CN113461117B - Method for treating heavy metal organic complex wastewater by electrochemical oxidation coupled with electric flocculation - Google Patents

Method for treating heavy metal organic complex wastewater by electrochemical oxidation coupled with electric flocculation Download PDF

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CN113461117B
CN113461117B CN202110772305.4A CN202110772305A CN113461117B CN 113461117 B CN113461117 B CN 113461117B CN 202110772305 A CN202110772305 A CN 202110772305A CN 113461117 B CN113461117 B CN 113461117B
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edta
electrochemical oxidation
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CN113461117A (en
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宋佩佩
杨朝晖
熊炜平
贾美莹
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Shandong Agricultural University
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Abstract

The invention discloses a method for treating Cu-EDTA heavy metal organic complex wastewater by using electrochemical oxidation coupled electrocoagulation. The heavy metal organic complexing wastewater to be treated is placed in an electrochemical oxidation-electric flocculation coupling device, current is switched on, the heavy metal organic complexing wastewater Cu-EDTA is treated, and the heavy metal organic complexing wastewater is effectively decomplexed and the Cu and COD are efficiently removed through the direct oxidation of an electrochemical anode, the indirect oxidation process and the flocculation precipitation process of electric flocculation. The invention constructs an electrochemical oxidation-electric flocculation coupling device for treating heavy metal organic complexing wastewater Cu-EDTA. The influence rule of current density, electrolyte, naCl concentration, pH and initial concentration on an EO-EC reaction system is researched. The invention couples an electrochemical oxidation method and an electric flocculation method to realize effective complex breaking of Cu-EDTA complex wastewater and efficient treatment of Cu and COD.

Description

Method for treating heavy metal organic complex wastewater by electrochemical oxidation coupled with electric flocculation
Technical Field
The invention relates to the technical field of wastewater treatment, in particular to a method for treating heavy metal organic complex wastewater by using electrochemical oxidation coupled with electric flocculation.
Background
The industries of metal ore smelting, electrolysis, electroplating and the like need to discharge a large amount of wastewater containing heavy metal ions every year, the heavy metal wastewater cannot be degraded by microorganisms when discharged into the environment, and the heavy metal wastewater can cause serious harm to human health, animals, plants and aquatic organisms through soil, water and air, especially food chains. In recent years, with the development of surface treatment technology, electroplating and chemical plating are widely applied, and the complexing agent used in the process greatly makes the components of heavy metal wastewater more complex. Taking heavy metal wastewater in the electroplating industry as an example: the electroplating wastewater contains poisonous and harmful heavy metal ions such as copper, nickel, cadmium, lead, chromium and the like, cyanide, EDTA, a surfactant, a brightener and other pollutants. Heavy metal ions usually form a complex with cyanide, EDTA or organic matters, most complex heavy metals have high water solubility and can stably exist in a wide pH range, and the complex heavy metals are difficult to remove by the existing technical processes such as chemical neutralization and precipitation. Therefore, the treatment of complex heavy metals has become one of the problems to be solved in environmental protection.
Because the interaction between heavy metal and organic matter in the complexing wastewater is influenced, a complex and stable soluble heavy metal organic complex can be formed through coordination, so that the stability of heavy metal ions is improved, the complexity and the difficult degradability of organic pollutants are improved, the effective breaking of the complexing and the efficient removal of the heavy metal are difficult to realize by the conventional technology, and the treatment of the heavy metal organic complex becomes a hot spot and a difficult point of heavy metal wastewater pollution control in recent years. The methods of treatment that are commonly used are mainly: electrochemical oxidation, electroflocculation, electro-flotation, electrodialysis, micro-electrolysis, etc. The electrochemical oxidation method is to remove pollutants in the wastewater or recover useful substances through a series of chemical reactions, electrochemical processes or physical processes in an electrochemical reactor under the action of an external electric field. The electroflocculation method utilizes the dissociation of electricity to remove pollutants in wastewater or convert toxic substances into non-toxic substances with the aid of chemical coagulants. In recent years, a technique of treating wastewater by combining these two methods has been developed. For example, patent application No. 202010774747.8 discloses a method for treating electroplating wastewater by an electrocoagulation/electrochemical oxidation coupling process, and patent application No. 201610609374.2 discloses an electrochemical comprehensive treatment process for high-concentration refractory organic wastewater, wherein the methods are respectively to perform electrocoagulation treatment and then electrochemical oxidation treatment, but not to perform synchronous coupling of two processes, and the removal rate of COD is still to be improved. Therefore, a method capable of synchronously performing electrochemical oxidation and electrocoagulation is needed, which effectively couples the two processes, simultaneously treats the heavy metal and the complex, and realizes the efficient removal of the complex in the complex wastewater and the synchronous removal and recovery of the heavy metal by optimizing reaction conditions.
