A process for efficiently recycling copper and EDTA ligand in Cu-EDTA-containing wastewater

Abstract

The application discloses a kind of high-efficiency resource recycling process for copper and EDTA ligand in Cu-EDTA-containing wastewater, which first adjusts the pH of Cu-EDTA-containing wastewater to be greater than or equal to 11.0, then adds an appropriate amount of formaldehyde and copper powder to the wastewater, the copper powder catalyzes the formaldehyde to generate hydrogen radicals, the hydrogen radicals reduce Cu in the metal complex to elemental copper, realizing the decomplexation of Cu-EDTA, then the zero-valent copper in the wastewater is recovered by the way of standing precipitation. 2+ In addition, the above-mentioned reduction and decomplexation reaction can also avoid the decomposition of EDTA, and the EDTA ligand in the solution can be recovered by adjusting the pH of the supernatant to be 3.0, the recovery of EDTA can reduce the concentration of total nitrogen (TN) in the wastewater, thereby significantly reducing the total nitrogen load of subsequent biochemical reaction, which is beneficial to realize the discharge requirement of effluent TN. This process realizes the simultaneous recovery of copper and EDTA ligand from electroplating wastewater for the first time, which has the advantages of economic efficiency, simple operation, easy engineering application, etc.

Description

Technical Field

[0001] This invention relates to the field of heavy metal industrial wastewater treatment technology, and in particular to a process for the efficient resource recovery of copper and EDTA ligands from Cu-EDTA-containing wastewater. Background Technology

[0002] In electroplating, printed circuit boards, and other industries, EDTA is used extensively as a ligand to complex Cu. 2+ Forming a stable octahedral structure to prevent Cu 2+ Precipitation occurs. Therefore, wastewater from electroplating, printed circuit board manufacturing, and related industries contains large amounts of Cu(II)-EDTA. Cu(II)-EDTA can exist stably in wastewater and exhibits strong biotoxicity, making it difficult for traditional biochemical treatment processes to effectively remove. Therefore, we urgently need to find a green and economical water treatment process to efficiently remove Cu(II)-EDTA from wastewater containing Cu(II)-EDTA. 2+ .

[0003] Currently, advanced oxidation technology coupled with alkaline precipitation is the most important process for treating wastewater containing Cu(II)-EDTA. The reaction mechanism is as follows: hydroxyl radicals (·OH) generated by advanced oxidation technology break down the Cu-EDTA complex, releasing Cu. 2+ Then, lime or sodium hydroxide is added to adjust the wastewater to alkalinity, releasing free Cu. 2+ With OH - The reaction produces Cu(OH)₂ precipitate, and this method is effective in removing heavy metals and organic matter from wastewater. However, the advanced oxidation coupled with alkaline precipitation method for treating electroplating wastewater has the following drawbacks: First, the advanced oxidation coupled with alkaline precipitation method has a long process flow, is difficult to operate and manage, requires large investment, consumes a large amount of reagents (hydrogen peroxide), and has high operating costs; Second, in the process of treating Cu(II)-EDTA wastewater, the advanced oxidation coupled with alkaline precipitation method generally requires the use of lime or sodium hydroxide to adjust the pH value of the wastewater, which will generate a large amount of copper-containing sludge, which is a hazardous waste and can easily cause secondary pollution if not disposed of properly; Third, the complex breaking rate of the advanced oxidation method is slow, and it usually takes several weeks to completely decompose the metal complexes in the Cu(II)-EDTA wastewater and release metal ions; Fourth, after treatment by the advanced oxidation coupled with alkaline precipitation method, the effluent quality of Cu(II)-EDTA wastewater is not very stable, and the concentration of copper heavy metal ions in the effluent sometimes exceeds the limit of the discharge standard, requiring the addition of membrane separation technology, which increases the wastewater treatment cost. Clearly, existing treatment technologies are no longer able to meet increasingly stringent emission standards. Furthermore, current advanced oxidation technologies coupled with alkaline precipitation methods struggle to recover metallic copper from complexed wastewater, resulting in resource waste and contradicting the current emphasis on green and sustainable development.

