A method for electrochemically enhancing the elution remediation of heavy metal contaminated soil and recycling heavy metals

Abstract

This invention discloses a method for electrochemically enhanced leaching remediation of heavy metal-contaminated soil and recovery of heavy metals, comprising the following steps: 1) Wetting the heavy metal-contaminated soil and placing electrode plates between the soil layers, with the anode and cathode arranged alternately. An external electric field is applied to the soil to promote the conversion of bound heavy metals in the soil to ionic states and their leaching; 2) Fe and Mn ions leached from the soil are used to generate a Fe and Mn (hydroxide) composite electrode with a specific structure in situ within the electrode, which is used for the directional adsorption and conversion of heavy metal ions; 3) When the adsorption of heavy metal ions reaches saturation, the electrode is removed from the soil, and the adsorbed ions are gradually released by reducing or reversing the voltage of the two electrodes, thereby completing the selective recovery of heavy metal ions and the regeneration of the electrode. This invention enables in-situ remediation of heavy metal-contaminated soil using natural iron and manganese resources in the soil, and achieves selective recovery of heavy metal ions and electrode regeneration.

Description

Technical Field

[0001] This invention belongs to the field of soil remediation technology, specifically relating to a method for electrochemically enhanced leaching to remediate heavy metal-contaminated soil and recover heavy metals. Background Technology

[0002] Heavy metal pollution in soil has attracted much attention due to its high degree of concealment, long latency period, and severe consequences. Currently, a series of remediation technologies have been developed both domestically and internationally for soil pollution. Among them, soil leaching utilizes solutions containing chemical reagents to accelerate the chemical extraction process of dissolving and leaching metallic pollutants from the soil, offering advantages such as short remediation time and high efficiency. Patents CN106269842A disclose an "integrated device and method for treating Cr-contaminated soil by electrochemical oxidation and leaching" and CN117285935A discloses a "leaching agent for heavy metal-contaminated soil, an optimized leaching method, and a method of application," which can remediate heavy metal-contaminated soil. However, in practical applications, the leaching of heavy metal-contaminated soil using chelating agents also generates a large amount of water-soluble complexed heavy metal liquid. The high consumption of chelating agents, the inefficient disposal of leaching waste liquid, and the problem of soil nutrient loss limit the development of leaching technology.

[0003] To address the aforementioned issues, electrolysis technology can induce redox reactions of heavy metal compounds through electrochemical forced electron loss, using electrons as a "leaching agent" for heavy metal-contaminated soil. The external electric field enhances the reactivity of heavy metal compounds in the soil, converting them to a soluble state. Subsequently, the principle of electrochemical adsorption allows for the separation and removal of heavy metal ions from the soil. Patent CN103936116A discloses "a manganese dioxide / carbon composite electrode for electroadsorption of heavy metal ions in water and an electroadsorption method," which can achieve rapid and efficient removal of heavy metal ions from water and also enables rapid and convenient regeneration of the electrode material. However, this method has high requirements for the electrode material and is mainly used for water remediation, not for the selective recovery of heavy metals. Patent CN106269835B discloses a "soil heavy metal electro-elution leaching removal device and method based on electric geotextile". The method involves applying a leaching agent to heavy metal contaminated soil, causing positively charged heavy metals to be desorbed into the soil solution through leaching and enriched at the cathode under the action of an electric field. However, this method requires the addition of a leaching agent and the electrode material needs to be switched periodically, and cannot achieve selective recovery of heavy metals.

[0004] Therefore, this invention proposes an electrochemical enhanced leaching method for remediating heavy metal-contaminated soil and recovering heavy metals. This method can avoid secondary pollution caused by the addition of chemical reagents during the soil remediation process, and can utilize the natural iron and manganese resources of the soil in situ and realize the recovery of metal resources. Summary of the Invention

[0005] To achieve the goal of efficient remediation and recovery of heavy metals in soil contaminated with heavy metals, this invention provides a method for electrochemically enhanced leaching remediation of soil contaminated with heavy metals and recovery of heavy metals.

[0006] The technical solution adopted in this invention is as follows: A method for electrochemically enhanced leaching remediation of heavy metal-contaminated soil and recovery of heavy metals includes the following steps: 1) Wet the soil contaminated with heavy metals, place the electrode plates between the soil contaminated with heavy metals, and arrange the anode and cathode alternately, and apply an external electric field to the soil contaminated to be remediated; 2) Fe and Mn ions leached from the soil are used to generate Fe and Mn (hydrogen) oxide composite electrodes with specific structures in situ within the electrode, which are used for the directional adsorption and conversion of heavy metal ions; 3) Once the ion adsorption reaches saturation, the electrode is removed from the soil, and the adsorbed ions are gradually released by reducing or reversing the voltage between the electrodes, thus completing the selective recovery of heavy metal ions and the regeneration of the electrode.