Disclosure of Invention
In view of the prior art, the invention aims to provide a method for treating heavy metal organic complex wastewater by using electrochemical oxidation coupled with electric flocculation. The invention couples the electrochemical oxidation method and the electric flocculation method, and the two methods are used for processing simultaneously, thereby realizing the high-efficiency processing of Cu and COD.
In order to realize the purpose, the invention adopts the following technical scheme:
in a first aspect of the invention, a method for treating heavy metal organic complex wastewater by electrochemical oxidation coupled electroflocculation is provided, which comprises the following steps:
placing heavy metal organic complexing wastewater to be treated in an electrochemical oxidation-electric flocculation coupling device, switching on current, treating the heavy metal organic complexing wastewater, and effectively breaking the heavy metal organic complexing wastewater and efficiently removing Cu and COD through an electrochemical anode direct oxidation process, an indirect oxidation process and an electric flocculation precipitation process, preferably, before the heavy metal organic complexing wastewater is treated, adjusting the pH value of the heavy metal organic complexing wastewater to 3-9; preferably, the pH is 5 to 7.
Preferably, the heavy metal organic complex wastewater to be treated is wastewater containing Cu-EDTA.
Preferably, the electrochemical oxidation-electric flocculation coupling device comprises a reaction tank and a sampling tank, wherein the reaction tank and the sampling tank are connected through a peristaltic pump; an electro-oxidation electrode and an electro-flocculation electrode are arranged in the reaction tank, are immersed in the electrolyte and are connected in a bipolar series mode and are connected with a programmable linear direct-current power supply; the electric oxidation electrode comprises an anode plate and a second double-electrode plate, and the electric flocculation electrode comprises a first double-electrode plate and a cathode plate; the programmable linear direct current power supply is respectively connected with the anode plate and the cathode plate; the anode plate and the second bipolar plate are both DSA electrodes, and the first bipolar plate and the cathode plate are both Al electrodes.
Preferably, one end of the peristaltic pump is connected with the sampling groove through a first liquid inlet pipe and a second liquid outlet pipe respectively; the other end of the peristaltic pump is connected with the reaction tank through a second liquid inlet pipe and a first liquid outlet pipe respectively.
Preferably, a magnetic stirrer is arranged at the bottom of the sampling tank.
Preferably, the electrolyte is selected from a NaCl electrolyte solution and Na 2 SO 4 Electrolyte solution or NaNO 3 An electrolyte solution; preferably, the electrolyte is a NaCl electrolyte solution.
Preferably, the concentration of the electrolyte is 0.5 g/L-2.0 g/L; preferably, the concentration of the electrolyte is 1.0g/L.
Preferably, the current density is 2.57 to 15.43mA/cm 2 (ii) a Preferably, the current density is 10.29mA/cm 2 。
In a second aspect of the invention, the application of the method in treating heavy metal organic complex wastewater is provided.
The invention has the beneficial effects that:
(1) The invention constructs an electrochemical oxidation-Electrocoagulation (EO-EC) device for efficient treatment of heavy metal organic complexing wastewater Cu-EDTA.
(2) The invention researches the influence rule of current density, electrolyte type, naCl concentration, pH and initial concentration on an EO-EC reaction system. The removal rate and the operation cost are comprehensively considered, and the optimal reaction condition is that the current density is 10.29mA/cm 2 、C 0 (NaCl)1.0g/L、C 0 (Cu) 50mg/L, pH 7, cu and COD removal efficiency can reach 99.85% and 85.01% respectively in 60 minutes.
(3) The device is simple, the method is simple, convenient and quick, and the Cu and COD in the heavy metal organic complex wastewater can be efficiently removed.
