Method and device for recycling heavy metals in polluted soil and regenerating eluting agent

Abstract

The invention provides a method and device for recycling heavy metal in contaminated soil and regenerating an eluting agent, and relates to the technical field of washing and repairing of heavy metal contaminated soil. The method comprises the following steps: (1) in a soil leaching column, leaching the heavy metal contaminated soil by using a chelating agent solution under an ultrasonic treatment condition to form a leaching solution containing a heavy metal-chelating agent complex; (2) injecting the leacheate into an electrochemical reduction system for an electroreduction reaction to obtain regenerated leacheate; the electrochemical reduction system reacts in a double-chamber electrochemical reactor, and a cathode in the double-chamber electrochemical reactor is a PCF-MoS2 electrode; and (3) injecting the regenerated leacheate into the soil again, and leaching to form circulation. The method can improve the recovery rate of the heavy metal and the regeneration rate of the chelating agent; loss of nutrient elements in soil can be reduced by recycling the regenerated chelating agent.

Description

Technical Field

[0001] The invention belongs to the technical field of heavy metal contaminated soil washing and restoration, and specifically relates to a method and a device for realizing heavy metal recovery and eluent regeneration in contaminated soil. Background Art

[0002] Conventional strategies for remediation of heavy metal contaminated soil include soil replacement, bioremediation, and chemical fixation. However, due to limitations such as high soil replacement costs, long bioremediation time, and unstable chemical fixation, there is an urgent need to develop an efficient and low-cost heavy metal contaminated soil remediation technology.

[0003] Soil leaching technology is a time-saving and effective method for chemical remediation of heavy metals. Through leaching, heavy metals in the soil can be dissolved in the leaching solution, thereby achieving the purpose of removing heavy metals.

[0004] Chinese invention patent CN117884464A discloses a method for electrochemical enhanced leaching to repair heavy metal contaminated soil and recover heavy metals, comprising the following steps: (1) soaking the heavy metal contaminated soil, placing the electrode plate between the heavy metal contaminated soil, and arranging the anode and cathode alternately, applying an electric field in the contaminated soil to be repaired, promoting the transformation of bound heavy metals in the soil into ionic state and leaching; (2) using the Fe and Mn ions leached from the soil to generate Fe and Mn (hydroxide) composite electrodes with specific structures in situ in the electrode for 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 between the electrodes, completing the selective recovery of heavy metal ions and the regeneration of the electrode. This invention realizes the in-situ use of natural iron and manganese resources in the soil to repair heavy metal contaminated soil, and realizes the selective recovery of heavy metal ions and the regeneration of the electrode.

[0005] The key to soil leaching technology is to select a suitable leaching agent. The commonly used soil heavy metal leaching agent is the chelating agent EDTA. Studies have shown that the chelating agent EDTA can not only form stable complexes with heavy metal ions, but also control the pH of the soil within the acidic range, which is conducive to the desorption of soil heavy metals. However, the application of chelating agent leaching technology also faces some challenges: (1) The high consumption of chelating agents leads to increased costs; (2) The heavy metal complexes produced after leaching are difficult to degrade and will cause secondary pollution to the environment; (3) The leaching process is prone to excessive loss of soil nutrients.

[0006] Chinese invention patent CN116143244A provides a method for efficiently electrochemically reducing and recovering copper from wastewater containing copper complexes. The invention uses a MoS2-GF electrode as a cathode, Pt as an anode, an ion exchange membrane to separate the cathode chamber and the anode chamber, and uses wastewater containing electrolytes and the copper complex to be treated as an electrolyte to perform an electrochemical reduction reaction to obtain treated wastewater. The method uses a constant potential method to treat wastewater containing copper complexes in the cathode chamber to achieve the removal of copper complexes and the recovery of metallic copper on the electrode.

[0007] Electrochemical reduction treatment of leaching wastewater is an effective method for heavy metal recovery and chelating agent EDTA regeneration, but there is currently no technology for implementing chelating agent leaching and electrochemical reduction simultaneously, resulting in a cumbersome soil remediation process and poor economic efficiency. In view of this, it is necessary to provide a method and device for realizing the simultaneous and efficient operation of chelating agent leaching and electrochemical reduction, and utilizing the recycling of regenerated chelating agents to reduce the loss of nutrients in the soil. Summary of the invention

[0008] In view of the problems existing in the prior art, the present invention provides a method and device for recovering heavy metals in contaminated soil and regenerating eluents. The method and device utilize a chelating agent to elute heavy metal-contaminated soil under ultrasonic conditions to quickly form heavy metal complexes. The eluent is then injected into an electrochemical reduction system with a MoS2 nanosheet-loaded PAN-based carbon fiber felt (PCF-MoS2) electrode as the core to reduce and break the heavy metal complexes, thereby achieving heavy metal recovery and eluent (chelating agent) regeneration. Finally, the regenerated eluent is continuously injected into a soil elution column to circulate, thereby forming a loop as a whole.