[0004] To address the problems of high treatment cost, poor timeliness, unstable effluent quality, easy secondary pollution, and inability to recover metallic copper from wastewater in existing advanced oxidation-coupled alkaline precipitation methods for treating Cu(II)-EDTA-containing wastewater, this invention provides a Cu... 0 / HCHO advanced reduction technology can achieve efficient complex breaking of Cu(II)-EDTA in wastewater and efficient recovery of metallic copper. Summary of the Invention

[0005] The purpose of this invention is to solve the technical problems existing in the prior art and to provide a method for resource-based treatment of complexed wastewater containing Cu-EDTA.

[0006] To achieve the above objectives, the technical solution provided by the present invention is as follows:

[0007] Firstly, a process for efficient resource recovery of copper from Cu-EDTA-containing wastewater is provided, which specifically includes the following steps:

[0008] Step 1: Add an appropriate amount of formaldehyde to the Cu-EDTA-containing wastewater to obtain a mixed system;

[0009] Step 2: Adjust the pH of the mixture to the specified range;

[0010] Step 3: Add an appropriate amount of copper powder to the mixture to catalyze the formation of hydrogen free radicals from formaldehyde;

[0011] Step 4: Hydrogen radicals reduce and break the complex of Cu(II)-EDTA in the mixed system to generate elemental copper. After the reaction is completed, the mixture is allowed to stand and precipitate to achieve solid-liquid separation and recover elemental copper.

[0012] Preferably, the formaldehyde added in step 1 is commercial-grade formaldehyde, and the molar ratio of formaldehyde added to Cu(II) is 1:1 to 1:50.

[0013] Preferably, the specified range in step 2 is: pH ≥ 11.0.

[0014] Preferably, the amount of copper powder added in step 3 is 0.1 to 2.0 g / L, and the added copper powder is preferably commercial grade copper powder.

[0015] Secondly, a process for efficient resource recovery of EDTA ligands from Cu-EDTA-containing wastewater is provided, which specifically includes the following steps:

[0016] Step 1: Add an appropriate amount of formaldehyde to the Cu-EDTA-containing wastewater to obtain a mixed system;

[0017] Step 2: Adjust the pH of the mixture to the specified range;

[0018] Step 3: Add an appropriate amount of copper powder to the mixture to catalyze the formation of hydrogen free radicals from formaldehyde;

[0019] Step 4: Hydrogen radicals reduce and break the complex of Cu(II)-EDTA in the mixed system to generate elemental copper. After the reaction is complete, the mixture is allowed to stand and precipitate to achieve solid-liquid separation and recover elemental copper.

[0020] Step 5: Adjust the pH of the supernatant to the specified range. After standing for 2 hours, a large amount of white precipitate appeared at the bottom of the solution. After filtration and recovery, it was characterized by infrared spectroscopy and confirmed to be a high-purity EDTA salt.

[0021] Preferably, the formaldehyde added in step 1 is commercial-grade formaldehyde, and the molar ratio of formaldehyde added to Cu(II) is 1:1 to 1:50.

[0022] Preferably, the specified range in step 2 is: pH ≥ 11.0.

[0023] Preferably, the amount of copper powder added in step 3 is 0.1 to 2.0 g / L, and the added copper powder is preferably commercial grade copper powder.

[0024] Preferably, the specified range in step 5 is: pH ≤ 3.0.

[0025] Beneficial effects of this invention:

[0026] 1. This invention enables the recovery of metals and ligands from Cu-EDTA-containing wastewater, achieving the reduction and resource utilization of target pollutants at the source, and creating favorable conditions for subsequent wastewater treatment and its compliance with discharge standards.

[0027] 2. This invention is simple to operate, does not require complex equipment during processing, has low operating costs, and is easy to implement in engineering applications. Attached Figure Description

[0028] The accompanying drawings, which are provided to further illustrate the invention and constitute a part of this invention, are illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention.

