Carbon cloth supported polypyrrole / graphene oxide / zinc oxide auxiliary electrode for soil remediation and method of making same

Abstract

The application belongs to the field of soil heavy metal remediation, and particularly relates to a carbon cloth supported polypyrrole / graphene oxide / zinc oxide auxiliary electrode for soil remediation and a preparation method thereof. A PPy / GO / ZnO ternary composite cluster 3D network structure material is prepared first; then the carbon cloth is soaked in a PPy / GO / ZnO ternary composite cluster 3D network structure material suspension, and is put into a reaction kettle to react to obtain an auxiliary electrode, which is put into a traditional electromotive remediation system to remediate various heavy metal contaminated soils by electrification. The addition of the auxiliary electrode can reduce the ion migration resistance in the soil system, improve the system current, accelerate the migration speed of heavy metal ions in the electromotive remediation system, make the electric field distribution more uniform, and produce a greater potential difference. Compared with the traditional electromotive remediation, the remediation efficiency is increased by 21% to 35%. The maximum removal rate of Pb, Cr, Cd, Cu and Ni reaches 57% to 90%.

Description

Technical Field

[0001] This invention belongs to the field of soil heavy metal remediation, specifically relating to a carbon cloth-supported polypyrrole / graphene oxide / zinc oxide auxiliary electrode for soil remediation and its preparation method. Background Technology

[0002] Globally, over 20 million hectares of land are contaminated with heavy metals such as arsenic, cadmium, copper, lead, chromium, nickel, mercury, and zinc. The main causes of heavy metal pollution are activities such as mining, smelting, fossil fuel consumption, industrial emissions, waste disposal, and agricultural irrigation. Heavy metal pollution poses a significant threat to the environment and human health, thus urgently requiring the development of effective separation technologies to remove heavy metals from soil.

[0003] In recent years, people have been committed to developing many technologies for treating heavy metal contaminated soil, such as thermal desorption, chemical leaching, phytoremediation, and microbial remediation. Cho et al. (Cho K, Kang J, Kim S, et al. Effect of organic carbonate and organic matter in thermal treatment of mercury-contaminated soil[J]. Environmental Science and Pollution Research, 2021, 28: 48184-48193) used thermal desorption technology to study the desorption behavior of mercury at different temperatures. The results showed that at 500℃ and 700℃, the desorption efficiency of mercury-contaminated soil in industrial sites was only 86.7% and 89.1%, respectively. The research findings of Guo Xiaofang were reported in the *Journal of Agricultural Environment*, Vol. 39, No. 4, 2020, pp. 1486-1493: Using heavy metal-contaminated paddy soil as the research subject, a pot experiment was conducted to study the effect of a mixed leaching agent (EDTA, GLDA, citric acid) on the chemical leaching of contaminated soil. After seven leaching cycles, the mixed leaching agent showed good removal rates of Cd, Pb, Cu, and Zn in the soil, at 44.30%, 28.78%, 26.44%, and 11.49%, respectively. In the *Chinese Journal of Food Science*, Vol. 20, No. 6, 2020, pp. 246-254, Liu Yadong identified the heavy metal Pb-tolerant and adsorbing substances through high-throughput screening. 2+ The study of yeast strains indicates that there is no direct correlation between fungal tolerance to lead ions and their adsorption capacity; low tolerance to Pb... 2+ Mitchell yeast for Pb 2+ The removal rate of lead is as high as 92.56% or more, while the removal rate of lead by the highly tolerant Rhodotorula glutinis is only 23.14%. The above traditional remediation technologies have disadvantages such as easy to cause secondary pollution, damage to the soil micro-ecological environment, and complicated operation procedures.

[0004] Electrokinetic remediation technology is favored by domestic and foreign scholars because it can in-situ repair a variety of heavy metals in a short period. Electrokinetic remediation technology mainly separates heavy metals and soil through electromigration, electroosmosis and electrophoresis. Compared with other technologies, the technology is a green remediation technology with low energy consumption and secondary pollution. SUMMARY

[0005] In view of the above and / or problems existing in the prior art, the present application is proposed. Therefore, the purpose of the present application is to overcome the deficiencies in the prior art, and to provide a main-assistant multi-electrode multi-heavy metal contaminated soil remediation method of carbon cloth supported polypyrrole / graphene oxide / zinc oxide auxiliary electrode.

