Method for repairing cyanide-heavy metal combined polluted soil

Abstract

The invention provides a remediation method for cyanide-heavy metal combined contaminated soil, and relates to the technical field of soil remediation. The remediation method comprises the following steps: firstly, oxidizing cyanide in the polluted soil by using a cyanide stabilizer, and meanwhile, stabilizing heavy metals released after oxidizing a metal cyanide complex; and then, further stabilizing non-cyanide complex-state heavy metals in the soil by using a heavy metal stabilizer and an alkaline activator. Moreover, the heavy metal stabilizer not only can stabilize original heavy metals in the polluted soil, but also can synergistically stabilize metal ions released by the heavy metal cyanogen complex due to cyanide oxidation; meanwhile, Fe < 2 + > and Fe < 3 + > contained in the heavy metal stabilizer can further stabilize ferricyanide complex and other cyanide not prone to oxidation to generate non-toxic ferricyanide with extremely stable properties, the toxicity of the cyanide in the soil is reduced, and the microbial activity is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of soil remediation, and in particular to a method for remediating soil contaminated by cyanide-heavy metal complex. Background Art

[0002] Gold production mostly uses cyanide gold extraction technology, and gold ores are often accompanied by polymetallic minerals. Therefore, gold industry soil pollution is mostly characterized by cyanide and heavy metal complex pollution. Stabilization technology is a relatively mature technology for the remediation of heavy metal contaminated soil. This technology adds stabilizing agents to the soil, and changes the existence form of heavy metals in the soil through physical and chemical effects, converting them from highly active forms (such as exchangeable forms, carbonate-bound forms) to less active forms (such as residual forms), thereby reducing the mobility and bioavailability of heavy metals. The main working principles of stabilizers are adsorption, precipitation, ion exchange, and redox.

[0003] At present, the main stabilization agents for heavy metal contaminated soil are lime, phosphate, sulfide, clay minerals, biochar, etc., but the above agents generally have problems such as affecting soil structure and microbial activity, causing secondary pollution, and high agent costs, and have no obvious removal effect on cyanide in the soil.

[0004] In the prior art, the patent with publication number CN108405599A discloses a method for remediating soil contaminated by heavy metals and cyanide. In this method, sodium persulfate and water are added to the contaminated soil after screening and crushing, and the soil is stored and cured for 3-7 days; then sodium sulfide solution and water are added to the soil that has been cured once. Among them, sodium persulfate plays a role in oxidizing cyanide in the soil, and sodium sulfide plays a role in reducing and solidifying heavy metals in the soil. However, the sodium persulfate used in this method can only oxidize cyanide that is easily released, and has a poor treatment effect on iron-cyanide complexes with relatively stable chemical properties. In addition, the sodium sulfide used in this method has the problem of releasing hydrogen sulfide to produce secondary pollution.

[0005] In view of this, it is necessary to design an improved method for remediation of cyanide-heavy metal composite contaminated soil to solve the above problems. Summary of the invention

[0006] In view of the defects of the above-mentioned prior art, the purpose of the present invention is to provide a method for remediating cyanide-heavy metal composite contaminated soil. The remediation method first uses a cyanide stabilizer to oxidize the cyanide in the contaminated soil, and at the same time stabilizes the heavy metals released after the oxidation of the metal cyanide complex; then, the heavy metal stabilizer and the alkaline activator further stabilize the non-cyanide complexed heavy metals in the soil. In addition, the heavy metal stabilizer can not only stabilize the original heavy metals in the contaminated soil, but also synergistically stabilize the metal ions released by the heavy metal cyanide complex due to the oxidation of cyanide. At the same time, the Fe contained in the heavy metal stabilizer 2+ , Fe 3+ It can further stabilize ferrocyanide and other non-oxidizable cyanides such as ferrocyanide complexes to generate non-toxic and extremely stable ferric ferrocyanide, thereby reducing the toxicity of cyanide in the soil and improving the activity of microorganisms.