[0009] The invention realizes the synchronous and efficient operation of the chelating agent leaching soil and the electrochemical reduction process by matching the ultrasonic power to change the heavy metal leaching rate, applying the potential to change the heavy metal recovery and chelating agent regeneration efficiency, and adjusting the process parameters such as the hydraulic retention time of the cathode chamber; the recycling of the regenerated chelating agent can reduce the Ca content in the soil. 2+ Mg 2+ , K + Loss of nutrients.

[0010] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0011] In one aspect, the present invention provides a method for recovering heavy metals from contaminated soil and regenerating an eluent, comprising the steps of:

[0012] (1) In a soil elution column, a chelating agent solution is used to elute heavy metal-contaminated soil under ultrasonic treatment conditions to form an eluent containing a heavy metal-chelating agent complex;

[0013] (2) injecting the eluent into an electrochemical reduction system for electroreduction reaction to obtain a regenerated eluent; the electrochemical reduction system reacts in a dual-chamber electrochemical reactor, and the cathode in the dual-chamber electrochemical reactor is a PCF (PAN-based carbon fiber felt)-MoS2 (molybdenum disulfide) electrode;

[0014] (3) The regenerated elution liquid is injected into the soil again for elution, thus forming a cycle.

[0015] Preferably, in step (1), the chelating agent is disodium ethylenediaminetetraacetate (EDTA-2Na).

[0016] Preferably, the initial concentration of the chelating agent solution is 0.01-0.3 mol / L.

[0017] More preferably, the initial concentration of the chelating agent solution is 0.05 mol / L.

[0018] Preferably, in the method described in the present invention, during the initial elution, a chelating agent solution needs to be added in advance to both the soil elution column and the dual-chamber electrochemical reactor; during the initial elution, the volume ratio of the chelating agent solution in the soil elution column to the volume ratio in the dual-chamber electrochemical reactor is 1-3:3.

[0019] Further preferably, initially, the volume ratio of the chelating agent solution in the soil elution column to the volume ratio in the cathode chamber is 1:3.

[0020] Preferably, in step (1), the ratio of the height to the inner diameter of the soil elution column is 10-30 cm:2-8 cm.

[0021] Preferably, in step (1), the height of the soil in the soil washing column is 50%-80% of the height of the soil washing column.

[0022] Further preferably, in step (1), the height of the soil in the soil elution column is 80% of the height of the soil elution column.

[0023] Preferably, in step (1), in the soil elution column, two filter papers are placed on both sides of the soil section as separators to prevent soil particles from entering the cathode chamber.

[0024] Preferably, in the soil elution column of step (1), the solid-liquid ratio of soil to chelating agent solution is 20-40 g:60-100 mL.

[0025] Further preferably, in the soil elution column of step (1), the solid-to-liquid ratio of soil to chelating agent solution is 30 g:80 mL.

[0026] Preferably, in step (1), the ultrasonic treatment is specifically: eluting the soil at an ultrasonic power of 100-800W.

[0027] Further preferably, the ultrasonic power is 300-400W.

[0028] Preferably, in step (2), the electrochemical reaction system is stirred magnetically to accelerate the mass transfer of pollutants.

[0029] Preferably, in step (2), the cathode is prepared by:

[0030] S1, the carbon fiber felt electrode is placed in dichloromethane, anhydrous ethanol and hydrochloric acid solution for cleaning in turn to obtain a treated carbon fiber felt electrode;

[0031] S2, ammonium molybdate tetrahydrate ((NH4)6Mo7O 24 4H2O) and thiourea (CH4N2S) are dissolved in water, and subjected to a hydrothermal reaction with the carbon fiber felt electrode treated in step S1 at 180-220° C. to obtain an electrode;

[0032] S3. Wash the electrode in step S2 multiple times and dry it to obtain a cathode.

[0033] Further preferably, in step S1, the thickness of the carbon fiber felt electrode is 1-5 mm, the porosity is 85%-95%, and the total pore area is 0.5-0.8 m 2 / g.

[0034] More preferably, in step S1, the thickness of the carbon fiber felt electrode is 2-3 mm, the porosity is 88%-94%, and the total pore area is 0.55-0.72 m 2 / g.

[0035] Further preferably, in step S1, the concentration of the hydrochloric acid solution is 0.05-0.2 mol / L.

[0036] More preferably, in step S1, the concentration of the hydrochloric acid solution is 0.1 mol / L.

[0037] Further preferably, in step S1, the cleaning time in each reagent is 0.5-1.5 h, and the cleaning is ultrasonic cleaning.

[0038] More preferably, in step S1, the ultrasonic cleaning time in each reagent is 0.5-1 h.

[0039] Further preferably, in step S2, the molar ratio of ammonium molybdate tetrahydrate to thiourea is 1:10-20.