Drawings
FIG. 1: the structure schematic diagram of the electrochemical oxidation-electric flocculation coupling device;
wherein: 1. the system comprises a reaction tank, 2, a sampling tank, 3, a peristaltic pump, 4, an anode plate, 5, a first bipolar plate, 6, a second bipolar plate, 7, a cathode plate, 8, a programmable linear direct current power supply, 9, a first liquid inlet pipe, 10, a second liquid inlet pipe, 11, a first liquid outlet pipe, 12, a second liquid outlet pipe and 13, a magnetic stirrer.
FIG. 2: SEM (a) and EDS (a) images of the reaction product;
FIG. 3: XPS spectra of Al (a) and Cu (b) in the reaction product;
FIG. 4: XRD (a) and FTIR (b) patterns of the reaction product;
FIG. 5: effect of current density on COD (a) and Cu (b) removal;
FIG. 6: the effect of electrolyte species on COD (a) and Cu (b) removal;
FIG. 7: effect of NaCl concentration on COD (a) and Cu (b) removal;
FIG. 8: effect of pH on COD (a) and Cu (b) removal;
FIG. 9: effect of initial concentration on COD (a) and Cu (b) removal.
Detailed Description
It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the disclosure. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.
Description of terms:
DSA electrode: as used in this patent, the "DSA electrode" is RuO 2 -IrO 2 a/Ti electrode.
As introduced in the background art, the interaction between heavy metals and organic matters in the complexing wastewater causes high difficulty and poor effect in separating heavy metals in a conventional mode, so that the treatment of the heavy metal organic complexing wastewater becomes a hot spot and a difficult point in heavy metal pollution control in recent years.
Based on the situation, the invention aims to provide a method for treating heavy metal organic complex wastewater by using electrochemical oxidation coupled with electroflocculation. The invention constructs an electrochemical oxidation-electric flocculation coupling device and simultaneously carries out electrochemical oxidation and electric flocculation treatment. Cu-EDTA is removed from the wastewater through the electrochemical oxidation process and the synchronous flocculation precipitation of the electric flocculation. Electrochemical oxidation is classified into direct oxidation and indirect oxidation. The direct oxidation is due to direct charge transfer and direct oxidation to M (. OH), during which Cu-EDTA is rapidly broken down and Cu 2+ And small molecule organics are released into the wastewater. Indirect oxidation relies on RuO 2 -IrO 2 HClO or ClO generated on the surface of a/Ti anode - In the course of which Cu-EDTA is oxidized homogeneously (formulae (2 to 4))Mineralization (formula (5)) to Cu 2+ 、CO 2 、NH 3 And NO 3 - . Applying current, al electrode is made of Al 3+ The form of the compound is dissolved in the solution to form various gel polymerization state Al, pollutants including Cu-EDTA, cu-EDTA oxidation intermediates and mineralization products, and the pollutants are adsorbed, collected, captured and coprecipitated with the substances and finally separated from the wastewater, so that the heavy metal can be recovered.
The bipolar series mode adopted by the invention can effectively couple the electrooxidation and the electroflocculation processes, and after the power supply is switched on, the electrooxidation decomplexing degradation reaction and the electroflocculation flocculation precipitation process can be synchronously carried out, so that the heavy metals and organic matters in the complexing wastewater can be synchronously and efficiently removed. The method can further enhance the reaction efficiency, improve the degradation efficiency of the complex and the removal rate of Cu, reduce the cost, shorten the process flow, save the occupied area and widen the application space.
Compared with the electrochemical oxidation-electric flocculation technology adopting a single electrode (concretely, see environmental science and technology, research on a citrate-nickel complex breaking mechanism of 6 months of 2018, zhao Ganlin and the like), the electrode adopts the unipolar Ti/RuO 2 -IrO 2 And a single pole iron electrode. Fe electrode producing Fe during reaction 2+ Or Fe 3+ The influence on the water chromaticity is caused, and longer filtering, standing and other processes are needed in the later period. Compared with the adoption of an iron electrode, the invention has better flocculation effect. The research on the mechanism of breaking the citric acid-nickel complex by electrooxidation-electroflocculation in the text adopts a relay to switch the electrooxidation process and the electroflocculation process, so that the two processes can not be really coupled, and compared with the method, the treatment efficiency is lower.
