Graded recovery method for copper and arsenic in wastewater

Abstract

The invention relates to the technical field of industrial wastewater pollution treatment, in particular to a graded recovery method for copper and arsenic in wastewater. According to the method, the copper ions and the trivalent arsenic ions in the wastewater are respectively recovered by adopting sodium hydrosulfite under the condition of different pH values, so that the elementary substance copper and the elementary substance arsenic are obtained. According to the method, efficient graded recovery of copper and arsenic can be realized without introducing excessive substances; the treated wastewater can also reach the discharge standard, so that the effective treatment of the wastewater is realized; the method is simple to operate, high in efficiency, low in cost and wide in applicability.

Description

Technical Field

[0001] The present invention relates to the technical field of industrial wastewater pollution control, and more specifically, to a method for the hierarchical recovery of copper and arsenic in wastewater. Background Art

[0002] Many industrial sectors in China generate a large amount of wastewater containing copper and arsenic. Both copper and arsenic are highly biotoxic and must be removed before the wastewater is discharged. Currently, lime neutralization precipitation method and sulfide method are the most commonly used methods for treating wastewater. Among them, the principle of the lime neutralization method is to add calcium oxide (CaO) to form copper hydroxide, calcium arsenate, and calcium arsenite in the wastewater to achieve the purpose of removing copper and arsenic; however, the copper- and arsenic-containing waste residue generated by this method is difficult to treat and is prone to cause secondary pollution to the environment. The principle of removing copper and arsenic by the sulfide method is to add sodium sulfide or hydrogen sulfide to form copper sulfide (CuS) and arsenic sulfide (As 2 S 3 ) precipitates in the wastewater to achieve the removal of copper and arsenic; however, the value of arsenic sulfide precipitate is relatively low and it is difficult to achieve resource utilization. Moreover, its properties are unstable and it is easy to be oxidized to arsenic trioxide (As 2 O 3 ) under natural conditions, thus generating mixed hazardous waste. In short, the current methods for removing copper and arsenic from wastewater generate a large amount of hazardous waste that is difficult to treat, and there are defects such as the difficulty in recycling and resource utilization of copper and arsenic.

[0003] The price of elemental copper is 69,000 yuan per ton and it is widely used in the electrical, electronics industries, and alloy manufacturing industries. The price of elemental arsenic is 100,000 yuan per ton and it is a key raw material for manufacturing semiconductor materials (such as gallium arsenide and indium arsenide) and alloy materials. Therefore, efficiently hierarchically recovering copper and arsenic in wastewater and converting them into high-value elemental forms can not only avoid the generation of hazardous waste residues but also achieve the recovery of valuable elements. In view of this, the present invention provides a method for the hierarchical recovery of copper and arsenic in wastewater. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for the hierarchical recovery of copper and arsenic in wastewater.

[0005] The technical solution of the present invention for solving the above technical problem is as follows:

[0006] The present invention provides a method for the hierarchical recovery of copper and arsenic in wastewater, which uses sodium dithionite to separately recover copper ions and trivalent arsenic ions in the wastewater under different pH conditions to obtain elemental copper and elemental arsenic.

[0007] On the basis of the above technical solution, the present invention can also be improved as follows.

[0008] Further, it successively includes a copper recovery stage and an arsenic recovery stage. In the copper recovery stage, the pH value of the wastewater is 4, and in the arsenic recovery stage, the pH value of the wastewater is 2.

[0009] Further, in the copper recovery stage, the molar ratio of sodium dithionite to copper ions in the wastewater is 3 - 6:1.

[0010] Further, in the arsenic recovery stage, the molar ratio of sodium dithionite to arsenic ions in the wastewater is 1.5 - 2:1.