[0040] More preferably, in step S2, the molar ratio of ammonium molybdate tetrahydrate to thiourea is 1:15.

[0041] Further preferably, in step S2, the concentration of the ammonium molybdate tetrahydrate is 0.001-0.010 mol / L.

[0042] More preferably, in step S2, the concentration of the ammonium molybdate tetrahydrate is 0.0029-0.008 mol / L.

[0043] More preferably, in step S2, the concentration of the ammonium molybdate tetrahydrate is 0.003-0.008 mol / L.

[0044] More preferably, in step S2, the concentration of the ammonium molybdate tetrahydrate is 0.0033-0.0067 mol / L.

[0045] Further preferably, in step S2, the temperature of the hydrothermal reaction is 180-220° C., and the time is 18-26 h.

[0046] More preferably, in step S2, the temperature of the hydrothermal reaction is 200-220°C and the time is 20-24h.

[0047] Further preferably, in step S3, the washing is: washing with anhydrous ethanol.

[0048] Further preferably, in step S3, the drying temperature is 50-80° C. for 2-6 hours.

[0049] Preferably, in step (2), the dual-chamber electrochemical reactor also has an anode part, and the anode is a conductive metal without catalytic properties or a conventional electrochemically stable electrode material used as an anode in electrochemistry; the present invention does not limit the anode material, and in some embodiments, the anode material is Pt.

[0050] Preferably, in step (2), the dual-chamber electrochemical reactor is connected to a power supply, and the power supply is selected from at least one of a direct current power supply and an alternating current power supply.

[0051] Preferably, in step (2), the electro-reduction reaction time is 15-60 min, that is, the residence time of the eluent in the cathode chamber is 15-60 min.

[0052] Further preferably, in step (2), the electro-reduction reaction time is 30-60 min.

[0053] On the other hand, the present invention provides a device for simultaneously realizing heavy metal recovery and eluent regeneration in heavy metal contaminated soil, comprising a dual-chamber electrochemical reactor, a power source, a soil elution column, an ultrasonic cleaning instrument, a peristaltic pump, a water inlet pipe, a water outlet pipe, and a stirrer; the dual-chamber electrochemical reactor comprises a cathode chamber, an anode chamber and a proton exchange membrane, the cathode chamber and the anode chamber are separated by the proton exchange membrane, and a cathode electrode and an anode electrode are respectively placed in the cathode chamber and the anode chamber; the positive electrode of the power source is connected to the anode electrode of the anode chamber, and the negative electrode of the power source is connected to the cathode electrode of the cathode chamber ; A stirring rod is placed in the cathode chamber and the anode chamber; the soil elution column is filled with soil, and paper is placed on both sides of the soil; the two sections of the water inlet pipe are respectively connected to the upper end of the soil elution column and the cathode chamber, and the eluent enters the cathode chamber through the water inlet pipe; the soil elution column is placed in an ultrasonic cleaning instrument, and the ultrasonic cleaning instrument contains a chelating agent solution; the lower end of the soil elution column is connected to a peristaltic pump, the peristaltic pump is connected to a water outlet pipe, and the water outlet pipe is connected to the cathode chamber; the regenerated eluent continues to be injected into the soil elution column under the action of the peristaltic pump, so as to circulate and form a loop as a whole.

[0054] Compared with the prior art, the present invention has the following beneficial effects:

[0055] (1) The present invention utilizes EDTA to elute heavy metal contaminated soil under ultrasonic conditions to quickly form an eluent containing heavy metal EDTA complexes; the eluent is then injected into an electrochemical reduction system to reduce and break the heavy metal complexes, thereby achieving heavy metal recovery and EDTA regeneration; and finally, the regenerated eluent is continuously injected into a soil elution column, thereby circulating to form a loop as a whole.

[0056] (2) In the method of the present invention, the electrochemical reaction system adopts a dual-chamber electrochemical reactor for reaction, and the cathode chamber and the anode chamber are separated by a proton exchange membrane; the electrochemical reduction system adopts PCF-MoS2 nanosheet electrodes, which can realize the reduction of metal ions in heavy metal-EDTA complexes without destroying the EDTA structure. This system can greatly improve the recovery rate of heavy metals and the regeneration rate of EDTA.

[0057] (3) When fresh EDTA is used to flush the soil using the traditional method, soil nutrient cations (Ca 2+ Mg 2+ , K + and the present invention, after the first washing cycle, the nutrient metal concentration in the EDTA solution and the nutrient metal concentration in the soil establish a balance, the method of the present invention can avoid the loss of nutrient ions in the soil by reusing the EDTA solution. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Figure 1 Schematic diagram of the device structure of Embodiment 1 to Embodiment 3 of the present invention;

[0059] Figure 2 It is a schematic diagram of the device structure of Example 4-Example 5 of the present invention.