Compared with an electric flocculation technology which simply uses an aluminum plate as an electrode (concretely, see environmental engineering journal, tan Zhu and the like, cu-EDTA complex wastewater is treated by an aluminum-iron electrode combined electric flocculation method in 8 months of 2014), electric flocculation only has a flocculation precipitation effect, and the biggest defect is that complex or organic matters which are difficult to degrade cannot be broken and degraded, and only the complex or organic matters are flocculated into floc products, so that Cu-EDTA can be regarded as Cu-EDTA transferred from an aqueous phase solution to a solid-phase floc precipitation, and the effective degradation of the complex and the recovery of heavy metals cannot be realized. The invention is the effective coupling of the electro-oxidation and the electro-flocculation technology, complex is broken and degraded and heavy metals are removed and recovered through the flocculation, air flotation and precipitation effects of electrochemical direct oxidation, indirect oxidation and electro-flocculation, the reaction is more thorough, and the generated floc precipitation also proves that the complex is degraded into micromolecular substances. This is not possible with the single processing technique.
In order to make the technical solutions of the present application more clearly understood by those skilled in the art, the technical solutions of the present application will be described in detail below with reference to specific embodiments.
The test materials used in the examples of the present invention were all conventional in the art and commercially available.
Example 1
Electrochemical oxidation-electric flocculation coupling device
As shown in FIG. 1, the device comprises a reaction tank 1 and a sampling tank 2, wherein the reaction tank 1 and the sampling tank 2 are connected through a peristaltic pump 3; an electric oxidation electrode and an electric flocculation electrode are arranged in the reaction tank 1, are immersed in the electrolyte and are connected in series and are connected with a programmable linear direct current power supply 8; the electrooxidation electrode comprises an anode plate 4 and a second double-electrode plate 6, and the electroflocculation electrode comprises a first double-electrode plate 5 and a cathode plate 7; the programmable linear direct current power supply 8 is respectively connected with the anode plate 4 and the cathode plate 7; the anode plate 4 and the second bipolar plate 6 are both DSA electrodes, and the first bipolar plate 5 and the cathode plate 7 are both Al electrodes.
The arrangement mode of the electrode plates is as follows from left to right in sequence: an anode plate 4, a first double-electrode plate 5, a second double-electrode plate 6 and a cathode plate 7.
One end of the peristaltic pump 3 is connected with the sampling groove 3 through a first liquid inlet pipe 9 and a second liquid outlet pipe 12 respectively; the other end of the peristaltic pump is connected with the reaction tank 1 through a second liquid inlet pipe 10 and a first liquid outlet pipe 11 respectively. The bottom of the sampling groove 2 is provided with a magnetic stirrer 13.
Example 2
The method for treating the heavy metal organic complex wastewater by utilizing electrochemical oxidation coupled electrocoagulation comprises the following steps:
(1) Adjusting the pH value of the wastewater containing the Cu-EDTA to 7, wherein the initial concentration of Cu in the wastewater is 50mg/L; adding NaCl electrolyte with the concentration of 1g/L into a reaction tank of the electrochemical oxidation-electric flocculation coupling device.
(2) Placing the Cu-EDTA wastewater after pH value adjustment in a sampling tank of an electrochemical oxidation-electric flocculation coupling device, turning on a programmable linear direct current power supply and a peristaltic pump, and switching on current to enable the current density to be 10.29mA/cm 2 The peristaltic pump sends the wastewater in the sampling tank into the reaction tank through the first liquid inlet pipe and the second liquid inlet pipe; the reaction tank is used for treating the Cu-EDTA wastewater, and the removal efficiency of Cu and COD can reach 99.85 percent and 85.01 percent respectively in 60 minutes by measurement and calculation.
The morphology and elemental composition of the reaction product were explored by analysis of SEM and EDS spectra of the product, and the results are shown in fig. 2. SEM images showed the product to be a cluster amorphous structure. EDS spectral analysis shows that the product contains Al, cu, C and N, which indicates that the Cu-EDTA is removed from the waste water.
To reveal the chemical morphology of Al and Cu in the product, XPS analysis was performed on the product, as shown in fig. 3. The Al 2p peak at 74.30eV is divided into three sub-peaks at 75.06eV, 74.35eV and 74.11eV, which are respectively located at AlOOH and Al (OH) 3 And Al 2 O 3 The binding energy of (1). Due to spin-orbit splitting, two peaks which are different by 20eV appear in the Cu 2p XPS spectrum, and the oxidation state of copper can be determined according to the positions of the double peaks. Peaks appearing at 933eV and 953eV in the spectrum correspond to Cu 2p of Cu element in CuO 3/2 And Cu 2p 1/2 The binding energy of the tracks. These results indicate that the reaction product may consist of AlOOH, al (OH) 3 、Al 2 O 3 And CuO. XPS analysis confirmed that mononuclear and/or polynuclear gel polymeric aluminum was produced during the electroflocculation process.
