Combined treatment method for acidic wastewater

Abstract

The present invention relates to the technical field of wastewater treatment. Disclosed is a combined treatment method for acidic wastewater. The combined treatment method for acidic wastewater comprises: introducing acidic wastewater generated during an industrial process into an electrochemical device and performing an electrochemical treatment on the acidic wastewater for neutralization and heavy metal extraction, wherein an anode of the electrochemical device is loaded with a non-metallic mineral material; and introducing an electrochemically treated solution into a sedimentation tank where carbon dioxide is captured from the air and fixed, and then directly discharging a treated solution conforming to "Environmental Quality Standards for Surface Water". The present invention relates to an acidic wastewater treatment method that is simple, efficient, and easy to operate and also achieves recovery of heavy metals. By introducing a readily available and environmentally friendly non-metallic mineral at the anode of the electrochemical device, hydrogen ions released during electrolysis are consumed, thereby reducing inhibition of heavy metal deposition by hydrogen ions and increasing the extraction rate of heavy metals from wastewater. The electrochemically treated solution then captures and fixes carbon dioxide, enabling direct discharge of the treated solution.

Description

A combined treatment method for acidic wastewater Technical Field

[0001] This invention relates to the field of wastewater treatment technology, and in particular to a combined treatment method for acidic wastewater. Background Technology

[0002] Acidic wastewater mainly originates from human activities such as chemical processing, electroplating, metal smelting, and mining. Statistics show that billions to tens of billions of cubic meters of acidic wastewater are generated globally each year. Its high acidity and strong corrosiveness easily damage pipelines and infrastructure, and it contains high concentrations of highly toxic heavy metals such as copper, cadmium, and zinc. If this wastewater is discharged indiscriminately or improperly treated, it will severely impair the environment's self-purification capacity, negatively impact biological growth, and lead to the waste of large amounts of valuable metal resources (such as copper, cadmium, and zinc). Currently common treatment methods include neutralization precipitation, ion exchange, membrane separation, and biological treatment. However, these methods are costly, inefficient, prone to secondary pollution, and unable to effectively recover metal resources from wastewater, which is inconsistent with modern sustainable development principles. For example, the widely used neutralization method usually requires the addition of expensive chemical reagents and generates large amounts of sludge containing heavy metals, leading to secondary pollution and waste of metal resources. In recent years, electrochemical methods have attracted much attention as an emerging technology for treating acidic wastewater. Through electrolysis, it achieves neutralization and heavy metal removal from wastewater, exhibiting high selectivity and environmental friendliness. However, traditional electrochemical methods for treating acidic wastewater suffer from problems such as complex design, low efficiency, and high energy consumption, becoming one of the bottlenecks in technological development. For example, the existing technology (CN117865291A) treats acidic wastewater using an electrochemical membrane reactor, achieving neutralization and heavy metal removal, but the process is complex and requires additional costs for membrane configuration and replacement. The existing technology (CN116282400A) treats acidic wastewater using a dual-pulse low-voltage electrocoagulation method, achieving acid neutralization and co-precipitation removal of heavy metal chromium, but this process increases the difficulty of subsequent heavy metal recovery.

[0003] Therefore, existing technologies still need to be improved and developed. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the purpose of this invention is to provide a combined treatment method for acidic wastewater, which aims to solve the problems of high cost, low treatment efficiency, easy secondary pollution, and inability to effectively recover metal resources in wastewater by existing acidic wastewater treatment methods.

[0005] The technical solution of the present invention is as follows:

[0006] This invention provides a combined treatment method for acidic wastewater, comprising the following steps:

[0007] Acidic wastewater generated during industrial processes is fed into an electrochemical device. The anode of the electrochemical device is loaded with non-metallic mineral materials, and the acidic wastewater is neutralized and heavy metals are extracted through electrochemical treatment.

[0008] The electrochemically treated solution is fed into a sedimentation tank to capture and fix carbon dioxide in the air, resulting in a treated solution that meets the "Surface Water Environmental Quality Standard" and is then directly discharged.

[0009] Optionally, the acidic wastewater has a pH of 1-5, a copper ion concentration of 10-200 mg / L, a cadmium ion concentration of 2-200 mg / L, and a zinc ion concentration of 15-300 mg / L.

[0010] Optionally, the non-metallic mineral material is selected from one or more of limestone, dolomite, magnesia, wollastonite, olivine, and phosphogypsum.