[0011] Further, it includes the following steps:

[0012] S1. Obtain the contents of copper ions and arsenic ions in the wastewater, and obtain the pH value of the wastewater;

[0013] S2. According to the pH value of the wastewater, add an acid solution or an alkali solution to the wastewater until the pH value of the wastewater is 4. Add sodium dithionite to the wastewater, stir and react, then filter, and separately collect the first filtrate and the first filter residue. Perform post-treatment on the first filter residue to obtain elemental copper;

[0014] S3. Add an acid solution to the first filtrate until the pH value of the first filtrate is 2. Add the sodium dithionite to the first filtrate, perform the first ultrasonic treatment and react, then filter, and separately collect the second filtrate and the second filter residue. Perform post-treatment on the second filter residue to obtain elemental arsenic.

[0015] Further, in step S2, the method of the stirring includes any one of magnetic stirring, mechanical stirring, and rotary mixing.

[0016] Further, the stirring frequency is 150 - 250 r / min, and the stirring time is 5 - 15 min.

[0017] Further, in step S3, the power of the first ultrasonic treatment is 100 - 500 W, and the time is 30 - 240 s.

[0018] Further, in step S3, the post-treatment of the second filter residue is to put the second filter residue into a carbon disulfide solution for the second ultrasonic treatment, filter and collect the third filter residue, and wash and dry the third filter residue.

[0019] Further, the power of the second ultrasonic treatment is 100 - 500 W, and the time is 10 - 60 min.

[0020] The beneficial effects of the present invention are:

[0021] (1) The method for the hierarchical recovery of copper and arsenic in wastewater of the present invention can achieve the efficient hierarchical recovery of copper and arsenic without introducing excessive substances;

[0022] (2) The method for the hierarchical recovery of copper and arsenic in wastewater of the present invention can efficiently remove more than 99.9% of arsenic in copper- and arsenic-containing wastewater and obtain high-purity elemental copper and arsenic products (>99.9%), realizing the resource recovery of copper and arsenic;

[0023] (3) The method for the hierarchical recovery of copper and arsenic in wastewater of the present invention can also make the treated wastewater meet the discharge standard, realizing the effective treatment of wastewater;

[0024] (4) The method for the hierarchical recovery of copper and arsenic in wastewater of the present invention is simple to operate, high in efficiency, low in cost and wide in applicability. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a schematic flow chart of the method for the hierarchical recovery of copper and arsenic in wastewater of the present invention;

[0026] Figure 2 is a picture of the elemental copper recovered in Example 1 of the method for the hierarchical recovery of copper and arsenic in wastewater of the present invention;

[0027] Figure 3 is an X-ray diffraction comparison chart of the elemental copper recovered in Example 1 of the method for the hierarchical recovery of copper and arsenic in wastewater of the present invention;

[0028] Figure 4 is an EDS composition analysis chart of the elemental copper recovered in Example 1 of the method for the hierarchical recovery of copper and arsenic in wastewater of the present invention;

[0029] Figure 5 is a picture of the elemental arsenic recovered in Example 1 of the method for the hierarchical recovery of copper and arsenic in wastewater of the present invention;

[0030] Figure 6 is an X-ray diffraction comparison chart of the elemental arsenic recovered in Example 1 of the method for the hierarchical recovery of copper and arsenic in wastewater of the present invention;

[0031] Figure 7 is an EDS composition analysis chart of the elemental arsenic recovered in Example 1 of the method for the hierarchical recovery of copper and arsenic in wastewater of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0032] The principles and features of the present invention will be described below with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0033] The method for the hierarchical recovery of copper and arsenic in wastewater of the present invention uses sodium dithionite (Na 2 S2 O 4 ) The copper ions and arsenic ions in the wastewater are respectively recovered under different pH conditions to obtain elemental copper and elemental arsenic.

[0034] The method for the hierarchical recovery of copper and arsenic in the wastewater of the present invention is based on the difference in the standard electrode potentials of copper ions and arsenic ions under different pH conditions, which causes the copper ions and arsenic ions to be successively reduced, thereby realizing the hierarchical recovery of copper and arsenic. This recovery method can achieve efficient hierarchical recovery without introducing too many substances, and the obtained elemental copper and elemental arsenic have high purity, enabling them to be effectively reused. At the same time, the treated wastewater can also meet the discharge standards, realizing the effective treatment of the wastewater.