In order to determine the product crystallinity and functional group composition, XRD and FTIR analyses were performed thereon, as shown in fig. 4 and table 1. The XRD characteristic peak is wide and shallow in distribution, which shows that the material is amorphous or has poor crystallization. In addition, naNO was also found in the product by comparison with standard PDF 3 And CuO. Research shows that after the complex of Cu-EDTA is broken, cu is obtained 2+ Released into solution, and at pH greater than 4.5, cuO or Cu 2 O is precipitated, and these CuO and Cu are precipitated 2 The O particles are finally removed from the wastewater by a flocculation process, naNO 3 Possibly the mineralization product of Cu-EDTA during electrochemical oxidation.
TABLE 1 FTIR vibrations and corresponding wavelengths
Figure BDA0003153034850000061
As can be seen from fig. 4 and table 1, FTIR analysis identified the vibration of functional groups C = O, -COOH, etc., indicating that the product contained EDTA degradation intermediates. The oxidation intermediate of Cu-EDTA may be carboxylic acid micromolecular organic matter. Cu-EDTA mineralized products (CuO and Cu) are also present in the product 2 O). The coexistence of the mineralized product of Cu-EDTA and the oxidation intermediate shows that the Cu-EDTA complex can be directly mineralized through electrochemical oxidation on one hand, and can be converted into a small molecular substance through indirect oxidation on the other hand, and then the small molecular substance is captured by gel polymerization state Al and further separated from the wastewater.
The characterization analysis of EO-EC products proves that the products contain oxidation intermediates (such as carboxylic acid) and mineralization products (such as NaNO) of Cu-EDTA 3 CuO, etc.) and flocculants (e.g., alOOH, al (OH) 3 Etc.). Electrochemical oxidation is divided into direct oxidation and indirect oxidation. The direct oxidation is due to direct charge transfer and direct oxidation to M (. OH), during which Cu-EDTA is rapidly broken down and Cu 2+ And small molecule organic matter is released into the water body. Indirect oxidation relies on RuO 2 -IrO 2 HClO or ClO generated on the surface of a/Ti anode - In the course of which Cu-EDTA is mineralized (formula (5)) and converted into Cu (formula (2-4)) 2+ 、CO 2 、NH 3 、NO 3 - Etc. (as shown in fig. 5). At the same time, al electrode is made of Al 3+ The form of the compound is dissolved in the solution to form various gel polymerization state Al oxides/hydroxides, and the various gel polymerization state Al oxides/hydroxides are adsorbed,Air flotation, rolling, net catching, coprecipitation and the like, and finally the substances are separated from the wastewater, so that the wastewater is purified.
Example 3
The current density was set to 4 levels (2.57, 5.14, 10.29, 15.43 mA/cm) as per example 2, with other conditions being unchanged 2 ). And (3) investigating the influence of different current densities on the Cu-EDTA removal efficiency.
As shown in FIG. 6, when the current density is higher than 5.14mA/cm 2 In the process, the Cu removal rate is over 99 percent and the COD removal rate is over 96 percent in 120min, and the Cu and COD removal rates and the current density have obvious positive correlation. In the electroflocculation process, higher current densities accelerate the flocculant (Al (OH) 3 AlOOH, etc.) to make the removal efficiency of Cu-EDTA faster. In the electrochemical oxidation process, the current density is increased to accelerate the direct electron transfer and the generation of OH, thereby accelerating the complex breaking process of Cu-EDTA and improving the homogeneous ClO - The efficiency of generation of (a). In addition, as the current density increases, the cathode surface H 2 Is increased in the amount of generation of large amounts of fine H 2 The bubbles are beneficial to the mixed mass transfer and air floatation processes, thereby improving the removal rate. When the current density is 15.43mA/cm 2 The removal rates of COD and Cu are higher than other current densities. The current density was set to 10.29mA/cm in consideration of power consumption and cost 2 。
Example 4
According to the method of example 2, three electrolytes of 1.0g/L were set, with other conditions being unchanged: naCl, naNO 3 、Na 2 SO 4 . And (3) investigating the influence of the electrolyte type on the Cu-EDTA removal efficiency.