[0011] Optionally, the non-metallic mineral material is limestone particles with a particle size of 0.1-10 cm.

[0012] Optionally, the electrochemical treatment conditions are: rated voltage of 2-15V, rated current of 10-100mA, and time of 1-15h.

[0013] Optionally, in the extraction of the heavy metals, the extraction rate of copper is 99.3%-99.5%, the extraction rate of cadmium is 95.2%-99.1%, and the extraction rate of zinc is 90.9%-95.1%.

[0014] The combined treatment method for acidic wastewater, wherein the step of entering the electrochemically treated solution into a sedimentation tank to capture and fix carbon dioxide in the air specifically involves: the electrochemically treated solution is alkaline, and after entering the air-exposed sedimentation tank, the carbon dioxide in the air dissolves in the alkaline solution and reacts with calcium or magnesium ions to form calcium carbonate or magnesium carbonate precipitates, thereby capturing and fixing the carbon dioxide, so that the final treated solution meets the "Surface Water Environmental Quality Standard" before being directly discharged.

[0015] Optionally, the pH value of the solution after electrochemical treatment is 7.0 to 10.5, and the concentration of calcium or magnesium ions is ≥2mM.

[0016] Optionally, in the solution after electrochemical treatment, the concentration of Cu ions is ≤0.01 mg / L, the concentration of Cd ions is ≤0.01 mg / L, and the concentration of Zn ions is ≤0.01 mg / L.

[0017] Optionally, the pH value of the treatment solution after carbon dioxide capture and fixation is 6.0-9.0. Beneficial effects:

[0018] This invention provides a simple, efficient, and easy-to-operate combined treatment method for acidic wastewater that enables heavy metal recovery and carbon dioxide capture and fixation. By introducing inexpensive, readily available, and environmentally friendly non-metallic mineral materials into an electrochemical device and fixing them near the anode using a barrier, this method efficiently and continuously consumes hydrogen ions generated by the wastewater and the anode during electrochemical treatment. This reduces the inhibition of heavy metal deposition by hydrogen ions, thereby enhancing the recovery of heavy metals from the wastewater. The solution after electrochemical treatment is alkaline, and combined with the high concentration of calcium and magnesium ions released by the non-metallic minerals, it can directly capture carbon dioxide from the air, forming precipitates for fixation. The resulting treated solution meets the "Surface Water Environmental Quality Standards." Compared with existing acidic wastewater treatment technologies, this invention is simple and convenient to operate, achieving neutralization of acidic wastewater and in-situ recovery of heavy metals under single-reaction equipment conditions, and also realizing carbon fixation, demonstrating significant environmental benefit potential. Attached Figure Description

[0019] Figure 1 is a schematic flowchart of the acidic wastewater treatment method provided by the present invention.

[0020] Figure 2 is a schematic diagram of the electrochemical device used in the acidic wastewater treatment method of the present invention.

[0021] Figure 3 shows the results of heavy metal extraction from acidic wastewater after electrochemical treatment in Example 1 of this invention.

[0022] Figure 4 shows the cadmium extraction rate results of acidic wastewater with different initial cadmium ion concentrations after electrochemical treatment in Example 2 of the present invention.

[0023] Figure 5 shows the cadmium extraction rate results after electrochemical treatment of acidic wastewater with different initial pH values ​​in Example 3 of the present invention.

[0024] Figure 6 shows the changes in the concentration of each heavy metal ion, the change in pH value, and the extraction of each heavy metal after electrochemical treatment of the acidic wastewater discharged from the mine in Example 4 of the present invention.

[0025] Figure 7 shows the results of pH changes, heavy metal extraction, and carbon dioxide capture and fixation of the final treated liquid after combined treatment of acidic wastewater in Example 5 of the present invention.

[0026] Figure 8 shows the results of heavy metal extraction rate and carbon dioxide capture and fixation of acidic wastewater after combined treatment in Example 6 of the present invention. Detailed Implementation

[0027] This invention provides a combined treatment method for acidic wastewater. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention.

[0028] Unless otherwise defined, 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 invention pertains. The terminology used herein in the description of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0029] This invention provides a combined treatment method for acidic wastewater, comprising the following steps:

[0030] S1. Acidic wastewater generated during industrial processes is fed into an electrochemical device, wherein the anode of the electrochemical device is loaded with non-metallic mineral materials, and the acidic wastewater is neutralized and heavy metals are extracted through electrochemical treatment.