[0006] To solve the above technical problems, the present application provides the following technical scheme: a main-assistant multi-electrode multi-heavy metal contaminated soil remediation method of carbon cloth supported polypyrrole / graphene oxide / zinc oxide auxiliary electrode, comprising: (1) preparing a PPy / GO / ZnO ternary composite cluster 3D network structure material; (2) soaking the carbon cloth in the PPy / GO / ZnO ternary composite cluster 3D network structure material suspension, putting it into a reaction kettle to obtain an auxiliary electrode, and putting it into a traditional electrokinetic remediation system to repair multi-heavy metal contaminated soil by power supply.

[0007] (1) preparing a PPy / GO / ZnO ternary composite cluster 3D network structure material, comprising,

[0008] (1) weighing zinc oxide (ZnO) and graphene oxide (GO) according to a weight ratio of 1:1-3:1, grinding the ZnO uniformly first, then putting the ground ZnO powder and GO powder into 150 mL of deionized water, stirring for 1 h, and ultrasonicating for 1 h to make them uniformly mixed and distributed, thereby obtaining a GO / ZnO suspension;

[0009] Preferably, the mass ratio of ZnO to GO is 2:1.

[0010] (2) weighing a volume of 1-3 mL of monomer pyrrole, and adding the monomer pyrrole into the GO / ZnO suspension to uniformly stir in an ice bath (kept below 5 DEG C) constant temperature water bath;

[0011] Preferably, the volume of the monomer pyrrole is 1 mL.

[0012] (3) adding FeCl3·6H2O with a molar ratio of 1:1-2 to 50 mL of deionized water to prepare a FeCl3 aqueous solution, slowly adding the solution to the mixed solution using a separatory funnel, and continuously stirring for 6-8 h under ice bath to make the PPy capture the GO / ZnO;

[0013] The molar ratio of monomer pyrrole to FeCl3*6H2O is 1:1.

[0014] (4) After the reaction is completed, the solution is taken out, washed with acetone three times to remove excess FeCl3*6H2O, and washed with deionized water three times to keep the material neutral; the obtained material is placed in a vacuum drying oven at 60-70 DEG C for 20-24 h to obtain PPy / GO / ZnO.

[0015] (5) The PPy / GO / ZnO is added with water to prepare a polypyrrole / graphene oxide / zinc oxide powder suspension; the concentration of the suspension is 20 g / L.

[0016] (6) After ultrasonic cleaning, the carbon cloth (50 mm*50 mm*3 mm) is subjected to acidification treatment with 10% dilute nitric acid to make it soft, and then washed with deionized water until neutral; the carbon cloth is immersed in the polypyrrole / graphene oxide / zinc oxide powder suspension, sealed in a reaction kettle and placed in a constant temperature drying machine at 120 DEG C for 6 h; the carbon cloth after compounding is placed in a vacuum drying oven at 60 DEG C for 24 h to obtain an auxiliary electrode.

[0017] The application discloses a method for repairing various heavy metal contaminated soils by using a polypyrrole / graphene oxide / zinc oxide auxiliary electrode.

[0018] The voltage gradient of the electrokinetic remediation is 1 V / cm, the electrolyte of the electrokinetic remediation is deionized water, and the remediation time is 120 h.

[0019] The auxiliary electrode is not directly electrified during the electrokinetic remediation.

[0020] The application has the following beneficial effects:

[0021] (1) The application can reduce the ion migration resistance in the soil system, improve the system current, accelerate the migration speed of heavy metal ions in the electrokinetic remediation system, make the electric field distribution more uniform, produce a larger potential difference, and has high feasibility in actual site remediation without changing the voltage gradient by introducing the auxiliary electrode.

[0022] (2) The addition of the auxiliary electrode provides a new treatment technology for treating various heavy metal contaminated soils, and compared with the traditional electrokinetic remediation, the remediation efficiency is improved by 21%-35%, and the maximum removal rate of Pb, Cr, Cd, Cu and Ni reaches 57%-90%. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1The auxiliary electrode cyclic voltammogram of the embodiment 1 of the application, wherein (a) is the cyclic voltammogram of PPy, PPy / GO and PPy / GO / ZnO at a scan rate of 10 mV / s, and (b) is the cyclic voltammogram of the auxiliary electrode of embodiment 1 at a scan rate of 5, 10, 20, 50, 100 mV / s.

[0024] Figure 2 The constant current charge-discharge curve of the auxiliary electrode of the application, wherein (a) is the constant current charge-discharge curve of embodiment 1, embodiment 2 and embodiment 3, and (b) is the constant current charge-discharge curve of the auxiliary electrode of embodiment 1 at a current density of 0.5, 1, 2, 3, 5 A / g.