[0007] Preferably, the anode and cathode materials in step 1) can be one of the following: carbon-based electrodes (such as activated carbon, carbon nanotubes, carbon fibers, graphene or carbon felt, etc.), noble metal alloys and their oxide materials (such as noble metals Pt, Ru, Ir, Pd, etc. and corresponding RuO2, IrO2, RhO2, etc.), or transition metal electrodes (such as Ni, Co, Mn, Zr, Nb, etc.).

[0008] Preferably, both step 1) and step 2) involve an external electric field, which is a DC electric field with a voltage of 2-20 V.

[0009] Preferably, the heavy metals in the contaminated soil are one or more of cadmium, lead, zinc, arsenic, chromium, nickel, cobalt, mercury, iron, manganese, copper, aluminum, thallium, titanium, and vanadium.

[0010] The principle of this invention: An external electric field is applied to the contaminated soil to be remediated, and the enhanced redox reaction is used to promote the conversion of inactive heavy metal compounds into soluble heavy metal ions. At the same time, the leached Fe and Mn ions are electrochemically prepared in situ to create Fe and Mn (hydrogen) oxide composite electrodes with specific structures. The electrostatic-pseudocapacitive synergy is used to further directionally adsorb and store heavy metal ions in the electrode pores, thereby achieving their separation and removal from the soil. When the heavy metal ion adsorption reaches saturation, the electrode is removed from the soil, and the adsorbed ions are gradually released by reducing or reversing the voltage of the two electrodes, thus completing the selective recovery of heavy metal ions and the regeneration of the electrode.

[0011] The present invention has the following beneficial effects: 1) This invention uses electricity to replace rinsing agents, eliminating the need for additional reagents and avoiding the problems of extra reagent input and high risk of secondary pollution associated with chemical rinsing, thus achieving green and efficient remediation.

[0012] 2) This invention enables in-situ utilization of natural iron and manganese resources in the soil to remediate soil contaminated with heavy metals, and achieves selective recovery of heavy metal ions and regeneration of electrodes. Detailed Implementation

[0013] The present invention will be further described below with reference to embodiments, but this is not intended to limit the present invention in any way. Any modifications or substitutions made based on the teachings of the present invention shall fall within the protection scope of the present invention.

[0014] Example 1 Soil samples were collected from the top 0-20cm layer of farmland surrounding a mining area and tested. The heavy metal content of the soil was shown in Table 1. The remediation area for the farmland soil samples was delineated. The specific operational steps for the electrochemical enhanced leaching remediation and recovery of heavy metals from the soil are as follows: Table 1. Soil heavy metal content (mg·kg) -1 ) heavy metal Cd Zn Ni Cu Pb As content 6.23 467.49 795.03 368.02 126.11 0.20 1) The soil contaminated with heavy metals was wetted to a moisture content of 100%, and the electrode plates were placed between the soil contaminated with heavy metals, with the anode and cathode arranged alternately. The anode material was Ru and the cathode material was carbon felt. An electric field with a voltage of 18 V was applied to the soil to be remediated to promote the conversion of bound heavy metals in the soil to ionic state and leach them out. 2) Fe and Mn ions leached from the soil are used to generate Fe and Mn (hydrogen) oxide composite electrodes with specific structures in situ within the electrode, which are used for the directional adsorption and conversion of heavy metal ions; 3) When the adsorption of heavy metal ions reaches saturation, the electrode is removed from the soil and the voltage is reduced to cause the adsorbed heavy metal ions to be gradually released, thus completing the selective recovery of heavy metal ions and the regeneration of the electrode.

[0015] After the electrochemical reaction, soil samples were tested, and the removal rate of heavy metals in the soil is shown in Table 2, with good recovery results. This indicates that the method of electrochemically enhanced leaching remediation and recovery of heavy metals in soil in this invention is effective.

[0016] Table 2. Soil heavy metal removal rate (%) element Cd Pb Zn As Cu Hg Removal rate 86.1% 84.6% 86.7% 88.3% 87.2% 92.6% Example 2 Soil samples were collected from the top 0-20cm layer of a smelter and tested. The heavy metal content of the soil was shown in Table 3. The remediation area of ​​the smelter soil samples was delineated. The specific operation steps of the electrochemical enhanced leaching remediation and recovery of heavy metals from the soil are as follows: Table 3. Soil heavy metal content (mg·kg) -1 ) heavy metal Cd Zn Ni Cu Pb As Hg content 149.01 2765.80 56.42 383.32 1371.34 200.81 2.61 1) The soil contaminated with heavy metals was wetted to a moisture content of 100%, and the electrode plates were placed between the soil contaminated with heavy metals, with the anode and cathode arranged alternately. The anode material was IrO2 and the cathode material was graphite. An external electric field with a voltage of 16 V was applied to the soil to be remediated to promote the conversion of bound heavy metals in the soil to ionic state and leach them out. 2) Fe and Mn ions leached from the soil are used to generate Fe and Mn (hydrogen) oxide composite electrodes with specific structures in situ within the electrode, which are used for the directional adsorption and conversion of heavy metal ions; 3) Once the heavy metal ion adsorption reaches saturation, the electrode is removed from the soil, and the adsorbed ions are gradually released by voltage reversal, thus completing the selective recovery of heavy metal ions and the regeneration of the electrode.