[0031] S2. The electrochemically treated solution is introduced into a sedimentation tank to capture and fix carbon dioxide in the air, resulting in a treated solution that meets the "Surface Water Environmental Quality Standard" and is then directly discharged.

[0032] In step S1, in some embodiments, the acidic wastewater has a pH value of 1-5, a copper ion concentration of 10-200 mg / L, a cadmium ion concentration of 2-200 mg / L, and a zinc ion concentration of 15-300 mg / L.

[0033] In some embodiments, the non-metallic mineral material is selected from one or more of limestone, dolomite, magnesia, wollastonite, olivine, and phosphogypsum. The non-metallic mineral material may be derived from natural minerals or solid waste.

[0034] In some embodiments, the non-metallic mineral material is limestone particles with a particle size of 0.1-10 cm.

[0035] In some embodiments, the electrochemical treatment conditions are: rated voltage of 2-15V, rated current of 10-100mA, and time of 1-15h.

[0036] Water electrolysis technology uses direct current to decompose water into hydrogen and oxygen, releasing hydrogen ions and hydroxide ions at the anode and cathode. The hydroxide ions released at the cathode consume the acidity (hydrogen ions) in the wastewater, raising the pH value of acidic wastewater. Simultaneously, the negatively charged cathode attracts heavy metal cations, depositing them on the electrode surface through electron transfer and localized high pH. However, during electrolysis, the hydrogen ions released at the anode consume the hydroxide ions generated at the cathode and compete with heavy metals for electrons, leading to reduced wastewater neutralization efficiency and heavy metal extraction efficiency. Therefore, traditional electrochemical technologies typically require high energy consumption and complex structures and operating methods. This invention provides an electrochemical treatment method for acidic wastewater that utilizes limestone, a cheap, readily available, and environmentally friendly natural mineral widely used in acidic wastewater treatment. By fixing the limestone near the anode as a barrier, an integrated electrochemical device is formed. This device efficiently and continuously consumes the wastewater and hydrogen ions released from the anode during electrolysis, causing hydroxide ions generated at the cathode to accumulate in the solution, increasing the pH of the wastewater solution. This reduces the inhibition of heavy metal deposition by hydrogen ions during electrochemical processes, enhancing the recovery of heavy metals from the wastewater. Higher applied current and voltage result in higher treatment efficiency. For wastewater with high pollutant concentrations, the treatment rate can be accelerated by increasing the current and voltage; for wastewater with low concentrations, the voltage and current can be reduced to decrease energy consumption.

[0037] In some embodiments, the extraction rates of copper, cadmium, and zinc are 99.3%-99.5%, 95.2%-99.1%, and 90.9%-95.1%, respectively, during the extraction of the heavy metals.

[0038] In step S2, in some embodiments, the step of entering the electrochemically treated solution into a sedimentation tank to capture and fix carbon dioxide in the air specifically involves: the electrochemically treated solution is alkaline, and after entering the air-exposed sedimentation tank, the carbon dioxide in the air dissolves in the alkaline solution and reacts with calcium or magnesium ions to form calcium carbonate or magnesium carbonate precipitates, thereby capturing and fixing the carbon dioxide. After the final treated solution meets the "Surface Water Environmental Quality Standard", it is directly discharged.

[0039] In some embodiments, the pH of the electrochemically treated solution is 7.0 to 10.5, and the concentration of calcium or magnesium ions is ≥2 mM.

[0040] In some embodiments, the concentrations of Cu ions, Cd ions, and Zn ions in the electrochemically treated solution are ≤0.01 mg / L, ≤0.01 mg / L, and ≤0.01 mg / L, respectively. According to the Class V standard limits of the "Surface Water Environmental Quality Standard" (GB 3838-2002), the limits are: copper 1 mg / L, zinc 2.0 mg / L, and cadmium 0.01 mg / L. The standard for judging the effluent is that the electrochemical treatment ends when the heavy metal ion concentrations in the wastewater decrease to the corresponding environmental quality standard concentrations. Therefore, it can be seen that the treated solution obtained after the combined treatment of acidic wastewater in this invention meets the standards for direct discharge.

[0041] In some embodiments, the pH of the treatment solution after carbon dioxide capture and fixation is 6.0-9.0.

[0042] The following detailed description uses specific examples.