[0025] Figure 3 The Nyquist curve of the auxiliary electrode of the embodiment 1 of the application.

[0026] Figure 4 The morphology and structure of PPy (a), PPy / GO / ZnO (b), carbon cloth (c) and PPy / GO / ZnO / carbon cloth (d) of the embodiment 1 of the application.

[0027] Figure 5 The device schematic diagram of the main-auxiliary multi-electrode electrokinetic remediation under different configuration conditions in the embodiment of the application, wherein the anode chamber (A), the soil chamber (S), the cathode chamber (C), the direct current power supply (P), the auxiliary electrode I and / or the auxiliary electrode II; wherein a, b, c, d are the schematic diagrams of EK1, EK2, EK3, EK4 in sequence.

[0028] Figure 6 The distribution diagram of various heavy metals in the system of the embodiment and the comparative example of the application. DETAILED DESCRIPTION

[0029] In order to make the above-mentioned purposes, features and advantages of the application more obvious and easy to understand, the specific embodiments of the application are described in detail below.

[0030] In the following description, many specific details are set forth in order to provide a thorough understanding of the application, but the application can also be practiced in other ways different from those described herein, and those skilled in the art can make similar generalizations without departing from the scope of the application, therefore the application is not limited to the specific embodiments disclosed below.

[0031] The monomer pyrrole of the application is purchased from Sinopharm Chemical Reagent Co., Ltd., and the chemical reagents used are all of analytical purity.

[0032] Embodiment 1

[0033] The preparation method of the PPy / GO / ZnO ternary composite cluster-like 3D network structure material, comprising,

[0034] (1) Take 0.2 g of ZnO and 0.1 g of GO, first grind the ZnO uniformly, then put the ground ZnO powder and GO powder into 150 mL of deionized water and stir for 1 h, and ultrasonic for 1 h to make them uniformly distributed, i.e. to obtain a GO / ZnO suspension;

[0035] (2) Take 1 mL of monomer pyrrole, add the monomer pyrrole to the GO / ZnO suspension and stir uniformly in an ice bath (kept below 5°C) constant temperature water bath;

[0036] (3) Take FeCl3·6H2O with a molar ratio of 1:1 to the monomer pyrrole and add it to 50 mL of deionized water to prepare a FeCl3 aqueous solution, slowly add it to the mixed solution using a separatory funnel, continue to stir for 6 h under ice bath, and make the PPy capture the GO / ZnO;

[0037] (4) After the reaction is completed, take it out, wash it with acetone solution three times to remove excess FeCl3·6H2O, and wash it with deionized water three times to keep the material neutral; place the obtained material in a vacuum drying oven at 60°C for 24 h, i.e. to obtain PPy / GO / ZnO.

[0038] (5) Add water to the PPy / GO / ZnO to prepare a 20 g / L polypyrrole / graphene oxide / zinc oxide powder suspension;

[0039] (6) After ultrasonic cleaning, the carbon cloth (50 mm x 50 mm x 3 mm) is acidified with 10% dilute nitric acid to make it soft, and then washed with deionized water to neutral. Soak the carbon cloth in the polypyrrole / graphene oxide / zinc oxide powder suspension, seal it in a reaction kettle and place it in a constant temperature drying machine at 120°C for 6 h. Place the composite carbon cloth in a 60°C vacuum drying oven for 24 h, i.e. to obtain an auxiliary electrode.

[0040] Example 2

[0041] The preparation method of the PPy / GO / ZnO ternary composite cluster-like 3D network structure material comprises,

[0042] (1) Take 0.1 g of ZnO and 0.1 g of GO, first grind the ZnO uniformly, then put the ground ZnO powder and GO powder into 150 mL of deionized water and stir for 1 h, and ultrasonic for 1 h to make them uniformly distributed, i.e. to obtain a GO / ZnO suspension;

[0043] (2) Take 1 mL of monomer pyrrole, add the monomer pyrrole to the GO / ZnO suspension and stir uniformly in an ice bath (kept below 5°C) constant temperature water bath;

[0044] (3) FeCl3·6H2O with a monomer pyrrole molar ratio of 1:1 was added to 50 mL of deionized water to prepare an FeCl3 aqueous solution, which was slowly added to the mixed solution using a separatory funnel, and stirring was continued for 6 h under ice bath to make PPy capture GO / ZnO;

[0045] (4) After the reaction was completed, the product was taken out, washed with acetone solution three times to remove excess FeCl3·6H2O, and washed with deionized water three times to keep the material neutral; the obtained material was placed in a vacuum drying oven at 60°C for 24 h to obtain PPy / GO / ZnO.