[0060] Among them, 1. water inlet pipe; 2. paper; 3. soil elution column; 4. ultrasonic cleaner; 5. peristaltic pump; 6. water outlet pipe; 7. cathode electrode; 8. stirring bar; 9. proton exchange membrane; 10. anode electrode; 11. power supply; 12. dual-chamber electrochemical reactor; 13. cathode chamber; 14. anode chamber. DETAILED DESCRIPTION

[0061] The following non-limiting examples can enable those skilled in the art to more fully understand the present invention, but do not limit the present invention in any way. The following content is merely an exemplary description of the scope of the present invention, and those skilled in the art can make various changes and modifications to the present invention based on the disclosed content, which should also fall within the scope of the present invention.

[0062] When the embodiments give numerical ranges, it should be understood that, unless otherwise specified in the present invention, both endpoints of each numerical range and any numerical value between the two endpoints can be selected. Unless otherwise defined, all technical and scientific terms used in the present invention have the same meanings as those generally understood by those of ordinary skill in the art to which the present invention belongs.

[0063] The present invention is further described below by way of specific examples. The various chemical reagents used in the examples of the present invention are obtained through conventional commercial channels unless otherwise specified. Products from different manufacturers have no significant effect on the effects.

[0064] Example 1

[0065] The invention discloses an electrochemical method for treating a heavy metal EDTA complex eluent to achieve heavy metal recovery and EDTA regeneration.

[0066] Electrochemical reduction devices for heavy metal recovery and EDTA regeneration such as Figure 1 As shown: the positive electrode and the negative electrode of the power supply 11 are respectively connected to the anode electrode 10 and the cathode electrode 7 of the dual-chamber electrochemical reactor 12, and the stirrer 8 is used for stirring to increase the reaction mass transfer; the anode electrode 10 is placed in the anode chamber, the cathode electrode 7 is placed in the cathode chamber, and the anode chamber 14 and the cathode chamber 13 are separated by a proton exchange membrane 9; the anode electrode 10 is a platinum sheet electrode.

[0067] The electrochemical method for heavy metal recovery and EDTA regeneration is as follows: first, CuEDTA 2-The simulated wastewater was loaded into the cathode chamber of the dual-chamber electrochemical reactor. Under magnetic stirring conditions, efficient electroreduction was carried out on the surface of the PCF-MoS2 electrode (cathode). The metals were recovered on the electrode surface, and EDTA was retained for recycling, thus achieving the selective recovery of heavy metals on the electrode surface and the recovery of EDTA.

[0068] The experimental parameters are: the cathode and anode areas are 4 cm 2 , the reaction solution (simulated wastewater) is 50mL, the voltage is 5V, and the simulated wastewater contains 100mg / L CuEDTA 2- , the electrolyte concentration was 0.1M Na2SO4. After 15 min of treatment, the recovery of Cu was 99.43% and the recovery of EDTA was 99.95%.

[0069] In this embodiment, the cathode electrode is a PCF-MoS2 electrode, and its preparation method is as follows:

[0070] S1: Carbon fiber felt electrode (2 mm, porosity 90%, total pore area 0.56 m 2 / g) were placed in dichloromethane, anhydrous ethanol and 0.1 mol / L hydrochloric acid solution in sequence, and ultrasonically cleaned in each reagent for 1 h each to obtain a treated carbon fiber felt electrode for standby use;

[0071] S2: 0.1mmol (NH4)6Mo7O 24 4H2O and 1.5mmol CH4N2S were dissolved in 30mL water, and then 0.40g of the treated carbon fiber felt was transferred to a hydrothermal reactor and subjected to hydrothermal reaction at 200℃ for 20h to obtain an electrode;

[0072] S3: Wash the electrode obtained in step S2 three times with anhydrous ethanol, and dry it in a vacuum oven at 60°C for 3 h to obtain a PCF-MoS2 electrode.

[0073] Example 2

[0074] The invention discloses an electrochemical method for treating a heavy metal EDTA complex eluent to achieve heavy metal recovery and EDTA regeneration.

[0075] Electrochemical reduction devices for heavy metal recovery and EDTA regeneration such as Figure 1 As shown: the positive electrode and the negative electrode of the power supply 11 are respectively connected to the anode electrode 10 and the cathode electrode 7 of the dual-chamber electrochemical reactor 12, and the stirrer 8 is used for stirring to increase the reaction mass transfer; the anode electrode 10 is placed in the anode chamber, the cathode electrode 7 is placed in the cathode chamber, and the anode chamber 14 and the cathode chamber 13 are separated by a proton exchange membrane 9; the anode electrode 10 is a platinum sheet electrode.

[0076] The electrochemical method for heavy metal recovery and EDTA regeneration is as follows: first, PbEDTA 2- The simulated wastewater was loaded into the cathode chamber of the dual-chamber electrochemical reactor. Under magnetic stirring conditions, efficient electroreduction was carried out on the surface of the PCF-MoS2 electrode (cathode). The metals were recovered on the electrode surface, and EDTA was retained for recycling, thus achieving the selective recovery of heavy metals on the electrode surface and the recovery of EDTA.