[0029] Figure 1 At an initial pH of 13.0, Cu(II)-EDTA in Cu 0 Comparison of Cu(II) removal effects in HCHO and CuO / HCHO systems;

[0030] Figure 2 At an initial pH of 13.0, Cu 0 Electron paramagnetic resonance spectrum of the / HCHO system;

[0031] Figure 3Wastewater containing Cu(II)-EDTA was treated with Cu 0 After treatment with the HCHO system, a reaction precipitate Cu was obtained. 0 X-ray crystal diffraction pattern;

[0032] Figure 4 Infrared image of EDTA obtained by acidification and recovery of the supernatant;

[0033] Figure 5 : Cu(II)-EDTA in Cu under different initial pH conditions 0 Graph showing the Cu(II) removal effect in the HCHO system;

[0034] Figure 6 At an initial pH of 13.0, Cu(II)-EDTA reacted with different Cu... 0 Cu dosage 0 Graph showing the Cu(II) removal effect in the HCHO system;

[0035] Figure 7 At an initial pH of 13.0, Cu 0 Under the condition of Cu(II)-EDTA at different concentrations of HCHO, Cu(II)-EDTA was used to treat Cu(II)-EDTA at a concentration of 1.0 g / L. 0 Graph showing the Cu(II) removal effect in the HCHO system;

[0036] Figure 8 At an initial pH of 13.0, Cu 0 The initial dosage was 1.0 g / L, and the feed ratio of HCHO to Cu(II) was 30. Different initial concentrations of Cu(II)-EDTA were used in Cu... 0 Graph showing the Cu(II) removal effect in the HCHO system;

[0037] Figure 9 At an initial pH of 13.0, Cu 0 The initial concentrations of HCHO and Cu(II)-EDTA were 1.0 g / L, 8 mM, and 240 mM, respectively. Common anions and cations in wastewater affect Cu... 0 The effect of Cu(II) removal efficiency in the / HCHO system. Detailed Implementation

[0038] This section will describe in detail specific embodiments of the present invention. Preferred embodiments of the present invention are shown in the accompanying drawings. The purpose of the drawings is to supplement the textual description with graphics, so that people can intuitively and vividly understand each technical feature and overall technical solution of the present invention, but they should not be construed as limiting the scope of protection of the present invention.

[0039] A preferred embodiment of the present invention provides a process for efficient resource recovery of copper from Cu-EDTA-containing wastewater, the process specifically comprising the following steps:

[0040] Step 1: Add an appropriate amount of formaldehyde to the Cu-EDTA-containing wastewater to obtain a mixed system;

[0041] Step 2: Adjust the pH of the mixture to the specified range;

[0042] Step 3: Add an appropriate amount of copper powder to the mixture to catalyze the formation of hydrogen free radicals from formaldehyde;

[0043] Step 4: Hydrogen radicals reduce and break the complex of Cu(II)-EDTA in the mixed system to generate elemental copper. After the reaction is completed, the mixture is allowed to stand and precipitate to achieve solid-liquid separation and recover elemental copper.

[0044] In this embodiment, the formaldehyde added in step 1 is commercial-grade formaldehyde, and the molar ratio of formaldehyde added to Cu(II) is 1:1 to 1:50.

[0045] In this embodiment, the specified range in step 2 is: pH ≥ 11.0.

[0046] In this embodiment, the amount of copper powder added in step 3 is 0.1 to 2.0 g / L, and the added copper powder is preferably commercial grade copper powder.

[0047] It should be noted that in this embodiment, during the oxidation and complex-breaking process of the metal complex, EDTA decomposes into a large amount of nitrogen-containing "secondary pollutants," resulting in a high total nitrogen content in the wastewater. Even after subsequent environmental treatment, the total nitrogen concentration in the wastewater remains high. Furthermore, increasingly stringent wastewater total nitrogen discharge standards are placing new environmental pressures on relevant enterprises. In view of this, another preferred embodiment of the present invention provides a process for the efficient resource recovery of EDTA ligands from Cu-EDTA-containing wastewater. This process specifically includes the following steps:

[0048] Step 1: Add an appropriate amount of formaldehyde to the Cu-EDTA-containing wastewater to obtain a mixed system;

[0049] Step 2: Adjust the pH of the mixture to the specified range;

[0050] Step 3: Add an appropriate amount of copper powder to the mixture to catalyze the formation of hydrogen free radicals from formaldehyde;

[0051] Step 4: Hydrogen radicals reduce and break the complex of Cu(II)-EDTA in the mixed system to generate elemental copper. After the reaction is complete, the mixture is allowed to stand and precipitate to achieve solid-liquid separation and recover elemental copper.