[0046] (5) PPy / GO / ZnO was added to water to prepare a 20 g / L polypyrrole / graphene oxide / zinc oxide powder suspension;

[0047] (6) After the carbon cloth (50 mm x 50 mm x 3 mm) was ultrasonically cleaned, it was acid-treated with 10% dilute nitric acid to make it soft, and then washed with deionized water until it was neutral. The carbon cloth was immersed in the polypyrrole / graphene oxide / zinc oxide powder suspension, sealed in a reaction kettle, and placed in a constant temperature drying machine at 120°C for 6 h. The composite carbon cloth was placed in a vacuum drying oven at 60°C for 24 h to obtain the auxiliary electrode.

[0048] Example 3

[0049] The preparation method of the PPy / GO / ZnO ternary composite cluster-like 3D network structure material comprises,

[0050] (1) 0.3 g of ZnO and 0.1 g of GO were weighed, the ZnO was first ground uniformly, and then the ground ZnO powder and GO powder were placed in 150 mL of deionized water and stirred for 1 h, and ultrasonically treated for 1 h to make them uniformly mixed and distributed, to obtain a GO / ZnO suspension;

[0051] (2) 1 mL of monomer pyrrole was weighed and added to the GO / ZnO suspension, and stirring was performed in an ice bath (kept below 5°C) constant temperature water bath to make the monomer pyrrole uniformly mixed;

[0052] (3) FeCl3·6H2O with a monomer pyrrole molar ratio of 1:1 was added to 50 mL of deionized water to prepare an FeCl3 aqueous solution, which was slowly added to the mixed solution using a separatory funnel, and stirring was continued for 6 h under ice bath to make PPy capture GO / ZnO;

[0053] (4) After the reaction was completed, the product was taken out, washed with acetone solution three times to remove excess FeCl3·6H2O, and washed with deionized water three times to keep the material neutral; the obtained material was placed in a vacuum drying oven at 60°C for 24 h to obtain PPy / GO / ZnO.

[0054] (5) The PPy / GO / ZnO was added water to prepare a 20 g / L polypyrrole / graphene oxide / zinc oxide powder suspension;

[0055] (6) The carbon cloth (50 mm x 50 mm x 3 mm) was ultrasonically cleaned and then acidized with 10% dilute nitric acid to make it soft, and then washed with deionized water until it was neutral. The carbon cloth was immersed in the polypyrrole / graphene oxide / zinc oxide powder suspension and placed in a reaction kettle, sealed and placed in a constant temperature dryer at 120°C for 6 hours. The carbon cloth after compounding was placed in a 60°C vacuum drying oven for 24 hours to obtain the auxiliary electrode.

[0056] Example 4

[0057] The PPy / GO / ZnO electrode material prepared in Example 1 was subjected to electrochemical performance testing:

[0058] In a three-electrode cell: platinum was used as the counter electrode, a saturated calomel electrode was used as the reference electrode, and PPy / GO / ZnO was used as the working electrode;

[0059] The CV test was performed at a voltage window of [-1 V, 1 V] at a scan rate of 5 mV / s, 10 mV / s, 20 mV / s, 50 mV / s and 100 mV / s;

[0060] The EIS test was performed at a frequency range of 0.1-105 Hz with an amplitude of 10 mV;

[0061] The GCD test was performed at a voltage window of [0 V, 1 V] at a current density of 0.5 A / g, 1 A / g, 2 A / g, 3 A / g and 5 A / g.

[0062] Figure 1 The CV curve of (a) shows that PPy / GO / ZnO has the largest CV curve area compared to PPy and PPy / GO, and the integral area of the CV curve is directly proportional to the amount of charge stored in the material, which indicates that PPy / GO / ZnO has good capacitive performance. In the CV test results of PPy and PPy / GO, there are no obvious redox peaks during the cathode and anode scanning, and a pair of relatively symmetrical redox peaks appears during the scanning of PPy / GO / ZnO, which is speculated to be due to the fact that PPy reduces the stacking of GO, and there are pores between the particles that allow the cations and anions of the electrolyte to diffuse easily. By doping GO and ZnO to improve the electrochemical performance of the material, the surface area is enhanced and part of the reason may be the reversible redox reaction of Zn, and due to the synergistic effect between the materials, the conductivity and specific capacitance of PPy / GO / ZnO are further improved. The CV curves of PPy / GO / ZnO material at scan rates of 5, 10, 20, 50 and 100 mV / s are as follows: Figure 1(b) shown. The PPy / GO / ZnO current peak linearly increased with the increase of scan rate, the CV curve had no obvious deformation and good symmetry and kept similar redox peaks, which indicated that the material had good ion transmission ability and reversibility, reflecting that PPy / GO / ZnO had good electrochemical stability.