As shown in FIG. 7 (a), the NaCl electrolyte solution showed higher removal rate of COD than other electrolytes, while Na 2 SO 4 With NaNO 3 Are not so different. This phenomenon may be due to different oxidation mechanisms or different oxide species in different electrolytes. The electrochemical oxidation is classified into direct oxidation and indirect oxidation, and the direct oxidation includes oxidation of M (. OH) (formula (1)) generated on the surface of the anode and direct charge transferOxidation, the main cause of the breaking of the Cu-EDTA. While ClO generated in NaCl electrolyte - Is responsible for the mineralization of Cu-EDTA. DSA anode surface Cl in NaCl electrolyte - Can be oxidized to Cl 2 (formula (2)), and further transferred to HClO (formula (3)) or ClO- (formula (4)) in an acidic or basic solution. Under the action of the homogeneous active oxychloride, the Cu-EDTA is mineralized (formula (5)), so that the treatment efficiency of NaCl serving as an electrolyte on the Cu-EDTA is higher.
M (s) +H 2 O→M(·OH)+H++e - (1)
2Cl - -2e - ＝Cl 2 (2)
Cl 2 +H 2 O＝HClO+H++Cl - (3)
HClO＝H + ClO - (4)
17ClO - +C 10 H 14 N 2 O 8 2- ＝17Cl - +10CO 2 +2NH 3 +5H 2 O (5)
NaCl was also superior as an electrolyte in terms of Cu removal rate, as shown in FIG. 7 (b), the Cu removal rate reached 95.43% and Na within 45min 2 SO 4 And NaNO 3 For Cu 2+ The removal rate of (A) is only half of that of NaCl. 1. On the one hand, as mentioned above, naCl is used as electrolyte, which can accelerate the decomplexation degradation of Cu-EDTA and generate free heavy metal Cu which can be removed more easily, on the other hand, as the reaction proceeds, the electrode surface is easy to form passivation film, and Cl - Can damage the passivation layer of the electrode and promote the dissolution of the Al anode through the pitting action, thereby accelerating the generation rate of the flocculating agent and the removal of Cu. In consideration of the advantage of NaCl on the Cu-EDTA removal rate, naCl should be used as an electrolyte to treat Cu-EDTA in the EO-EC reactor.
Example 5
According to the method of example 2, the initial NaCl concentration was set at three levels of 0.5, 1.0, 2.0 mg/L, with other conditions unchanged. And (3) investigating the influence of NaCl concentration on the Cu-EDTA removal efficiency.
Within 60min, cu at three initial NaCl concentration levels can be effectively removed, and from FIG. 8 (b), three removal rate variation trends are almost overlapped, which shows that NaCl concentration has little influence on Cu removal rate. While FIG. 8 (a) shows that the COD removal rate is positively correlated with the NaCl concentration, the removal rate of the reactor is the best among the three levels when the NaCl concentration is 2.0 g/L. In the electrochemical oxidation process with NaCl as electrolyte, cu-EDTA and its degradation intermediate can be mineralized by active oxychloride. Therefore, as the NaCl concentration increases, the amount of the active oxychloride produced increases, and the removal efficiency of COD further increases. Within 90min, the removal rate of 1.0g/L NaCl on COD reaches 90%, and the difference with the removal rate of 2.0g/L NaCl is not large. In view of cost, the NaCl concentration was set to 1.0g/L.
Example 6
The initial pH was set to four levels of 3, 5, 7 and 9, as per the method of example 2, with other conditions unchanged. And (4) investigating the influence of pH on the Cu-EDTA removal rate.
As shown in FIG. 8, within 60min, the pH was adjusted 0 7 and pH 0 The COD removal rates at 9 were 85.01% and 84.63%, respectively. However, as the initial pH decreased, the COD removal rate decreased, especially at an initial pH of 3, which was only 50.78%. Similar phenomenon also occurs in the removal rate of copper, and when the initial pH is more than 3, the removal rate of copper is not greatly affected by the pH, and when the initial pH is 3, the removal rate of copper is remarkably reduced.