[0052] Step 5: Adjust the pH of the supernatant to the specified range. After standing for 2 hours, a large amount of white precipitate appeared at the bottom of the solution. After filtration and recovery, it was characterized by infrared spectroscopy and confirmed to be a high-purity EDTA salt.

[0053] In this embodiment, the formaldehyde added in step 1 is commercial-grade formaldehyde, and the molar ratio of formaldehyde added to Cu(II) is 1:1 to 1:50.

[0054] In this embodiment, the specified range in step 2 is: pH ≥ 11.0.

[0055] In this embodiment, the amount of copper powder added in step 3 is 0.1 to 2.0 g / L, and the added copper powder is preferably commercial grade copper powder.

[0056] In this embodiment, the specified range in step 5 is: pH ≤ 3.0.

[0057] Technical principle of the invention:

[0058] (1)Cu 2+ During the formation of a coordination complex with EDTA, its empty orbitals undergo sp3d2 hybridization, forming a longitudinally elongated octahedral structure (i.e., the Jahn-Teller effect), thus forming a stable six-coordinate complex with EDTA. Formaldehyde is an inexpensive industrial raw material. We found that under alkaline conditions, copper powder can catalyze the formation of formic acid and hydrogen radicals from formaldehyde (Tishchenko reaction). Hydrogen radicals are highly reactive species with a reduction potential as high as -2.1V (vs RHE), capable of breaking down the Cu in the coordination complex. 2+ Reduced to Cu 0 The empty orbitals involved in sp3d2 hybridization will be occupied by electrons, disrupting their coordination complex structure. Copper precipitation and separation can then be achieved through a simple static precipitation method. Therefore, Cu 0 / HCHO advanced reduction technology can achieve efficient complex breaking of Cu-EDTA in wastewater and efficient recovery of heavy metal copper.

[0059] (2) Compared with advanced oxidation complex-breaking technology, advanced reduction complex-breaking technology has a higher complex-breaking efficiency and can also avoid the degradation of EDTA. The solubility of EDTA in water is related to its form. Under alkaline conditions, EDTA mainly exists in the ionic state Y. 4-It exists in the supernatant with high solubility (11.1 g / L); however, in acidic solutions (pH ≤ 3), it exists as H4Y with low solubility (0.1 g / L). Therefore, EDTA in the supernatant can be recovered by adjusting the pH of the system. Experimental results show that after adjusting the pH of the supernatant to 3.0 and allowing it to stand for 2 hours, a large amount of white precipitate appears at the bottom of the solution. After filtration and recovery, the precipitate is characterized by infrared spectroscopy, confirming it to be high-purity EDTA salt. In addition, the recovery of EDTA can reduce the concentration of total nitrogen (TN) in the wastewater, thereby significantly reducing the total nitrogen load of subsequent biochemical reactions and helping to meet the TN discharge requirements of the effluent.

[0060] This invention enables the recovery of metals and ligands from Cu-EDTA-containing wastewater, achieving both volume reduction and resource recovery of the target pollutants at the source, thus creating favorable conditions for subsequent wastewater treatment and achieving discharge standards. This invention is simple to operate, requires no complex equipment, has low operating costs, and is easily applicable in engineering projects.