[0017] After the electrochemical reaction, soil samples were tested, and the removal rate of heavy metals in the soil is shown in Table 4, with good recovery results. This indicates that the method of electrochemically enhanced leaching remediation and recovery of heavy metals in soil in this invention is effective.

[0018] Table 4. Soil heavy metal removal rate (%) heavy metal Cd Zn Ni Cu Pb As Hg Removal rate 85.8% 84.2% 87.3% 87.9% 84.8% 85.5% 93.2% Example 3 Soil samples were collected from the top 0-20cm layer of farmland surrounding a chemical plant and tested. The heavy metal content of the soil was shown in Table 5. The remediation area for the farmland soil samples was delineated. The specific operational steps for the electrochemical enhanced leaching remediation and recovery of heavy metals from the soil are as follows: Table 5. Soil heavy metal content (mg·kg) -1 ) heavy metal Hg As Cd Co Cr Ni Pb Zn content 2.71 50.33 0.55 16.83 46.11 35.92 62.83 112.87 1) The soil contaminated with heavy metals was wetted to a moisture content of 75%, and the electrode plates were placed between the soil contaminated with heavy metals, with the anode and cathode arranged alternately. The anode was Pt and the cathode material was carbon fiber. An external electric field with a voltage of 20 V was applied to the soil to be remediated to promote the conversion of the bound heavy metals in the soil to the ionic state and leach them out. 2) Fe and Mn ions leached from the soil are used to generate Fe and Mn (hydrogen) oxide composite electrodes with specific structures in situ within the electrode, which are used for the directional adsorption and conversion of heavy metal ions; 3) Once the heavy metal ion adsorption reaches saturation, the electrode is removed from the soil, and the adsorbed ions are gradually released by voltage reversal, thus completing the selective recovery of heavy metal ions and the regeneration of the electrode.

[0019] After the electrochemical reaction, soil samples were tested, and the removal rate of heavy metals in the soil is shown in Table 6, with good recovery results. This indicates that the method of electrochemically enhanced leaching remediation and recovery of heavy metals in soil in this invention is effective.

[0020] Table 6. Soil heavy metal removal rate (%) heavy metal Hg As Cd Co Cr Ni Pb Zn Removal rate 93.7% 87.1% 91.7% 86.6% 86.9% 87.4% 85.1% 85.8% .

Claims

1. A method for electrochemically enhancing the leach remediation of heavy metal contaminated soil and the recovery of heavy metals, characterized in that, Includes the following steps: 1) The soil contaminated with heavy metals is wetted, and electrode plates are placed between the soil layers, with anodes and cathodes arranged alternately. An external electric field is applied to the soil to be remediated to promote the conversion of bound heavy metals in the soil to ionic states and their leaching. The anode and cathode materials are one of carbon-based electrodes, noble metal alloys and their oxides, or transition metal electrodes. The noble metal alloys and their oxides are any one or more of the noble metals Pt, Ru, Ir, Pd, and their corresponding RuO2, IrO2, and RhO2. The carbon-based electrodes are any one or more of activated carbon, carbon nanotubes, carbon fibers, graphene, and carbon felt. The heavy metals in the contaminated soil are one or more of cadmium, lead, zinc, arsenic, chromium, nickel, cobalt, mercury, iron, manganese, copper, aluminum, thallium, titanium, and vanadium. 2) Fe and Mn ions leached from the soil are used to generate Fe and Mn oxide composite electrodes and / or hydroxide composite electrodes in situ within the electrodes. The electrostatic-pseudocapacitive synergistic effect is used to further directionally adsorb and store heavy metal ions in the electrode pores for the directional adsorption and conversion of heavy metal ions. 3) Once the heavy metal ion adsorption reaches saturation, the electrode is removed from the soil. The adsorbed ions are gradually released by reducing or reversing the voltage between the electrodes, thus completing the selective recovery of heavy metal ions and the regeneration of the electrode.

2. The method of claim 1, wherein, The transition metal electrode is any one or more of Ni, Co, Mn, Zr, and Nb electrodes.

3. The method of claim 1, wherein, The applied electric field is a DC electric field with a voltage of 2-20V.