[0035] Specifically, the hierarchical recovery method of the present invention successively includes a copper recovery stage and an arsenic recovery stage. In the copper recovery stage, the pH value of the wastewater is 4, and in the arsenic recovery stage, the pH value of the wastewater is 2.

[0036] Under the above conditions, the specific principle of the hierarchical recovery is based on the difference in standard electrode potentials, E 0 (Cu(II) / Cu(0)) = 0.34V > E 0 (As(III) / As(0)) = 0.24V, so copper ions are more easily reduced. Quantitatively adding Na 2 S 2 O 4 , first reduces the copper ions to elemental copper; under ultrasonic conditions, Na 2 S 2 O 4 can quickly decompose to generate SO 2 - free radicals. At the same time, the reaction of SO 2 - with H + will generate H· free radicals. The SO 2 - and H· free radicals react with As(III) to form elemental arsenic.

[0037] The above process can remove more than 99.9% of copper and arsenic in the wastewater, recover more than 99.5% of copper and arsenic in the wastewater, and obtain high-purity elemental copper and elemental arsenic products (the arsenic content is greater than 99.5 wt%), realizing the efficient removal and resource recovery of copper and arsenic.

[0038] Preferably, in the copper recovery stage, the molar ratio of sodium dithionite to copper ions in the wastewater is 3-6:1. Since side reactions occur during the reaction, setting the above molar ratio range can avoid waste of sodium dithionite and secondary pollution of the wastewater when the molar ratio of sodium dithionite to copper ions in the wastewater is greater than this range. When the molar ratio of sodium dithionite to copper ions in the wastewater is less than this range, the reaction will be incomplete, resulting in poor removal and / or recovery of copper ions, and only 30-70% of copper can be recovered.

[0039] Preferably, in the arsenic recovery stage, the molar ratio of sodium dithionite to arsenic ions in the wastewater is 1.5-2:1.

[0040] The method for the fractional recovery of copper and arsenic in the wastewater of the present invention comprises the following steps:

[0041] S1. Obtain the contents of copper ions and trivalent arsenic ions in the wastewater and the pH value of the wastewater.

[0042] The contents of copper ions and trivalent arsenic ions and the pH value of the wastewater can be obtained by conventional means.

[0043] S2. According to the pH value of the wastewater, add an acid solution or an alkali solution to the wastewater until the pH value of the wastewater is 4. Then add sodium dithionite to the wastewater, stir and react, and then filter. Collect the first filtrate and the first filter residue respectively, and perform post-treatment on the first filter residue to obtain elemental copper.

[0044] In this step, the main chemical reactions are shown in reaction formulas (1)-(3):

[0045] S 2 O 4 2- +2Cu 2+ +2H 2 O→Cu↓+2SO 3 2- +4H + Reaction formula (1)

[0046] 2S 2 O 4 2- +H 2 O→S 2 O 3 2- +2HSO 3 - Reaction formula (2)

[0047] 2S 2 O 4 2- +2H + →2SO 2+H 2 O+S 2 O 3 2- Reaction formula (3)

[0048] During the reaction process, the reaction process of reaction formula (1) is the main reaction, and the reaction processes of reaction formulas (2) and (3) are side reactions.

[0049] In this step, when the pH value of the wastewater is greater than 4, an acid solution is added to the wastewater; when the pH value of the wastewater is less than 4, an alkali solution is added to the wastewater. The acid solution can be one or more of H 2 SO 4 , HCl, HNO 3 , and the alkali solution can be NaOH.

[0050] Preferably, in this step, the stirring method includes any one of magnetic stirring, mechanical stirring, and rotary mixing.

[0051] Preferably, the stirring frequency is 150 - 250 r / min, and the stirring time is 5 - 15 min.