[0077] The experimental parameters are: the cathode and anode areas are 4 cm 2 , the reaction solution (simulated wastewater) is 50mL, the voltage is 5V, and the simulated wastewater contains 100mg / L PbEDTA 2- , the electrolyte concentration was 0.1M Na2SO4. After 15 min of treatment, the recovery rate of Pb was 98.79% and the recovery rate of EDTA was 99.78%.

[0078] In this embodiment, the cathode electrode is a PCF-MoS2 electrode, and its preparation method is as follows:

[0079] S1: Carbon fiber felt electrode (3 mm, porosity 92%, total pore area 0.72 m 2 / g) were placed in dichloromethane, anhydrous ethanol and 0.1 mol / L hydrochloric acid solution in sequence, and ultrasonic cleaning was performed in each reagent for 0.5 h each to obtain a treated carbon fiber felt electrode for standby use;

[0080] S2: 0.2mmol (NH4)6Mo7O 24 4H2O and 3mmol CH4N2S were dissolved in 30mL water, and then 0.40g of the treated carbon fiber felt was transferred to a hydrothermal reactor and subjected to hydrothermal reaction at 200℃ for 24h to obtain an electrode;

[0081] S3: Wash the electrode obtained in step S2 three times with anhydrous ethanol, and then dry it in a vacuum oven at 60°C for 3 h to obtain a PCF-MoS2 electrode.

[0082] Example 3

[0083] The invention discloses an electrochemical method for treating a heavy metal EDTA complex eluent to achieve heavy metal recovery and EDTA regeneration.

[0084] Electrochemical reduction devices for heavy metal recovery and EDTA regeneration such as Figure 1 As shown: the positive electrode and the negative electrode of the power supply 11 are respectively connected to the anode electrode 10 and the cathode electrode 7 of the dual-chamber electrochemical reactor 12, and the stirrer 8 is used for stirring to increase the reaction mass transfer; the anode electrode 10 is placed in the anode chamber, the cathode electrode 7 is placed in the cathode chamber, and the anode chamber 14 and the cathode chamber 13 are separated by a proton exchange membrane 9; the anode electrode 10 is a platinum sheet electrode.

[0085] The electrochemical method for heavy metal recovery and EDTA regeneration is as follows: first, CdEDTA 2- The simulated wastewater was loaded into the cathode chamber of the dual-chamber electrochemical reactor. Under magnetic stirring conditions, efficient electroreduction was carried out on the surface of the PCF-MoS2 electrode (cathode). The metals were recovered on the electrode surface, and EDTA was retained for recycling, thus achieving the selective recovery of heavy metals on the electrode surface and the recovery of EDTA.

[0086] The experimental parameters are: the cathode and anode areas are 4 cm 2 The reaction solution (simulated wastewater) was 50 mL, the voltage was 5 V, and the simulated wastewater contained 100 mg / L CdEDTA. 2- , the electrolyte concentration was 0.1M Na2SO4. After 30min of treatment, the recovery rate of Cd was 93.62% and the recovery rate of EDTA was 99.93%.

[0087] In this embodiment, the cathode electrode is a PCF-MoS2 electrode, and its preparation method is as follows:

[0088] S1: Carbon fiber felt electrode (3 mm, porosity 88%, total pore area 0.6 m 2 / g) were placed in dichloromethane, anhydrous ethanol and 0.1 mol / L hydrochloric acid solution in sequence, and ultrasonically cleaned in each reagent for 1 h each to obtain a treated carbon fiber felt electrode for standby use;

[0089] S2: 0.2mmol (NH4)6Mo7O 24 4H2O and 3mmol CH4N2S were dissolved in 30mL water, and then 0.40g of the treated carbon fiber felt was transferred to a hydrothermal reactor and subjected to hydrothermal reaction at 200℃ for 24h to obtain an electrode;

[0090] S3: Wash the electrode obtained in step S2 three times with anhydrous ethanol, and then dry it in a vacuum oven at 60°C for 3 h to obtain a PCF-MoS2 electrode.

[0091] In Examples 1 to 3, electrolytes need to be added to the simulated wastewater during the electro-reduction reaction in order to simulate soil and enable the electro-reduction reaction to proceed normally.

[0092] Example 4

[0093] A method and device for treating heavy metal contaminated soil to achieve heavy metal recovery and regeneration of eluent EDTA.