[0061] Implementation Case 1

[0062] Referring to the parameters of actual Cu(II)-EDTA complexed wastewater, a simulated reaction solution with an initial Cu(II)-EDTA concentration of 8 mM was prepared. At room temperature (25±3℃), 50 mL of the 8 mM Cu(II)-EDTA solution was transferred to a 100 mL volumetric flask using a graduated cylinder, and the flask was placed in a shaking incubator. HCHO solution was added to the reactor at a concentration 10 times the Cu(II)-EDTA (molar stoichiometry), and the HCHO was allowed to disperse evenly in the solution. The initial pH of the reaction solution was adjusted to a specified value (pH = 13.0) using NaOH solution (10 mol / L) and H2SO4 solution (10 mol / L), and then copper powder was added. 0 The initial concentration was 1.0 g / L. After the reaction started, 1 mL of reaction sample was transferred from the reaction system at specified reaction time points (0, 1, 3, 5, 7, and 9 h). The concentration of Cu(II) in the supernatant was analyzed after filtering the reaction solution through a 45 μm pore size filter membrane. All experiments were repeated at least three times, and the average value and standard error of the experimental data were calculated.

[0063] Experimental results are as follows Figure 1 As shown, at an initial pH of 13.0, Cu(II)-EDTA in Cu alone 0 There was no significant removal effect in the HCHO system. And Cu... 0 The / HCHO system effectively removed Cu(II) from the solution. After 10 hours of reaction, the concentration of copper ions in the solution was below the instrument's detection limit (<0.05 mg / L). Subsequently, Cu was analyzed using electron paramagnetic resonance (EPR). 0Active species in the / HCHO system. For example... Figure 2 As shown, after 10 minutes of reaction, in Cu 0 A ninefold signal peak belonging to the DMPO-H adduct was detected in the / HCHO system, preliminarily confirming Cu 0 In the / HCHO system, H· is the main active species for reducing Cu(II)-EDTA. After the reduction reaction of Cu(II)-EDTA is complete, a red precipitate is obtained by static precipitation. For example... Figure 3 As shown, after freeze-drying, X-ray diffraction (XRD) analysis revealed that the composition was high-purity zero-valent copper, and the recovery rate of copper ions in the wastewater was close to 100%.

[0064] Compared with advanced oxidative complexation technology, advanced reductive complexation technology has a higher complexation efficiency and can also avoid EDTA degradation. Subsequently, by adjusting the pH of the supernatant to ≤3.0 and allowing the reaction to stand for 2 hours, a large amount of white precipitate appeared at the bottom of the solution. After filtration and recovery, it was characterized using infrared spectroscopy. Figure 4 As shown, the white precipitate is a high-purity EDTA ligand, and the calculated EDTA recovery rate is as high as 97%.

[0065] The above experimental results show that the Cu proposed in this invention... 0 / HCHO advanced reduction coupled acid precipitation technology can effectively recover metallic copper and EDTA ligands from Cu(II)-EDTA-containing wastewater.

[0066] Implementation Case 2

[0067] In Cu 0 In the / HCHO system, the initial pH of the reaction solution was adjusted to specified values ​​(10.0, 11.0, 12.0, 13.0, 14.0) using NaOH solution (10 mol / L) and H2SO4 solution (10 mol / L) to treat an 8 mM Cu(II)-EDTA solution. Other experimental conditions were the same as in Case 1. The Cu(II) removal effect before and after the reaction is as follows: Figure 5 As shown in the figure. Experimental results show that the removal efficiency of Cu(II) gradually increases with increasing pH value. Therefore, considering the economic cost and actual wastewater treatment effect, the optimal pH for the reaction is 13.0.

[0068] Implementation Case 3

[0069] Under the preferred condition of initial pH = 13.0, the Cu was changed 0 8 mM Cu(II)-EDTA solution was treated with dosages (0.6, 0.8, 1.0, 1.2, 1.4 g / L), with other experimental conditions the same as in Case 1. The Cu(II) removal effect before and after the reaction was as follows: Figure 6As shown in the figure. Experimental results show that as the amount of zero-valent copper added increases, the Cu(II) removal efficiency gradually improves. However, when Cu... 0 When the dosage exceeds 1.0 g / L, the improvement in Cu(II) removal rate is not significant. Therefore, considering the economic cost of treatment, Cu... 0 The optimal dosage is 1.0 g / L.