[0063] Figure 2 The GCD curves show that the capacitive performance of Example 1, Example 2 and Example 3 is further analyzed under constant current charge and discharge by an electrochemical workstation, in 0.1 moL / L K3[Fe(CN)6] electrolyte solution, the potential window is [0V, 1V], and the current density is 2A / g. Figure 2 (a) The comparison of GCD curves shows that the GCD curve of Example 1 has a larger area and a longer discharge time, which further indicates that the auxiliary electrode has a higher capacitance value and better charge and discharge performance when the mass ratio of zinc oxide (ZnO) to graphene oxide (GO) is 2:1.

[0064] Figure 2 (b) As the current density increases, the discharge time and specific capacitance decrease, which indicates that the charge and discharge is a kinetic phenomenon. When the current density increases, the potential changes rapidly, and the diffusion of charges in the electrolyte between the materials needs a certain time, which cannot be timely adsorbed to the electrode surface, resulting in a decrease in specific capacitance. However, the GCD curve shape does not change significantly, and the specific capacitance changes linearly when the current density is 0.5, 1, 2, 3 and 5A / g, which further confirms the electrochemical stability.

[0065] Figure 3 The Nyquist plots of PPy, PPy / GO and PPy / GO / ZnO in (b) show linearity in the low frequency region and semicircular shape in the high frequency region. The semicircular curve in the high frequency region represents the electron transmission ability between the electrode materials, and the semicircular diameter represents the interface charge transfer resistance. The linear part in the low frequency region represents the transmission performance of ions in the electrolyte. It can be seen from the EIS diagram that the semicircular diameter of PPy / GO / ZnO electrode material is the smallest in the high frequency region, and the curve slope of the linear part is the largest compared with PPy and PPy / GO, indicating that PPy / GO / ZnO electrode material has smaller interface charge transfer resistance and lower electrolyte diffusion resistance, which shows that the composite electrode material has higher conductivity. This result is highly consistent with the results of cyclic voltammetry and charge and discharge. Through the above, it is shown that by doping GO and ZnO materials, the newly formed PPy / GO / ZnO composite electrode material has good electrochemical performance due to the synergistic effect between them, and it can be used as an auxiliary electrode for the electrokinetic remediation of soil system.

[0066] Example 5

[0067] The electrokinetic remediation experiment of the heavy metal contaminated soil includes the following steps:

[0068] (1) Soil contamination experiment: The soil sample is obtained from the sandy soil in Sichuan, dried, ground and passed through a 20 mesh sieve. The soil used is obtained from Sichuan with an average particle size of 20-40 mesh, and a mixed pollution solution of Cr, Cu, Cd, Ni and Pb is prepared by adding potassium dichromate, copper chloride, cadmium chloride, nickel chloride and lead nitrate, so that the Cr, Cu, Cd, Ni and Pb pollutants in the soil reach 1000 mg / kg, 1000 mg / kg, 1000 mg / kg, 1000 mg / kg and 1500 mg / kg respectively. After the soil is naturally dried and aged for 60 days, the soil is prepared into chromium-contaminated soil by stirring every day.

[0069] (2) Main-assistant multi-electrode electrokinetic remediation process: The heavy metal electrokinetic remediation is carried out in a remediation system made of a glass plate, as shown in Figure 5 The remediation system includes an anode chamber (A), a soil chamber (S), a cathode chamber (C) and a direct current power supply (P). The auxiliary electrode I (PPy / GO / ZnO / carbon cloth auxiliary electrode of example 1) is placed at the critical point of the anode chamber and the soil chamber, marked as EK2.

[0070] (3) The heavy metal contaminated soil is placed in the soil chamber (S) as the target remediation soil, the remediation time is set to 120 h, the voltage gradient is selected to be 1 V / cm (the length of the soil remediation chamber in the experimental device is selected to be 20 cm, i.e. the voltage is 20 V), and the electrolyte is deionized water.