[0007] This remediation method achieves the removal of cyanide in the soil and the rapid and effective stabilization of heavy metal pollutants, reducing the toxicity of pollutants. The materials used are economical and readily available, and will not produce secondary pollution. It is a soil remediation method that can quickly and efficiently treat cyanide and heavy metal pollution.

[0008] To achieve the above object, the present invention provides a method for remediating cyanide-heavy metal composite contaminated soil, comprising the following steps: S1, excavating the contaminated soil to be repaired, crushing and screening the contaminated soil, removing the slag with a particle size greater than 2 cm; after screening, evenly distributing the contaminated soil on the anti-seepage layer; S2, preparing a solution of cyanide stabilizer with water, spraying it directly on the contaminated soil treated in step S1 and mixing and stirring; then performing a curing for 1 to 3 days; The cyanide stabilizer includes an activator and an oxidant; the activator includes one or more of fulvic acid, humic acid, palmitic acid and their salts; the oxidant is one or more of hydrogen peroxide and calcium peroxide; S3, fully stirring the heavy metal stabilizer and the alkaline activator to obtain a mixture, and then directly adding the mixture to the soil obtained after the primary curing in step S2 and mixing and stirring; after sufficient mixing, adjusting the soil moisture content to 20% to 30%, and performing secondary curing for 3 to 7 days; The heavy metal stabilizer is one or more of polyferric sulfate, ferric chloride, ferrous sulfate, and ferrous citrate; The alkaline activator is one or more of lime, calcium oxide, calcium sulfate, carbide slag, and neutralization slag; S4, sampling and monitoring the soil treated in step S3, detecting the leaching toxicity of heavy metals and cyanide in the soil, and comparing it with the acceptance criteria to determine whether it meets the requirements; if it does, the repaired soil that meets the standards is obtained; if it does not meet the standards, repeat the above steps S1-S3 until it meets the acceptance criteria.

[0009] As a further improvement of the present invention, the mass ratio of the activator to the oxidant in the cyanide stabilizer is (0.05~0.1):(1~2).

[0010] As a further improvement of the present invention, in step S3, the mass ratio of the heavy metal stabilizer to the alkaline activator in the mixture is (1-2): (0.1-0.5).

[0011] As a further improvement of the present invention, in step S2, the cyanide stabilizer is added in an amount of 1% to 3% of the mass of the contaminated soil to be remediated.

[0012] As a further improvement of the present invention, in step S3, the addition ratio of the mixture is 1% to 10% of the mass of the soil to be repaired.

[0013] As a further improvement of the present invention, in step S2, the cyanide stabilizer is prepared into a solution with a mass percentage of 10% to 20% by water.

[0014] As a further improvement of the present invention, the mass ratio of the cyanide stabilizer, the heavy metal stabilizer and the alkaline activator is (1-2):(1-2):(0.1-0.5).

[0015] As a further improvement of the present invention, the pollutants in the cyanide-heavy metal composite contaminated soil are cyanide and one or more of the heavy metals As, Pb, Cu, Zn, Cd, Cr, and Mn.

[0016] The beneficial effects of the present invention are: The method for repairing cyanide-heavy metal composite contaminated soil of the present invention first uses a cyanide stabilizer to achieve oxidation of cyanide in the contaminated soil, and at the same time stabilizes the heavy metals released after the oxidation of the metal cyanide complex; then uses a heavy metal stabilizer and an alkaline activator to further stabilize the non-cyanide complexed heavy metals in the soil.

[0017] Specifically, in the present invention, the activator humic acid in the cyanide stabilizer is a macromolecular organic substance widely present in nature, and its molecular structure contains a large number of functional groups such as carboxyl (-COOH) and phenolic hydroxyl (-OH). Carboxyl groups can dissociate under certain conditions to release hydrogen ions (H⁺), and release easily releasable cyanide in the soil by adjusting the pH value. Its negative ion form (-COO⁻) can react with heavy metal cations (such as Pb) through ion exchange, complexation, etc. 2+ , Cu 2+ 、Cd 2+ Phenolic hydroxyl groups can also form complexes with heavy metal ions. This coordination effect increases the adsorption of heavy metals on the surface of humic acid and reduces the mobility of heavy metal ions. At the same time, humic acid can improve the soil environment, promote the formation of soil aggregate structure, reduce soil bulk density, increase soil nutrient content, and improve microbial activity.

