilizer for stabilization treatment and performing a second curing, wherein the stabilizer is a sodium hydroxide solution.

2. The method for treating soil contaminated by cyanide and hexavalent chromium according to claim 1, wherein: In step 1), the crushing method is to use an ALLU crushing and screening bucket for crushing.

3. The method for treating soil contaminated by cyanide and hexavalent chromium according to claim 1, wherein: In step 2), relative to the total mass of the soil contaminated by cyanide and hexavalent chromium, the amount of sodium thiosulfate pentahydrate added is 3.5-4.5%, and the amount of sodium dihydrogen phosphate added is 0.8-1%.

4. The method for treating soil contaminated by cyanide and hexavalent chromium according to claim 1, wherein: In step 2), the soil moisture content is controlled to be 30% after adding water.

5. The method for treating soil contaminated by cyanide and hexavalent chromium according to claim 1, wherein: In step 2), the first curing period is 7 days.

6. The method for treating soil contaminated by cyanide and hexavalent chromium according to claim 1, wherein: In step 3), the mass percentage concentration of the sodium hydroxide solution is 30%, and the amount of the stabilizer added is such that the pH of the composite contaminated soil after adding the stabilizer is controlled at 8-9.

7. The method for treating soil contaminated by cyanide and hexavalent chromium according to claim 1, wherein: In step 3), the second curing period is 7 days.

8. The method for treating soil contaminated by cyanide and hexavalent chromium according to claim 1, wherein: The first curing and the second curing are both performed by coating.

9. The method for treating soil contaminated by cyanide and hexavalent chromium according to claim 1, wherein: In step 1), the cyanide concentration of the soil contaminated by cyanide and hexavalent chromium is ≤89.35 mg / kg, and the hexavalent chromium concentration is ≤218 mg / L.

10. The method for treating soil contaminated by cyanide and hexavalent chromium according to claim 1, further comprising the step of evaluating and monitoring the effect of the soil after curing after step 3), wherein the evaluation and monitoring of the effect is to detect the concentrations of cyanide and hexavalent chromium in the soil. If the detected concentrations are lower than the set values, the treatment of the composite contaminated soil is completed. Otherwise, the method returns to step 2) for remediation.

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