[0052] S3. Add an acid solution to the first filtrate until the pH value of the first filtrate is 2. Add sodium dithionite to the first filtrate, perform the first ultrasonic treatment and reaction, then filter, collect the second filtrate and the second filter residue respectively, and perform post-treatment on the second filter residue to obtain elemental arsenic.

[0053] In this step, the main chemical reactions are shown in reaction formulas (4) - (12):

[0054]

[0055] H 3 AsO 3 + 3H· → 3H 2 O + As↓ Reaction formula (8)

[0056]

[0057] 2H 2 S + SO 2 → 3 / 8S 8 ↓ + 2H 2 O Reaction formula (12)

[0058] During the reaction process, the reaction processes of reaction formulas (4) - (8) are the main reactions, and the reaction processes of reaction formulas (9) - (12) are side reactions.

[0059] Preferably, the acid solution used in this step can be H 2 SO4 , HCl, HNO 3 One or more of them.

[0060] Preferably, the power of the first ultrasonic treatment is 100 - 500 W and the time is 30 - 240 s; more preferably, the power of the first ultrasonic treatment is 200 - 400 W and the time is 40 - 120 s.

[0061] Preferably, in this step, the post-treatment of the second filter residue is to put the second filter residue into a carbon disulfide solution for the second ultrasonic treatment, filter and collect the third filter residue, and wash and dry the third filter residue. Since side reactions (9)-(12) will occur during the reaction, there will be trace amounts of elemental sulfur in the second filter residue. Therefore, the second filter residue is put into a carbon disulfide solution for ultrasonic treatment to dissolve the trace elemental sulfur and obtain high-purity elemental arsenic.

[0062] Preferably, the power of the second ultrasonic treatment is 100 - 500 W and the time is 10 - 60 min; more preferably, the time of the second ultrasonic treatment is 10 - 60 min, and even more preferably 20 - 30 min.

[0063] The specific process of the present invention is as Figure 1 shown. In addition, it should be noted that in the method of the present invention, washing means washing with water by a conventional method, the solid-liquid separation method is a combination of one or more of sand filtration, pressure filtration, membrane filtration and centrifugal separation, and drying is also a conventional drying method, and the specific temperature is not limited.

[0064] The present invention will be specifically described below through examples.

[0065] Example 1

[0066] The treatment method of the present invention is used to treat 500 mL of copper- and arsenic-containing wastewater. After testing, the pH value of the wastewater in this example is 3.2, the concentration of Cu(II) is 1201.1 mg / L, and the concentration of As(III) is 101.3 mg / L.

[0067] The specific steps of the fractional recovery in this example are as follows:

[0068] (1) Add an appropriate amount of NaOH to the wastewater to adjust the pH value of the wastewater to 4, add 6.92 g of Na 2 S 2 O 4 , and stir at a frequency of 200 r / min for 5 min at room temperature to obtain a solid-liquid mixture.

[0069] (2) The generated precipitate was separated by suction filtration, washed with water until neutral, and dried to obtain 0.587 g of recovered elemental copper. The Cu concentration in the solution was measured to be 0.5 mg / L by inductively coupled plasma optical emission spectrometer, and the removal rate of copper was 99.96%; the recovery rate was 97.83%.

[0070] (3) An appropriate amount of H 2 SO 4 was added to the filtrate to adjust the pH value of the filtrate to 2. Then 0.18 g of Na 2 S 2 O 4 was added, and under the condition of a power of 300 W, ultrasonic treatment was carried out for 40 s to obtain a solid-liquid mixture.

[0071] (4) The generated precipitate was separated by suction filtration, washed with water until neutral, and dried; the filter residue was put into 50 mL of CS 2 solution, and under the condition of a power of 200 W, ultrasonic treatment was carried out for 20 min, then solid-liquid separation was carried out, and it was washed 4 times with water and dried to obtain 0.048 g of elemental arsenic. The As concentration in the solution was measured to be 0.05 mg / L by atomic fluorescence spectrometer, the removal rate of arsenic was 99.95%, and the recovery rate was 96.00%.