[0094] Electrochemical reduction device for heavy metal recovery and regeneration of eluent EDTA Figure 2As shown: the positive electrode and the negative electrode of the power supply 11 are respectively connected to the anode electrode 10 and the cathode electrode 7 of the dual-chamber electrochemical reactor 12, and the stirrer 8 stirs to increase the reaction mass transfer; the anode electrode 10 is placed in the anode chamber 14, and the cathode electrode 7 is placed in the cathode chamber 13, and the anode chamber 14 and the cathode chamber 13 are separated by a proton exchange membrane 9; the anode electrode 10 is a platinum sheet electrode; the soil elution column is connected to the cathode chamber 13 through an inlet pipe 1 and an outlet pipe 6, and paper 2 is placed at each end of the contaminated soil in the soil elution column, and a loop is formed under the action of a peristaltic pump 5, and the heavy metals are accelerated to be released with the assistance of an ultrasonic cleaner 4.

[0095] The electrochemical method for heavy metal recovery and EDTA regeneration is as follows: 30 g of contaminated soil is placed in a plastic tube with a length of 10 cm and an inner diameter of 2 cm. The bulk density of the contaminated soil in the soil elution column is 0.96 g cm -3 ;The height of soil is 80% of the height of soil washing column. In the process, a total of 80mL 50mM EDTA solution, wherein the solution retained in the soil washing column is about 20mL, and the remaining solution undergoes electrochemical reduction reaction in the cathode chamber. Under the effect of peristaltic pump 5, EDTA chelating agent is pumped into the soil washing column, and the heavy metals in the soil are accelerated to be released with the assistance of ultrasonic cleaning instrument 4 (ultrasonic power is 300W), and the heavy metal-EDTA complex formed then enters the cathode chamber of the double chamber electrochemical reactor, and high-efficiency electroreduction is carried out on the surface of PCF-MoS2 electrode 7, and metal is recovered on the electrode surface, and EDTA is retained and continues to circulate and wash the soil under the effect of peristaltic pump 5, and so on repeatedly, and the restoration of contaminated soil and the recovery of heavy metals are realized. Each of the above operations is carried out synchronously.

[0096] The experimental parameters are: the cathode and anode areas are 4 cm each. 2 , the cathode chamber reaction solution is about 60mL, the voltage is 8V; the concentration of each metal in the initial contaminated soil: Cu is 2364.17mg / kg, Pb is 4082.94mg / kg, and Cd is 42.29mg / kg. After 60min of treatment, the recovery rate of Cu is 99.93%, the recovery rate of Pb is 98.89%, and the recovery rate of EDTA in the cathode chamber is 98.79%. The treated soil meets the requirements of the "Soil Environmental Quality Standard" (GB15618-2018).

[0097] In this embodiment, the cathode electrode is a PCF-MoS2 electrode, and its preparation method is as follows:

[0098] S1: Carbon fiber felt electrode (3 mm, porosity 94%, total pore area 0.58 m 2 / g) were placed in dichloromethane, anhydrous ethanol and 0.1 mol / L hydrochloric acid in sequence, and ultrasonically cleaned for 0.5 h each to obtain a treated carbon fiber felt electrode for standby use;

[0099] S2: 0.1mmol (NH4)6Mo7O 24 4H2O and 1.5mmol CH4N2S were dissolved in 30mL water, and then 0.40g of the treated carbon fiber felt was transferred to a hydrothermal reactor and subjected to hydrothermal reaction at 200℃ for 20h to obtain an electrode;

[0100] S3: Wash the electrode obtained in step S2 three times with anhydrous ethanol, and then dry it in a vacuum oven at 80°C for 2 h to obtain a PCF-MoS2 electrode.

[0101] Example 5

[0102] A method and device for treating heavy metal contaminated soil to achieve heavy metal recovery and regeneration of eluent EDTA.

[0103] Electrochemical reduction device for heavy metal recovery and regeneration of eluent EDTA Figure 2 As shown: the positive electrode and the negative electrode of the power supply 11 are respectively connected to the anode electrode 10 and the cathode electrode 7 of the dual-chamber electrochemical reactor 12, and the stirrer 8 stirs to increase the reaction mass transfer; the anode electrode 10 is placed in the anode chamber 14, and the cathode electrode 7 is placed in the cathode chamber 13, and the anode chamber 14 and the cathode chamber 13 are separated by a proton exchange membrane 9; the anode electrode 10 is a platinum sheet electrode; the soil elution column is connected to the cathode chamber 13 through an inlet pipe 1 and an outlet pipe 6, and paper 2 is placed at each end of the contaminated soil in the soil elution column, and a loop is formed under the action of a peristaltic pump 5, and the heavy metals are accelerated to be released with the assistance of an ultrasonic cleaner 4.