[0043] Example 1

[0044] Figure 1 shows the flow chart for acidic wastewater treatment. The treatment methods include electrochemical treatment and carbon dioxide capture and fixation. The electrochemical treatment utilizes an integrated electrochemical reactor, as shown in Figure 2. This integrated electrochemical reactor consists of four parts: a ruthenium-iridium plated rod-shaped titanium anode, industrial-grade granular limestone particles (particle size: 0.1-10 cm), a porous barrier for filling with limestone, and a stainless steel cathode. The anode is installed in the middle of the barrier, with limestone particles directly filling the barrier around the anode. The cathode is installed outside the barrier. The limestone particles are loaded onto the anode of the electrochemical reactor.

[0045] The specific steps for the electrochemical treatment of acidic wastewater are as follows:

[0046] Acidic wastewater is pumped into an integrated electrochemical reactor. A direct current (DC) of 3V and 20mA is applied to the reactor for electrochemical treatment for 5 hours. The initial pH of the acidic wastewater is 1.5, and the concentrations of the metal ions present are: Cu 10 mg / L, Cd 2 mg / L, Zn 300 mg / L, and Ca 73 mg / L.

[0047] During the processing, samples were taken to test various parameters of the solution. The test results are shown in Table 1 below:

[0048] Table 1

[0049] Heavy metals were deposited at the cathode in the electrochemical device, and the deposition mass of each heavy metal is shown in Table 2:

[0050] Table 2

[0051] Table 1 shows that the solution treated electrochemically in this embodiment had a pH of 7.8, while the concentration of heavy metals was significantly reduced to Cu ≤ 0.01 mg / L, Cd ≤ 0.01 mg / L, and Zn ≤ 0.01 mg / L, achieving zero pollution emissions. Simultaneously, heavy metals were deposited at the cathode. The extraction rates of each heavy metal were calculated based on the deposition mass at the cathode of the electrochemical device, as shown in Figure 3. The results indicate that the electrochemical treatment in this embodiment achieved a copper extraction rate of 99.5%, a cadmium extraction rate of 95.8%, and a zinc extraction rate of 90.9%.

[0052] The extraction rate is calculated as follows: Heavy metal extraction rate (%) = mass of heavy metals deposited at the cathode / (volume of treated wastewater * initial concentration of heavy metal ions in the wastewater).

[0053] Example 2

[0054] Electrochemical treatment of acidic wastewater with different initial cadmium ion concentrations

[0055] First, three simulated acidic wastewater solutions with a pH of 3.0 and cadmium ion concentrations of 2, 20, and 200 mg / L were selected. Then, under the condition of providing an external constant current power supply (rated voltage 3V, rated current 20mA), electrochemical treatment was carried out for 2.5, 4, and 8 hours, respectively, and the pH value change and cadmium extraction of the solutions after electrochemical treatment were tested.

[0056] As shown in Figure 4, this embodiment improved the pH of acidic wastewater containing three different cadmium concentrations from 3.0 to 8.4, 9.7 and 9.3 respectively through electrochemical treatment, and achieved cadmium extraction rates of 95.2%, 96.8% and 98.0% respectively.

[0057] The extraction rate is calculated as follows: Heavy metal extraction rate (%) = mass of heavy metals deposited at the cathode / (volume of treated wastewater * initial concentration of heavy metal ions in the wastewater).

[0058] Example 3

[0059] Electrochemical treatment of acidic wastewater with different initial pH values

[0060] Solutions with initial pH values ​​of 2.0, 3.0, and 4.0, and a cadmium ion concentration of 20 mg / L were selected as simulated acidic wastewater. Under the condition of providing an external constant current power supply (rated voltage 3V, rated current 20mA), the solutions were treated for 15, 4, and 2.5 hours, respectively, and the pH value changes and cadmium extraction were tested after electrochemical treatment.

[0061] As shown in Figure 5, this embodiment improved the pH of three different wastewaters from 2.0 to 7.8, from 3.0 to 9.7, and from 4.0 to 10.1 through electrochemical treatment, respectively, and achieved cadmium extraction rates of 98.0%, 96.8%, and 95.3%, respectively.

[0062] The extraction rate is calculated as follows: Heavy metal extraction rate (%) = mass of heavy metals deposited at the cathode / (volume of treated wastewater * initial concentration of heavy metal ions in the wastewater).