[0071] The above step conditions are kept unchanged, and the traditional electrokinetic remediation is set, i.e. only the main electrode chamber is configured with a graphite plate main electrode, marked as EK1.

[0072] (4) After the electrolyte wets the soil, the power supply is turned on and the electrokinetic remediation experiment is carried out for 120 h. During the experiment, a multimeter is connected in series to measure the system current, and connected in parallel to measure the potential difference between different regions from the anode main electrode (the entire remediation device is equally divided). After the remediation experiment time is up, the power supply is turned off. At the end of the experiment, samples are taken from the five parts of the soil chamber (S1-S5) which are equally divided from the anode to the cathode). The soil samples from the five parts S1-S5 are dried, digested by hydrochloric acid-nitric acid-hydrogen acid-perchloric acid complete digestion method, and then the concentrations of Cr, Cu, Cd, Ni and Pb in the seven different regions are measured by flame atomic absorption spectrophotometry.

[0073] (5) After the remediation of the contaminated soil, the system current, the potential difference, and the maximum removal rates of heavy metals Cr, Cu, Cd, Ni and Pb of the traditional electrokinetic remediation and the main-assistant multi-electrode electrokinetic remediation are shown in Tables 1, 2 and 3.

[0074] Table 1 System current over time (mA)

[0075]

[0076] Table 2 System potential difference over time (V) for different zones (distance from main anode (cm))

[0077]

[0078] Table 3 Maximum removal of heavy metals Cr, Cu, Cd, Ni and Pb (%)

[0079] Cr Cu Cd Ni Pb EK1 76.11 60.48 71.65 45.73 46.41 EK2 77.43 65.78 79.01 56.02 52.17

[0080] Example 6

[0081] Electrokinetic remediation experiments were performed on a variety of heavy metal contaminated soils, including the following steps:

[0082] (1) Soil contamination experiment: same as Example 5.

[0083] (2) Main- auxiliary multi-electrode electrokinetic remediation process: heavy metal electrokinetic remediation was performed in a remediation system made of a glass plate, as shown in Figure 5 , which includes an anode chamber (A), a soil chamber (S), a cathode chamber (C), a direct current power supply (P), and an auxiliary electrode II (PPy / GO / ZnO / carbon cloth auxiliary electrode of Example 1) placed at the critical point of the cathode chamber and the soil chamber, denoted as EK3.

[0084] (3) The multi-metal contaminated soil was placed in the soil chamber (S) as the target remediation soil, the remediation time was set to 120 h, the voltage gradient was selected to be 1 V / cm (the length of the soil remediation chamber in the experimental device was selected to be 20 cm, i.e. the applied voltage was 20 V), and the electrolyte was selected to be deionized water.

[0085] The above step conditions were kept unchanged, and a traditional electrokinetic remediation was set up, i.e. only the main electrode chamber was configured with a graphite plate main electrode, denoted as EK1.

[0086] (4) After the electrolyte wetted the soil, the power supply was turned on and electrokinetic remediation experiments were performed for 120 h, during which a multimeter was connected in series to measure the system current and connected in parallel to measure the potential difference between different regions from the main anode (the entire remediation device was equally divided), after the remediation experiment time was up, the power supply was turned off, and at the end of the experiment, samples were taken from the five parts of the soil chamber (S1-S5, equally spaced from the anode to the cathode), the soil samples from the five parts S1-S5 were dried, digested using the hydrochloric acid-nitric acid-hydrofluoric acid-perchloric acid complete digestion method, and then the concentrations of Cr, Cu, Cd, Ni and Pb in the seven different regions were measured using a flame atomic absorption spectrophotometer.

[0087] (5) The system current, potential difference, and maximum removal rate of heavy metals Cr, Cu, Cd, Ni, and Pb in traditional electrokinetic remediation and primary-secondary multi-electrode electrokinetic remediation after the remediation of contaminated soil are shown in Tables 1, 2, and 3.

[0088] Table 1 System current change over time (mA)

[0089]

[0090] Table 2 Comparison of potential difference in different regions of the system (distance from the primary anode (cm)) (V)

[0091]

[0092] Table 3 Maximum removal rate of heavy metals Cr, Cu, Cd, Ni, and Pb (%)

[0093] Cr Cu Cd Ni Pb EK1 76.11 60.48 71.65 45.73 46.41 EK3 74.03 62.79 75.60 47.54 50.61

[0094] Example 7

[0095] The electrokinetic remediation test of the multi-heavy metal contaminated soil includes the following specific steps:

[0096] (6) Soil contamination experiment: same as Example 5.