[0018] The oxidants hydrogen peroxide and calcium peroxide in the cyanide stabilizer can oxidize free and complex cyanide into non-toxic carbon dioxide, ammonia and water without secondary pollution.

[0019] Heavy metal stabilizers can not only stabilize the original heavy metals in the soil, but also stabilize the metal ions released by heavy metal cyanide complexes due to cyanide oxidation. 2+ , Fe 3+ It can further stabilize ferrocyanide and other non-oxidizable cyanides such as ferrocyanide complexes to generate non-toxic and extremely stable ferric ferrocyanide, thereby reducing the toxicity of cyanide in the soil and improving the activity of microorganisms.

[0020] Alkaline activators such as lime, calcium oxide, calcium sulfate, carbide slag, neutralizing slag, etc. can neutralize the soil acidity caused by the addition of humic acid, hydrogen peroxide, ferrous salts, etc., adjust the soil pH value to an appropriate range, and create good conditions for subsequent stabilization reactions.

[0021] Cyanide stabilizer, heavy metal stabilizer and alkaline stimulator can work together to remove cyanide from the soil and quickly and effectively stabilize heavy metal pollutants, thereby reducing the toxicity of pollutants.

[0022] The materials used in the present invention are economical and readily available, and will not generate secondary pollution. The present invention is a soil remediation method that can quickly and efficiently coordinately treat cyanide and heavy metal pollution. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is the experimental diagram of Example 1.

[0024] Figure 2 This is a diagram showing the treatment effect of Example 1.

[0025] Figure 3 This is the experimental diagram of Example 2.

[0026] Figure 4 This is a diagram showing the treatment effect of Example 2. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0028] It should also be noted that, in order to avoid obscuring the present invention due to unnecessary details, only structures and / or processing steps closely related to the scheme of the present invention are shown in the drawings, while other details that are not closely related to the present invention are omitted.

[0029] In addition, it should be noted that the terms "comprises", "includes" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or apparatus that includes a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or apparatus.

[0030] Existing stabilization agents have problems such as affecting soil structure and microbial activity, causing secondary pollution, and high agent costs.

[0031] The present invention provides a method for repairing cyanide-heavy metal composite contaminated soil, comprising the following steps: S1, excavating the contaminated soil to be repaired, crushing and screening the contaminated soil, removing the slag with a particle size greater than 2 cm; after screening, evenly distributing the contaminated soil on the anti-seepage layer; The pollutants in cyanide-heavy metal composite contaminated soil are cyanide and one or more of the heavy metals As, Pb, Cu, Zn, Cd, Cr, and Mn.

[0032] S2, preparing a solution of cyanide stabilizer with water, spraying it directly on the contaminated soil treated in step S1 and mixing and stirring; then performing a curing for 1 to 3 days; The cyanide stabilizer includes an activator and an oxidant; the activator includes one or more of fulvic acid, black humic acid, palmitic acid and their salts; the oxidant is one or more of hydrogen peroxide and calcium peroxide; Among them, the mass ratio of activator to oxidant in the cyanide stabilizer is (0.05~0.1): (1~2).

[0033] Specifically, the cyanide stabilizer is prepared into a solution with a mass percentage of 10% to 20% with water.

[0034] The addition ratio of cyanide stabilizer is 1%~3% of the mass of the contaminated soil to be remediated.

[0035] S3, fully stirring the heavy metal stabilizer and the alkaline activator to obtain a mixture, and then directly adding the mixture to the soil obtained after the primary curing in step S2 and mixing and stirring; after sufficient mixing, adjusting the soil moisture content to 20% to 30%, and performing secondary curing for 3 to 7 days; Among them, the mass ratio of heavy metal stabilizer to alkaline activator in the mixture is (1~2): (0.1~0.5).