[0063] Example 4

[0064] The difference between this embodiment and embodiment 5 is that: the wastewater from a mining area in Shaoguan City, Guangdong Province was selected as the treatment object. After electrochemical treatment for 10 hours under the condition of providing an external constant current power supply (rated voltage 3V, rated current 20mA), the changes in the concentration of heavy metal ions, the changes in pH value, and the extraction of each heavy metal in the wastewater solution after electrochemical treatment were tested. The test results are shown in Figure 6.

[0065] As shown in Figure 6a, the electrochemical treatment in this embodiment can effectively remove heavy metal ions such as copper, cadmium, and zinc from wastewater. Simultaneously, the electrochemical treatment can raise the pH of the wastewater from 2.5 to 7.8 (as shown in Figure 6b). Furthermore, based on the mass of heavy metals deposited at the cathode in the electrochemical device, a copper extraction rate of 99.5%, a cadmium extraction rate of 95.8%, and a zinc extraction rate of 90.9% were achieved (as shown in Figure 6c).

[0066] The extraction rate is calculated as follows: Heavy metal extraction rate (%) = mass of heavy metals deposited at the cathode / (volume of treated wastewater * initial concentration of heavy metal ions in the wastewater).

[0067] Example 5

[0068] Combined treatment of acidic wastewater containing multiple heavy metal ions

[0069] Experimental group:

[0070] (1) Electrochemical treatment

[0071] An integrated electrochemical reaction device was selected to simulate acidic wastewater by using a solution containing 20 mg / L of copper, cadmium, and zinc ions at pH 3.0. Electrochemical treatment was carried out for 4 hours under the condition of providing an external constant current power supply (rated voltage 3V, rated current 20mA).

[0072] (2) Capture and fix carbon dioxide

[0073] The specific steps are as follows: The alkaline solution, which has undergone electrochemical treatment, is pumped into the sedimentation tank and comes into direct contact with the air. The high concentration of hydroxide ions accelerates the dissolution of carbon dioxide in the air and reacts with calcium ions in the solution to form calcium carbonate precipitate. After the carbon dioxide capture and fixation reaction, the hydroxide concentration in the solution decreases and the pH of the solution drops to 7.8, meeting the "Surface Water Environmental Quality Standard", and is then directly discharged.

[0074] Control group:

[0075] The control group used a conventional electrochemical device (without calcium carbonate mineral particles at the anode). A solution containing 20 mg / L copper, cadmium, and zinc ions at pH 3.0 was introduced into the conventional electrochemical reactor as a control. Electrochemical treatment was performed for 4 hours, and then the pH change and heavy metal extraction were tested before and after the acidic wastewater was treated.

[0076] The pH changes and heavy metal extraction of the two treated wastewater solutions are shown in Figures 7a and 7b. The results show that the electrochemical treatment method used in this embodiment effectively increases the wastewater pH to 9.3, while achieving copper extraction rates of 99.5%, cadmium extraction rates of 99.0%, and zinc extraction rates of 94.2%. The extraction rate is calculated as follows: Heavy metal extraction rate (%) = Mass of heavy metals deposited at the cathode / (Volume of treated wastewater * Initial concentration of heavy metal ions in the wastewater). As shown in Figure 7c, the captured and fixed carbon dioxide concentration reached 11.2 mg / L. Specific test data are shown in Tables 3 and 4.

[0077] Table 3

[0078] Table 4

[0079] Example 6

[0080] (1) Electrochemical treatment

[0081] The specific steps are as follows: acidic wastewater (pH value 3.0, heavy metal ion concentration (Cu 200mg / L, Cd 200mg / L, Zn 15mg / L), inorganic carbon content 0.2mg / L) is pumped into an integrated electrochemical reactor. The anode of the electrochemical reactor is loaded with limestone particles (particle size: 0.1-10cm). The electrochemical reactor is powered by a DC power supply with a rated voltage of 3V and a rated current of 20mA, and the electrochemical treatment is carried out for 4 hours.

[0082] (2) Capture and fix carbon dioxide

[0083] The specific steps are as follows: The electrochemically treated alkaline solution is pumped into the sedimentation tank and comes into direct contact with the air. The high concentration of hydroxide ions accelerates the dissolution of carbon dioxide in the air and reacts with calcium ions in the solution to form calcium carbonate precipitate. After the carbon dioxide capture and fixation reaction, the hydroxide concentration in the solution decreases and the pH of the solution drops to 8.0, meeting the "Surface Water Environmental Quality Standard", and is then directly discharged.