[0097] (7) Primary-secondary multi-electrode electrokinetic remediation process: heavy metal electrokinetic remediation is carried out in a remediation system made of a glass plate, as shown in Figure 5 The remediation system includes an anode chamber (A), a soil chamber (S), a cathode chamber (C), a direct current power supply (P), an auxiliary electrode I (PPy / GO / ZnO / carbon cloth auxiliary electrode of Example 1) placed at the critical point of the anode chamber and the soil chamber, and an auxiliary electrode II (PPy / GO / ZnO / carbon cloth auxiliary electrode of Example 1) placed at the critical point of the cathode chamber and the soil chamber, denoted as EK4.

[0098] (8) The multi-heavy metal contaminated soil is placed in the soil chamber (S) as the target remediation soil, the remediation time is set to 120 h, the voltage gradient is selected to be 1 V / cm (the length of the soil remediation chamber in the experimental device is selected to be 20 cm, i.e. the voltage is 20 V), and the electrolyte is selected to be deionized water.

[0099] The above step conditions remain unchanged, and traditional electrokinetic remediation is set, i.e. only the primary electrode chamber is configured with a graphite plate primary electrode, denoted as EK1.

[0100] (9) After the electrolyte wets the soil, the power is turned on and the electrokinetic remediation experiment is carried out for 120 hours, during which the multimeter is connected in series to measure the system current and connected in parallel to measure the potential difference between different regions from the main anode electrode (the entire remediation device is equally divided), after the remediation experiment time is cut off, the power is turned off, and at the end of the experiment, sampling is carried out from the five parts (S1-S5) of the soil chamber, which are equally divided from the anode to the cathode), the soil samples of S1-S5 are dried, digested by the hydrochloric acid-nitric acid-hydrogen acid-perchloric acid complete decomposition method, and then the concentrations of Cr, Cu, Cd, Ni and Pb in seven different regions are measured by a flame atomic absorption spectrophotometer.

[0101] (10) After the contaminated soil is remediated, the system current, the potential difference, and the maximum removal rates of heavy metals Cr, Cu, Cd, Ni and Pb of the traditional electrokinetic remediation and the main-assistant multi-electrode electrokinetic remediation are shown in Tables 1, 2 and 3.

[0102] Table 1 System current change with time (mA)

[0103]

[0104] Table 2 Potential difference comparison of different regions of the system (distance from the main anode (cm))

[0105]

[0106] Table 3 Maximum removal rate of heavy metals Cr, Cu, Cd, Ni and Pb (%)

[0107] Cr Cu Cd Ni Pb EK1 76.11 60.48 71.65 45.73 46.41 EK4 84.13 73.59 81.74 64.57 57.57

[0108] The above examples show that the main-assistant multi-electrode electrokinetic remediation system adopted in the present application can achieve good results.

[0109] The present application provides a carbon cloth supported polypyrrole / graphene oxide / zinc oxide auxiliary electrode assisted main-assistant multi-electrode multi-heavy metal contaminated soil remediation method, which includes the preparation of the auxiliary electrode and the main body experiment of the electrokinetic remediation of the main-assistant multi-electrode system. A good auxiliary electrode material needs to be prepared first, which can cooperate with the main electrode to improve the electromigration ability of the system and optimize the distribution of the electric field in the electrokinetic remediation experiment, so that Cr, Cu, Cd, Ni and Pb can be removed with higher migration efficiency. The prepared auxiliary electrode is applied in the main experiment of electrokinetic remediation at the same time as the main electrode, the main electrode is connected to the power supply, and the auxiliary electrode is not directly powered on to reduce energy consumption.

[0110] The application is directed to the low efficiency of traditional electrokinetic remediation for Cr, Cu, Cd, Ni and Pb contaminated soil remediation, and the auxiliary electrode prepared to improve the electrokinetic remediation system, which is used in the research of electrokinetic remediation of Cr, Cu, Cd, Ni and Pb contaminated soil, without changing the voltage gradient, from examples 5, 6 and 7, the current of EK4 is the highest, the potential difference is the largest, and the electric field is more uniform, so that the migration speed of heavy metals is increased, thereby having a better removal rate. Without changing the electric field intensity, the addition of auxiliary electrode improves the system current, thereby improving the electrokinetic efficiency, without changing the voltage gradient, without changing the type of electric field, the addition of auxiliary electrode optimizes the electric field distribution. By preparing PPy / GO / ZnO auxiliary electrode, the current in the electrokinetic remediation system is improved, and the electric field distribution is optimized, thereby increasing the removal capacity of the auxiliary electrode for Cr, Cu, Cd, Ni and Pb.