[0036] Among them, the mass ratio of cyanide stabilizer, heavy metal stabilizer and alkaline activator is (1~2):(1~2):(0.1~0.5).

[0037] The mixture is added in a ratio of 1% to 10% of the mass of the soil to be repaired.

[0038] The heavy metal stabilizer is one or more of polyferric sulfate, ferric chloride, ferrous sulfate, and ferrous citrate; The alkaline activator is one or more of lime, calcium oxide, calcium sulfate, carbide slag, and neutralization slag; S4, sampling and monitoring the soil treated in step S3, detecting the leaching toxicity of heavy metals and cyanide in the soil, and comparing it with the acceptance criteria to determine whether it meets the requirements; if it does, the repaired soil that meets the standards is obtained; if it does not meet the standards, repeat the above steps S1-S3 until it meets the acceptance criteria.

[0039] The following is a description of the method for remediating cyanide-heavy metal composite contaminated soil provided by the present invention in conjunction with specific examples. Unless otherwise specified, the raw materials and reagents in the examples of this application are purchased through commercial channels.

[0040] Example 1 See also Figure 1 As shown, this embodiment provides a method for remediating cyanide-heavy metal composite contaminated soil: The soil contaminated with cyanide and heavy metal arsenic from a gold smelting enterprise was selected as the sample for this implementation. The cyanide content was 157 mg / kg and the arsenic content was 379 mg / kg.

[0041] Cyanide stabilizer (weight ratio: 10% humic acid, 90% hydrogen peroxide) was prepared from water into a 20% solution; the cyanide stabilizer was added to the contaminated soil to be treated at a ratio of 2% of the sample mass, the mixture was stirred evenly, and the solution was allowed to stand for 3 days.

[0042] Then, the heavy metal stabilizer and alkaline activator (weight ratio: 66% ferrous sulfate, 34% lime) were mixed and stirred evenly, and added into the soil sample treated with cyanide stabilizer at a ratio of 8%. Water was sprayed to adjust the moisture content to 25%, and the soil was left to stand for 5 days for curing.

[0043] Figure 1 The experimental diagram of the three parallel experiments in Example 1. The sample was subjected to leaching experiment using the procedure of "Solid Waste Leaching Toxicity Leaching Method Sulfuric Acid and Nitric Acid Method" (HJ / T 299-2007) to obtain the leachate, and the concentrations of cyanide and arsenic in the leachate were detected. The experimental data of the three groups of experiments were averaged to obtain the results shown in Table 1 and Figure 2 shown.

[0044] Table 1 Pollutant leaching toxicity before and after soil stabilization It can be seen from Table 1 that the concentrations of cyanide and arsenic in the leachate are greatly reduced after the stabilization treatment of contaminated soil, which can meet the Class IV standard limit requirements in the "Groundwater Quality Standard" (GB / T 14848-2017).

[0045] Example 2 See also Figure 3 As shown, this embodiment provides a method for remediating cyanide-heavy metal composite contaminated soil: The cyanide and heavy metal complex contaminated soil from a gold and copper smelting enterprise was selected as the sample for this implementation. The cyanide content was 65 mg / kg, the arsenic content was 81 mg / kg, and the lead content was 623 mg / kg.

[0046] Cyanide stabilizer (weight ratio: 20% potassium fulvic acid, 80% calcium peroxide) was prepared from water into a 10% solution; the cyanide stabilizer was added to the sample at a ratio of 1% of the sample mass, the mixture was stirred evenly, and the solution was allowed to stand for 1 day.

[0047] Then, the heavy metal stabilizer and alkaline activator (weight ratio: 80% polyferric sulfate, 20% carbide slag) were mixed and stirred evenly, added into the soil sample treated with cyanide stabilizer at a ratio of 5%, sprayed with water, adjusted the moisture content to 30%, and allowed to stand for 3 days.