[0084] Sampling tests were conducted during the processing, and the test results are shown in Table 5 below:

[0085] Table 5

[0086] Heavy metals were deposited at the cathode in the electrochemical device, and the deposition mass of each heavy metal is shown in Table 6:

[0087] Table 6

[0088] As can be seen from Table 5, after electrochemical treatment, the pH of the solution increased to 9.4, and the concentrations of heavy metal ions decreased to 0.01 mg / L for Cu, 0.01 mg / L for Cd, and 0.01 mg / L for Zn, which meet the "Surface Water Environmental Quality Standard". The calcium ion concentration was above 92 mg / L.

[0089] After combined treatment, the discharged wastewater solution maintained a pH of 8.0, while the concentration of heavy metal ions was significantly reduced, achieving Cu ≤ 0.01 mg / L, Cd ≤ 0.01 mg / L, and Zn ≤ 0.01 mg / L, thus realizing zero-pollution discharge of acidic wastewater. Simultaneously, it achieved extraction rates as high as 99.3% for copper, 99.1% for cadmium, and 95.1% for zinc, as shown in Figure 8a. The extraction rate was calculated as follows: Heavy metal extraction rate (%) = Mass of heavy metals deposited at the cathode / (Volume of treated wastewater * Initial heavy metal ion concentration in the wastewater).

[0090] Based on the changes in inorganic carbon content, as shown in Figure 8b, the total carbon dioxide captured and fixed in the solution after electrochemical treatment was 9.6 mg / L. This indicates that the acidic wastewater treated by the combined method of this invention not only removes and recovers harmful heavy metal elements but also has good potential for carbon dioxide fixation.

[0091] It should be understood that the application of the present invention is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A combined treatment method of acidic waste water, characterized by, The method comprises the steps of: passing the acid wastewater generated in the industrial process into an electrochemical device, wherein the anode of the electrochemical device is loaded with non-metallic mineral materials, and the acid wastewater is neutralized and heavy metal is extracted through electrochemical treatment; passing the solution after electrochemical treatment into a precipitation tank, capturing and fixing carbon dioxide in the air to obtain a treated solution meeting the Surface Water Environmental Quality Standard for direct discharge.

2. The combined treatment method of acid waste water according to claim 1, characterized by, The acid wastewater has a pH value of 1-5, a copper ion concentration of 10-200 mg / L, a cadmium ion concentration of 2-200 mg / L, and a zinc ion concentration of 15-300 mg / L.

3. The combined treatment method of acid waste water according to claim 1, characterized by, The non-metallic mineral material is selected from one or more of limestone, dolomite, magnesite, wollastonite, olivine and phosphogypsum.

4. The combined treatment method of acid waste water according to claim 1, characterized by, The non-metallic mineral material is limestone particles with a particle size of 0.1-10 cm.

5. The combined treatment method of acid waste water according to claim 1, characterized by, The electrochemical treatment is performed under the conditions of a rated voltage of 2-15 V, a rated current of 10-100 mA, and a time of 1-15 h.

6. The method of electrochemical treatment of acid wastewater according to claim 1, characterized in that, In the extraction of heavy metals, the extraction rate of copper is 99.3%-99.5%, the extraction rate of cadmium is 95.2%-99.1%, and the extraction rate of zinc is 90.9%-95.1%.

7. The combined treatment method of acid waste water according to claim 1, characterized by, The step of capturing and fixing carbon dioxide in the air after the electrochemical treatment of the solution is specifically as follows: the solution after electrochemical treatment is alkaline, and after entering the precipitation tank exposed to air, carbon dioxide in the air is dissolved in the alkaline solution and reacts with calcium or magnesium ions to form calcium carbonate or magnesium carbonate precipitate, thereby capturing and fixing carbon dioxide, so that the final treated solution meets the Surface Water Environmental Quality Standard and is directly discharged.

8. The combined treatment method of acidic waste water according to claim 7, characterized in that, The solution after electrochemical treatment has a pH value of 7.0-10.5 and a calcium ion or magnesium ion concentration of ≥2 mM.

9. The combined treatment method of acidic waste water according to claim 7, characterized in that, In the solution after electrochemical treatment, the Cu ion concentration is ≤0.01 mg / L, the Cd ion concentration is ≤0.01 mg / L, and the Zn ion concentration is ≤0.01 mg / L.

10. The combined treatment method of acidic waste water according to claim 7, characterized in that, The treated solution after capturing and fixing carbon dioxide has a pH value of 6.0-9.0.

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