[0072] Figure 2 This is a picture of the recovered elemental copper in this example. Figure 3 This is the X-ray diffraction comparison chart of the recovered elemental copper in this example. The spectrum above the diffraction chart is the elemental copper obtained in this example, and the corresponding spectrum below is the standard product of elemental copper.

[0073] By comparison, it can be found that the elemental copper spectrum obtained in this example is highly similar to the standard product spectrum, indicating that the elemental copper obtained in this example has a high purity.

[0074] The X-ray energy spectrum analysis (EDS) composition analysis of the recovered elemental copper is as Figure 4 shown. According to Figure 4 it can be seen that the purity of the elemental copper obtained in this example is 99.51 wt%, indicating that the elemental copper obtained in this example has a high purity and can be applied to fields such as electrical, light industry, machinery manufacturing, construction industry, and national defense industry.

[0075] Figure 5 This is a picture of the recovered elemental arsenic in this example. Figure 6 This is the X-ray diffraction comparison chart of the recovered elemental arsenic in this example. By comparing with the literature (Water Research 2022, 223, 118981), the elemental arsenic spectrum obtained in this example is highly similar to the XRD spectrum of amorphous elemental arsenic, indicating that the elemental arsenic obtained in this example has a high purity. The X-ray energy spectrum analysis (EDS) composition analysis of the recovered elemental arsenic is as Figure 7As shown, it indicates that the purity of the elemental arsenic obtained in this embodiment is 99.83 wt%, demonstrating that the elemental arsenic obtained in this embodiment has a high purity and can be used as a raw material for semiconductor materials.

[0076] Example 2

[0077] The treatment method of the present invention is used to treat 2 L of copper- and arsenic-containing wastewater. After testing, the pH value of the wastewater in this embodiment is 1.3, the content of Cu(II) is 565.6 mg / L, and the content of As(III) is 1237.5 mg / L.

[0078] The specific steps of the hierarchical recovery in this embodiment are as follows:

[0079] (1) Add an appropriate amount of NaOH to the wastewater to adjust the pH value of the wastewater to 4, and add 13.05 g of Na 2 S 2 O 4 , and stir at a frequency of 250 r / min for 6 min at room temperature to obtain a solid-liquid mixture.

[0080] (2) Filter and separate the generated precipitate, wash it with water until it is neutral, and dry it to obtain 1.11 g of recovered elemental copper. The concentration of Cu in the solution is measured by an inductively coupled plasma optical emission spectrometer to be 0.3 mg / L. The removal rate of copper is 99.95%, and the recovery rate is 98.13%.

[0081] (3) Add an appropriate amount of HNO 3 to the filtrate to adjust the pH value of the filtrate to 2, and add 9.69 g of Na 2 S 2 O 4 , and perform ultrasonic treatment for 50 s under the condition of a power of 350 W to obtain a solid-liquid mixture.

[0082] (4) Filter and separate the generated precipitate, wash it with water until it is neutral, and dry it; put the filter residue into 60 mL of CS 2 solution, perform ultrasonic treatment for 20 min under the condition of a power of 250 W, then separate the solid and liquid, wash it 4 times with water, and dry it to obtain 2.37 g of elemental arsenic. The concentration of As in the solution is measured by an atomic fluorescence spectrometer to be 0.03 mg / L. The removal rate of arsenic is 99.99%, and the recovery rate is 95.76%.

[0083] Example 3

[0084] The treatment method of the present invention is used to treat 10 L of copper- and arsenic-containing wastewater. After testing, the pH value of the wastewater in this embodiment is 4.8, the content of Cu(II) is 103.4 mg / L, and the content of As(III) is 7.9 mg / L.