[0104] The electrochemical method for heavy metal recovery and EDTA regeneration is as follows: 30 g of contaminated soil is placed in a plastic tube with a length of 10 cm and an inner diameter of 2 cm. The bulk density of the contaminated soil in the soil elution column is 0.99 g cm -3 ;The height of soil is 80% of the height of soil washing column. In the process, a total of 80mL 50mM EDTA solution, wherein the solution retained in the soil washing column is about 20mL, and the remaining solution undergoes electrochemical reduction reaction in the cathode chamber. Under the effect of peristaltic pump 5, EDTA chelating agent is pumped into the soil washing column, and the heavy metals in the soil are accelerated to be released with the assistance of ultrasonic cleaning instrument 4 (ultrasonic power is 400W), and the heavy metal-EDTA complex formed then enters the cathode chamber of the double chamber electrochemical reactor, and high-efficiency electroreduction is carried out on the surface of PCF-MoS2 electrode 7, and metal is recovered on the electrode surface, and EDTA is retained and continues to circulate and wash the soil under the effect of peristaltic pump 5, and so on repeatedly, and the restoration of contaminated soil and the recovery of heavy metals are realized. The above-mentioned each operation is carried out synchronously.

[0105] The experimental parameters are: the cathode and anode areas are 4 cm each. 2, the cathode chamber reaction solution is about 60mL, and AC is used for treatment: high voltage is 10V, low voltage is -2V, AC frequency is 40Hz, and duty cycle is 80%; the concentration of each metal in the initial contaminated soil: Cu is 1963.55mg / kg, Pb is 5721.63mg / kg, and Cd is 962.28mg / kg. After 90 minutes of treatment, the recovery rate of Cu is 99.83%, the recovery rate of Pb is 98.38%, the recovery rate of Cd is 100%, and the recovery rate of EDTA in the cathode chamber is 98.53%. The treated soil meets the requirements of the "Soil Environmental Quality Standard" (GB15618-2018).

[0106] In this embodiment, the cathode electrode is a PCF-MoS2 electrode, and its preparation method is as follows:

[0107] S1: Carbon fiber felt electrode (3 mm, porosity 90%, total pore area 0.55 m 2 / g) were placed in dichloromethane, anhydrous ethanol and 0.1 mol / L hydrochloric acid in turn, and ultrasonically cleaned for 1 h each to obtain a treated carbon fiber felt electrode for standby use;

[0108] S2: 0.2mmol (NH4)6Mo7O 24 4H2O and 3mmol CH4N2S were dissolved in 70mL water, and then 0.40g of the treated carbon fiber felt was transferred to a hydrothermal reactor and subjected to hydrothermal reaction at 220℃ for 24h to obtain an electrode;

[0109] S3: Wash the electrode obtained in step S2 three times with anhydrous ethanol, and then dry it in a vacuum oven at 60°C for 4 h to obtain a PCF-MoS2 electrode.

[0110] The test results of Examples 1 to 5 show that the heavy metal recovery and eluent regeneration system constructed based on the PCF-MoS2 cathode of the present invention enables the metals in the heavy metal-EDTA complex to be efficiently and selectively reduced, while efficiently recovering the chelating agent EDTA, thereby achieving the remediation of contaminated soil.

[0111] Comparative Example 1

[0112] The difference from Example 4 is that the cathode electrode material is different. In this comparative example, the cathode electrode is a TiO2 nanotube electrode, and the preparation method is:

[0113] S1: A Ti mesh with a pore size of 150 μm was used as the substrate. The original titanium mesh was ground and polished with 240 mesh, 600 mesh and 1000 mesh sandpaper, respectively, treated in a 5wt% NaOH solution at 90°C for 60 min, corroded in a 10wt% oxalic acid solution at 90°C for 30 min, rinsed with distilled water, and placed in a 1wt% oxalic acid solution for use.

[0114] S2: High-performance reduced TiO2 is obtained by two-step anodic oxidation and one-step cathodic reduction; the first anodic oxidation is carried out in ethylene glycol electrolyte (containing 0.25wt% NH4F and 2wt% distilled water), with the pretreated Ti mesh as the anode and the Ti plate as the cathode, and oxidation is carried out at 40V for 1h to obtain TiO2; then the obtained TiO2 is directly anodized for a second time at 40V for 4h in ethylene glycol electrolyte containing 0.1wt% NH4F and 1wt% distilled water; the formed TiO2 is annealed at 450℃ in air for 2h, with a temperature rise rate of 2℃ / min; in order to further improve the performance of TiO2, at a current density of 5mA cm -2 The high-performance reduced TiO2 nanotube electrode was formed by reduction in a 10% formic acid (V:V) solution for 5 min.

[0115] The experimental parameters were the same as those in Example 4. After 60 minutes of treatment, the recovery rates of Cu, Pb, Cd, and EDTA were 25.63%, 30.42%, 17.62%, and 95.84%, respectively.

[0116] Comparative Example 2

[0117] The difference from Example 4 is that no ultrasonic treatment is performed in the soil washing column. The rest is the same as Example 4.

[0118] The experimental parameters were the same as those in Example 4. After 60 min of treatment, the recovery rates of Cu, Pb, and EDTA were 56.85%, 72.74%, and 95.46%, respectively.

[0119] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, rather than to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions of the technical solution of the present invention by ordinary technicians in this field do not deviate from the essence and scope of the technical solution of the present invention.