Under the acidic condition, al in the solution is Al 3+ Mainly, the flocculation effect is not good, so that COD and Cu are generated 2+ The removal rate is low. At a pH of 5 to 7, the mononuclear and/or polynuclear gel polymerizes aluminum (e.g., forms Al (OH) 3 、Al(OH) 2 + 、Al 2 (OH) 4 + 、 Al 17 (OH) 32 7+ ) And generation is favorable for flocculation. Further, when the pH is higher than 9, al (OH) 3 Conversion to soluble species Al (OH) 4 - ，Al(OH) 5 2- The reduction in the type and amount of flocculant produced reduces the removal of Cu-EDTA. In the aspect of electrochemical oxidation, when the solution isWhen strongly acidic or alkaline, chlorine is mainly in the form of Cl 2 And OCl - . Research shows that HClO is larger than ClO - Has stronger oxidizing power. Thus, COD removal is higher under neutral conditions, while Cu can be effectively removed over a wider pH range.
Example 7
The initial Cu concentrations were set to 12.5, 25.0 and 50.0mg/L (m) according to the method of example 2, respectively, with other conditions unchanged Cu :m EDTA = 1:1). And (3) inspecting the influence of the initial concentration of the Cu-EDTA on the removal rate.
As shown in fig. 9, the removal rates of COD and Cu are inversely related to the initial concentrations. When C is present 0 (Cu)(m Cu :m EDTA = 1:1) at 12.5 and 25.0mg/L respectively, COD removal rates as high as 99.98% and 97.56%. When C is 0 (Cu)(m Cu :m EDTA = 1:1) was 50mg/L, the COD removal rate also reached a high value (91.01%), but was reduced relative to 12.5 or 25.0 mg/L. And copper under each concentration level is rapidly removed in the wastewater, and the removal rate has no significant difference among the three concentration levels.
It is worth noting that when C 0 (Cu)(m Cu :m EDTA = 1:1) is 50mg/L, cu in the wastewater is substantially removed within 30min, and the removal rate of COD is low. This is probably because the free Cu is obtained after the electrochemical oxidation has broken the complex of Cu-EDTA and degraded 2+ Is released into solution by flocculation by electroflocculation, cu 2+ The complex is completely removed within 45min, and at the same time, the complex breaking and degrading intermediate product may take more time to be completely removed.
Comparative example 1
(1) Adjusting the pH value of the wastewater containing the Cu-EDTA to 7, wherein the initial concentration of Cu in the wastewater is 50mg/L; naCl electrolyte with the concentration of 1.0g/L is added into the electrochemical oxidation device. The electrochemical oxidation apparatus differs from the apparatus of example 1 in that: the reaction tank is not provided with an electric flocculation electrode, and only is provided with an electric oxidation electrode. The electrooxidation electrodes are DSA electrodes and are respectively connected with a programmable linear direct current power supply.
(2) Adjusting the pH value of the Cu-EDPlacing the TA wastewater in an electrochemical oxidation device, and switching on current to make the current density be 10.29mA/cm 2 Feeding the wastewater into an electrochemical oxidation device; the electrochemical oxidation device is used for treating the Cu-EDTA wastewater, and the removal efficiency of Cu and COD is respectively 54.71 percent and 84.79 percent in 60 minutes by measurement and calculation.
Comparative example 2
(1) Adjusting the pH value of the wastewater containing the Cu-EDTA to 7, wherein the initial concentration of Cu in the wastewater is 50mg/L; a NaCl electrolyte solution having a concentration of 1.0g/L was fed into an electrochemical oxidation apparatus (the same as in comparative example 1).
(2) Placing the Cu-EDTA wastewater after the pH value is adjusted in an electrochemical oxidation device, and switching on the current to ensure that the current density is 10.29mA/cm 2 Feeding the wastewater into an electrochemical oxidation device; and treating the Cu-EDTA wastewater by using an electrochemical oxidation device to obtain first wastewater.
(3) The first wastewater was fed to an electroflocculation apparatus, which differs from the apparatus of example 1 in that: only an electric flocculation electrode and no electric oxidation electrode are arranged in the reaction tank. The electric flocculation electrodes are Al electrodes and are respectively connected with a programmable linear direct current power supply. The current was switched on so that the current density was 10.29mA/cm 2 Feeding the first wastewater into an electric flocculation device; the electric flocculation device is used for treating the first wastewater, and the Cu and COD removal efficiency is 86.93% and 88.92% respectively in 60 minutes after measurement and calculation.