[0048] Figure 3 The experimental diagram of the three parallel experiments in Example 2. The sample was subjected to leaching experiment using the procedure of "Solid Waste Leaching Toxicity Leaching Method Sulfuric Acid and Nitric Acid Method" (HJ / T 299-2007) to obtain the leachate, and the concentrations of cyanide, arsenic and lead in the leachate were detected. The experimental data of the three groups of experiments were averaged to obtain the results shown in Table 2 and Figure 4 shown.

[0049] Table 2 Pollutant leaching toxicity before and after soil stabilization It can be seen from Table 2 that the concentrations of cyanide and arsenic in the leachate are greatly reduced after the stabilization treatment of contaminated soil, which can meet the Class IV standard limit requirements in the "Groundwater Quality Standard" (GB / T 14848-2017).

[0050] The above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for remediating soil contaminated by cyanide and heavy metals, characterized in that: The steps include: S1, excavating the contaminated soil to be repaired, crushing and screening the contaminated soil, removing the slag with a particle size greater than 2 cm; after screening, evenly distributing the contaminated soil on the anti-seepage layer; S2, preparing a solution of cyanide stabilizer with water, spraying it directly on the contaminated soil treated in step S1 and mixing and stirring; then performing a curing for 1 to 3 days; The cyanide stabilizer includes an activator and an oxidant; the activator includes one or more of fulvic acid, humic acid, palmitic acid and their salts; the oxidant is one or more of hydrogen peroxide and calcium peroxide; S3, fully stirring the heavy metal stabilizer and the alkaline activator to obtain a mixture, and then directly adding the mixture to the soil obtained after the primary curing in step S2 and mixing and stirring; after sufficient mixing, adjusting the soil moisture content to 20% to 30%, and performing secondary curing for 3 to 7 days; The heavy metal stabilizer is one or more of polyferric sulfate, ferric chloride, ferrous sulfate, and ferrous citrate; The alkaline activator is one or more of lime, calcium oxide, calcium sulfate, carbide slag, and neutralization slag; S4, sampling and monitoring the soil treated in step S3, detecting the leaching toxicity of heavy metals and cyanide in the soil, and comparing it with the acceptance criteria to determine whether it meets the requirements; if it does, the repaired soil that meets the standards is obtained; if it does not meet the standards, repeat the above steps S1-S3 until it meets the acceptance criteria.

2. The method for remediating cyanide-heavy metal composite contaminated soil according to claim 1, characterized in that: The mass ratio of the activator to the oxidant in the cyanide stabilizer is (0.05-0.1): (1-2).

3. The method for remediating cyanide-heavy metal composite contaminated soil according to claim 1, characterized in that: In step S3, the mass ratio of the heavy metal stabilizer to the alkaline activator in the mixture is (1-2): (0.1-0.5).

4. The method for remediating cyanide-heavy metal composite contaminated soil according to claim 1, characterized in that: In step S2, the cyanide stabilizer is added in an amount of 1% to 3% of the mass of the contaminated soil to be remediated.

5. The method for remediating cyanide-heavy metal composite contaminated soil according to claim 1, characterized in that: In step S3, the mixture is added in a ratio of 1% to 10% of the mass of the soil to be repaired.

6. The method for remediating cyanide-heavy metal composite contaminated soil according to claim 1, characterized in that: In step S2, the cyanide stabilizer is prepared into a solution with a mass percentage of 10% to 20% by water.

7. The method for remediating cyanide-heavy metal composite contaminated soil according to claim 1, characterized in that: The mass ratio of the cyanide stabilizer, the heavy metal stabilizer and the alkaline activator is (1-2):(1-2):(0.1-0.5).

8. The method for remediating cyanide-heavy metal composite contaminated soil according to claim 1, characterized in that: The pollutants in the cyanide-heavy metal composite contaminated soil are cyanide and one or more of the heavy metals As, Pb, Cu, Zn, Cd, Cr, and Mn.

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