[0111] It should be explained that the above examples are only used to illustrate the technical solutions of the application and are not limited, although the application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the application can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the application, which should be covered in the scope of the claims of the application.

Claims

1. A method for preparing a carbon cloth-supported polypyrrole / graphene oxide / zinc oxide auxiliary electrode, characterized in that, The preparation method steps are as follows: (1) Weigh zinc oxide and graphene oxide according to the weight ratio. First, grind the zinc oxide evenly, then put it and graphene oxide into deionized water and stir for 1 hour, and sonicate for 1 hour to make it evenly mixed and distributed, so as to obtain graphene oxide / zinc oxide suspension. (2) Weigh out the monomer pyrrole and add it to the graphene oxide / zinc oxide suspension. Stir it evenly in an ice bath constant temperature water bath. (3) FeCl3·6H2O was added to deionized water to prepare FeCl3 aqueous solution. The solution was then slowly added to the mixed solution in step (2) using a separatory funnel. The mixture was stirred continuously for 6-8 hours under an ice bath to allow PPy to capture GO / ZnO. (4) After the reaction is complete, remove the product and wash it three times with acetone to remove excess FeCl3·6H2O. Wash it three times with deionized water to keep the material neutral. Dry the product under vacuum to obtain polypyrrole / graphene oxide / zinc oxide. (5) Prepare a polypyrrole / graphene oxide / zinc oxide powder suspension by adding water to polypyrrole / graphene oxide / zinc oxide; (6) After ultrasonic cleaning of carbon cloth (50mm×50mm×3mm), acidify the carbon cloth with 10% dilute nitric acid to make it soft, then wash the carbon cloth with deionized water until neutral, immerse the carbon cloth in a suspension of polypyrrole / graphene oxide / zinc oxide powder, put it into a reaction vessel, seal it and place it in a constant temperature dryer at 120℃ for 6h, and then place the composite carbon cloth in a vacuum drying oven at 60℃ for 24h to obtain the auxiliary electrode.

2. The method for preparing the carbon cloth-supported polypyrrole / graphene oxide / zinc oxide auxiliary electrode as described in claim 1, characterized in that, The mass ratio of zinc oxide to graphene oxide in step (1) is 1:1 to 3:

1.

3. The method for preparing the carbon cloth-supported polypyrrole / graphene oxide / zinc oxide auxiliary electrode as described in claim 1, characterized in that, The mass ratio of the monomer pyrrole, zinc oxide and graphene oxide in step (2) is 10:2:

1.

4. The method for preparing the carbon cloth-supported polypyrrole / graphene oxide / zinc oxide auxiliary electrode as described in claim 1, characterized in that, The molar ratio of FeCl3·6H2O to pyrrole monomer in step (3) is 1:1 to 2.

5. The method for preparing the carbon cloth-supported polypyrrole / graphene oxide / zinc oxide auxiliary electrode as described in claim 1, characterized in that, Step (4) Drying temperature 60-70℃, drying time 20-24h.

6. A carbon cloth-supported polypyrrole / graphene oxide / zinc oxide auxiliary electrode prepared by the method according to any one of claims 1-5.

7. The application of the carbon cloth-supported polypyrrole / graphene oxide / zinc oxide auxiliary electrode prepared by the method according to any one of claims 1-5, characterized in that, The carbon cloth-supported polypyrrole / graphene oxide / zinc oxide serves as an auxiliary electrode material that does not directly conduct electricity. When applied to a traditional electrokinetic remediation system, it remediates soil contaminated with various heavy metals.

8. The application of the carbon cloth-supported polypyrrole / graphene oxide / zinc oxide auxiliary electrode as described in claim 7, characterized in that: Soil remediation is carried out within a remediation system, which includes an anode chamber (A), a soil chamber (S), a cathode chamber (C), a DC power supply (P), and auxiliary electrodes.

9. The application of the carbon cloth-supported polypyrrole / graphene oxide / zinc oxide auxiliary electrode as described in claim 7, characterized in that: The voltage gradient for electro-repair was 1V / cm, the electrolyte for electro-repair was deionized water, and the repair time was 120h.

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