Comparative example 3
(1) Adjusting the pH value of the wastewater containing the Cu-EDTA to 7, wherein the initial concentration of Cu in the wastewater is 50mg/L; naCl electrolyte at a concentration of 1.0g/L was added to an electroflocculation apparatus (the same as in comparative example 2).
(2) Placing the Cu-EDTA wastewater after the pH value is adjusted in an electric flocculation device, and switching on the current to ensure that the current density is 10.29mA/cm 2 Feeding the wastewater into an electric flocculation device; the electric flocculation device is used for treating the Cu-EDTA wastewater to obtain first wastewater.
(3) The first wastewater was fed to an electrochemical oxidation apparatus (same as comparative example 1) and the current was turned on so that the current density was 10.29mA/cm 2 Feeding the first wastewater into an electrochemical oxidation device; electrochemical oxidation apparatus pairThe wastewater is treated, and the Cu and COD removal efficiency is respectively 99.89% and 74.78% in 60 minutes by calculation.
Comparative example 4
(1) Adjusting the pH value of the wastewater containing the Cu-EDTA to 7, wherein the initial concentration of Cu in the wastewater is 50mg/L; naCl electrolyte with the concentration of 1.0g/L is added into the electrochemical oxidation-electroflocculation device. The electrochemical oxidation-electroflocculation apparatus differs from the apparatus of example 1 in that: the reaction tank is only provided with an anode plate and a cathode plate which are respectively connected with a programmable linear direct current power supply. The anode plate is a DSA electrode, and the cathode plate is an Al electrode.
(2) Placing the Cu-EDTA wastewater after the pH value is adjusted in an electrochemical oxidation-electric flocculation device, and switching on the current to ensure that the current density is 10.29mA/cm 2 Feeding the wastewater into an electrochemical oxidation-electric flocculation device; the electrochemical oxidation-electric flocculation device is used for treating the Cu-EDTA wastewater, and the Cu and COD removal efficiency is 82.69 percent and 68.45 percent respectively in 60 minutes by measurement and calculation.
The above description is only a preferred embodiment of the present application and is not intended to limit the present application, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, improvement and the like made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims (1)

1. The method for treating the heavy metal organic complex wastewater by utilizing electrochemical oxidation coupled electroflocculation is characterized by comprising the following steps of:
(1) Adjusting the pH value of the wastewater containing the Cu-EDTA to 7, wherein the initial concentration of Cu in the wastewater is 50mg/L; adding NaCl electrolyte with the concentration of 1g/L into a reaction tank of the electrochemical oxidation-electric flocculation coupling device;
(2) Placing the Cu-EDTA wastewater after pH value adjustment in a sampling tank of an electrochemical oxidation-electric flocculation coupling device, turning on a programmable linear direct current power supply and a peristaltic pump, and switching on current to enable the current density to be 10.29mA/cm 2 The peristaltic pump sends the wastewater in the sampling tank into the reaction tank through the first liquid inlet pipe and the second liquid inlet pipe; the reaction tank is used for treating the Cu-EDTA wastewater for 60min;
the electrochemical oxidation-electric flocculation coupling device comprises a reaction tank and a sampling tank, wherein the reaction tank and the sampling tank are connected through a peristaltic pump; an electric oxidation electrode and an electric flocculation electrode are arranged in the reaction tank, are immersed in the electrolyte and are connected in series and are connected with a programmable linear direct-current power supply; the electric oxidation electrode comprises an anode plate and a second double-electrode plate, and the electric flocculation electrode comprises a first double-electrode plate and a cathode plate; the programmable linear direct current power supply is respectively connected with the anode plate and the cathode plate; the anode plate and the second double-electrode plate are DSA electrodes, and the first double-electrode plate and the cathode plate are Al electrodes;
the arrangement mode of the electrode plates is as follows from left to right in sequence: the anode plate, the first double-electrode plate, the second double-electrode plate and the cathode plate;
one end of the peristaltic pump is connected with the sampling groove through a first liquid inlet pipe and a second liquid outlet pipe respectively; the other end of the peristaltic pump is connected with the reaction tank through a second liquid inlet pipe and a first liquid outlet pipe respectively; and a magnetic stirrer is arranged at the bottom of the sampling groove.
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