[0070] Implementation Case 4

[0071] At an initial pH of 13.0 and Cu 0 Under the preferred condition of a dosage concentration of 1.0 g / L, the initial molar ratio of HCHO to Cu(II)-EDTA was varied (10:1, 20:1, 30:1, 40:1, 50:1) to treat 8 mM Cu(II)-EDTA solutions, with other experimental conditions the same as in Case 1. Figure 7 The experimental results show that the higher the HCHO feed ratio, the higher the Cu(II) removal efficiency initially appears, followed by a decrease. These results indicate that when the initial molar ratio of HCHO to Cu(II)-EDTA is greater than 30, the Cu0 / HCHO system can completely remove Cu(II) from the Cu(II)-EDTA solution. However, further increasing the HCHO concentration does not further increase the Cu(II) removal efficiency. Considering both cost-effectiveness and treatment performance, an initial molar ratio of HCHO:Cu(II)-EDTA of 30 is selected as the optimal initial molar ratio for Cu(II) removal.

[0072] Implementation Case 5

[0073] At an initial pH of 13.0, Cu 0 Under the optimal conditions of an initial dosage of 1.0 mg / L and an initial molar ratio of HCHO to Cu(II)-EDTA of 30, Cu(II)-EDTA solutions with different initial concentrations (4, 6, 8, 10, 12 mM) were treated, with other experimental conditions the same as in Case Study 1. Figure 8 The experimental results show that Cu 0 The / HCHO system showed good removal efficiency for Cu(II)-EDTA solutions with different initial concentrations. Experimental results indicate that the Cu / HCHO system effectively removes Cu(II)-EDTA over a wide range of concentrations. 0 The HCHO system treatment yielded good results.

[0074] Implementation Case 6

[0075] At an initial pH of 13.0, Cu 0 The initial concentrations of HCHO and Cu(II)-EDTA were 1.0 g / L, 8 mM, and 240 mM, respectively. The study investigated common coexisting anions and cations (PO4) in the wastewater. 2- SO42- Cl - CO3 2- NO3 - Na + K + ) for Cu 0 The effect of HCHO advanced reduction method on the removal of Cu(II)-EDTA. For example... Figure 9 As shown, the coexistence of anions and cations had no significant inhibitory effect. The results indicate that Cu... 0 The / HCHO advanced reduction method has strong anti-interference ability in the recovery of metallic copper from Cu(II)-EDTA-containing wastewater.

[0076] In summary, this invention is based on Cu 0 The / HCHO advanced reduction method generates reducing active species hydrogen radical copper powder, and the formaldehyde advanced reduction method can achieve efficient complex breaking of Cu-EDTA in wastewater and efficient recovery of heavy metal copper. Calculations show that the copper recovery efficiency in the wastewater is close to 100%, and the copper ion content in the treated wastewater is below 0.05 mg / L. This treatment solution has advantages such as being green, efficient, low-cost, and highly resistant to interference, and has broad application prospects in the treatment of wastewater containing Cu(II)-EDTA complexes.

[0077] Without causing conflict, those skilled in the art can freely combine and use the above-mentioned additional technical features.

[0078] The above description is only a preferred embodiment of the present invention. Any technical solution that achieves the purpose of the present invention by using essentially the same means or by changing the amount of reaction reagents is within the protection scope of the present invention.

Claims

1. A process for efficient resource recovery of copper from Cu(II)-EDTA-containing wastewater, characterized in that: The process specifically includes the following steps: Step 1: Add an appropriate amount of formaldehyde to the Cu(II)-EDTA-containing wastewater to obtain a mixed system; Step 2: Adjust the pH of the mixture to the specified range; Step 3: Add an appropriate amount of copper powder to the mixture to catalyze the formation of hydrogen free radicals from formaldehyde; Step 4: Hydrogen radicals reduce and break the complex of Cu(II)-EDTA in the mixed system to generate elemental copper. After the reaction is completed, the mixture is allowed to stand and precipitate to achieve solid-liquid separation and recover elemental copper. The formaldehyde added in step 1 is commercial-grade formaldehyde, and the molar ratio of formaldehyde added to Cu(II) is 1:1 to 1:

50. The specified range in step 2 is: pH ≥ 11.0; In step 3, the amount of copper powder added is 0.1~2.0 g / L.

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