Claims

1. A method for recovering heavy metals from contaminated soil and regenerating eluents, characterized in that: Includes steps: (1) In a soil elution column, a chelating agent solution is used to elute heavy metal contaminated soil under ultrasonic treatment conditions to form an eluent containing a heavy metal-chelating agent complex; (2) injecting the eluent into an electrochemical reduction system for electroreduction reaction to obtain a regenerated eluent; the electrochemical reduction system reacts in a dual-chamber electrochemical reactor, and the cathode in the dual-chamber electrochemical reactor is a PAN-based carbon fiber felt-molybdenum disulfide electrode; (3) The regenerated elution liquid is injected into the soil again for elution, thus forming a cycle.

2. The method according to claim 1, characterized in that In step (1), the chelating agent is disodium ethylenediaminetetraacetate; in step (1), the initial concentration of the chelating agent solution is 0.01-0.3 mol / L.

3. The method according to claim 1, characterized in that During the initial elution, the chelating agent solution needs to be added to both the soil elution column and the dual-chamber electrochemical reactor in advance; the volume ratio of the chelating agent solution in the soil elution column to that in the dual-chamber electrochemical reactor is 1-3:

3.

4. The method according to claim 1, characterized in that: In the soil washing column of step (1), the solid-liquid ratio of soil to chelating agent solution is 20-40 g:60-100 mL; the ultrasonic treatment in step (1) is specifically: washing the soil with an ultrasonic power of 100-800 W.

5. The method according to claim 4, characterized in that The ultrasonic power of the ultrasonic treatment in step (1) is 300-400W.

6. The method according to claim 1, characterized in that In step (2), the cathode is prepared by: S1, the carbon fiber felt electrode is placed in dichloromethane, anhydrous ethanol and hydrochloric acid solution for cleaning in turn to obtain a treated carbon fiber felt electrode; S2, ammonium molybdate tetrahydrate and thiourea are dissolved in water, and subjected to a hydrothermal reaction with the carbon fiber felt electrode treated in step S1 at 180-220° C. to obtain an electrode; S3, washing the electrode in step S2, and drying to obtain a cathode.

7. The method according to claim 6, characterized in that In step S1, the thickness of the carbon fiber felt electrode is 1-5 mm, the porosity is 85%-95%, and the total pore area is 0.5-0.8 m 2 / g; In step S1, the concentration of the hydrochloric acid solution is 0.05-0.2 mol / L; in step S1, the carbon fiber felt electrode is cleaned in each reagent for 0.5-1.5 h, and the cleaning is ultrasonic cleaning.

8. The method according to claim 6, characterized in that In step S2, the molar ratio of ammonium molybdate tetrahydrate to thiourea is 1:10-20; in step S2, the concentration of ammonium molybdate tetrahydrate is 0.001-0.010 mol / L; in step S2, the temperature of the hydrothermal reaction is 180-220° C., and the time is 18-26 h; In step S3, the drying temperature is 50-80° C. for 2-6 hours.

9. The method according to claim 1, characterized in that: In step (2), the dual-chamber electrochemical reactor also has an anode, which is a conductive metal without catalytic properties or a conventional electrochemically stable electrode material used as an anode in electrochemistry; In step (2), the electroreduction reaction time is 15-60 minutes.

10. The device used in the method according to any one of claims 1 to 9, characterized in that: The invention comprises a dual-chamber electrochemical reactor (12), a power source (11), a soil washing column (3), an ultrasonic cleaning device (4), a peristaltic pump (5), a water inlet pipe (1), a water outlet pipe (6), and a stirrer (8); the dual-chamber electrochemical reactor (12) comprises a cathode chamber (13), an anode chamber (14), and a proton exchange membrane (9); the cathode chamber (13) and the anode chamber (14) are separated by the proton exchange membrane (9); a cathode electrode (7) and an anode electrode (10) are respectively placed in the cathode chamber (13) and the anode chamber (14); the positive electrode of the power source (11) is connected to the anode electrode (10) of the anode chamber (14), and the negative electrode of the power source (11) is connected to the cathode electrode (7) of the cathode chamber (13); the cathode chamber (13 ) and anode chamber (14) are placed with a stirrer (8); soil is filled in the soil elution column (3), and paper (2) is placed on both sides of the soil; two sections of the water inlet pipe (1) are respectively connected to the upper end of the soil elution column (3) and the cathode chamber (13), and the eluent enters the cathode chamber (13) through the water inlet pipe (1); the soil elution column (3) is placed in an ultrasonic cleaning instrument (4), and the ultrasonic cleaning instrument (4) contains a chelating agent solution; the lower end of the soil elution column (3) is connected to a peristaltic pump (5), and the peristaltic pump is connected to a water outlet pipe (6), and the water outlet pipe (6) is connected to the cathode chamber (13); the regenerated eluent is continuously injected into the soil elution column (3) under the action of the peristaltic pump (5), thereby circulating, and the whole constitutes a loop.

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