[0085] The specific steps of the hierarchical recovery in this embodiment are as follows:

[0086] (1) Add an appropriate amount of H 2 SO 4 to the wastewater to adjust the pH value of the wastewater to 4, and add 14.91 g of Na 2 S 2 O 4 . Stir at a frequency of 200 r / min for 8 min at room temperature to obtain a solid-liquid mixture.

[0087] (2) Filter and separate the generated precipitate, wash it with water until it is neutral, and dry it to obtain 0.99 g of recovered elemental copper. The Cu concentration in the solution is measured by an inductively coupled plasma emission spectrometer to be 0.1 mg / L, the removal rate of copper is 99.90%, and the recovery rate is 95.74%.

[0088] (3) Add an appropriate amount of H 2 SO 4 to the filtrate to adjust the pH value of the filtrate to 2, and add 0.35 g of Na 2 S 2 O 4 . Under the condition of a power of 400 W, perform ultrasonic treatment for 70 s to obtain a solid-liquid mixture.

[0089] (4) Filter and separate the generated precipitate, wash it with water until it is neutral, and dry it; put the filter residue into 40 mL of CS 2 solution, perform ultrasonic treatment for 25 min under the condition of a power of 200 W, then separate the solid and liquid, wash it 4 times with water, and dry it to obtain 76 mg of elemental arsenic. The As concentration in the solution is measured by an atomic fluorescence spectrometer to be 0.02 μg / L, the removal rate of arsenic is 99.99%, and the recovery rate is 96.20%.

[0090] Example 4

[0091] Use the treatment method of the present invention to treat 20 L of copper- and arsenic-containing wastewater. After testing, the pH value of the wastewater in this example is 0.8, the content of Cu(II) is 59.2 mg / L, and the content of As(III) is 983.9 mg / L.

[0092] The specific steps of the fractional recovery in this example are as follows:

[0093] (1) Add an appropriate amount of NaOH to the wastewater to adjust the pH of the wastewater to 4, and add 17.07 g of Na 2 S 2 O 4 . Stir at a frequency of 250 r / min for 10 min at room temperature to obtain a solid-liquid mixture.

[0094] (2) The generated precipitate was separated by suction filtration, washed with water until neutral, and dried to obtain 1.18 g of recovered elemental copper. The Cu concentration in the solution was determined to be 0.05 mg / L by an inductively coupled plasma optical emission spectrometer. The removal rate of copper was 99.92%, and the recovery rate was 99.32%.

[0095] (3) An appropriate amount of H 2 SO 4 was added to the filtrate to adjust the pH value of the filtrate to 2. 86.65 g of Na 2 S 2 O 4 was added, and the mixture was ultrasonically treated for 120 s under the condition of a power of 400 W to obtain a solid-liquid mixture.

[0096] (4) The generated precipitate was separated by suction filtration, washed with water until neutral, and dried. The filter residue was put into 500 mL of CS 2 solution, and ultrasonically treated for 30 min under the condition of a power of 200 W. Then, solid-liquid separation was carried out, and it was washed 4 times with water and dried to obtain 18.97 g of elemental arsenic. The As concentration in the solution was determined to be 0.11 mg / L by an atomic fluorescence spectrometer. The removal rate of arsenic was 99.99%, and the recovery rate was 96.39%.

[0097] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for graded recovery of copper and arsenic in wastewater, characterized in that: Sodium dithionite is used to recover copper ions and trivalent arsenic ions in wastewater under different pH conditions to obtain elemental copper and elemental arsenic.

2. The method for graded recovery of copper and arsenic in wastewater according to claim 1, characterized in that: The recovery method comprises a copper recovery stage and an arsenic recovery stage in sequence. In the copper recovery stage, the pH value of the wastewater is 4, and in the arsenic recovery stage, the pH value of the wastewater is 2.

3. The method for graded recovery of copper and arsenic in wastewater according to claim 2, characterized in that: In the copper recovery stage, the molar ratio of sodium dithionite to copper ions in the wastewater is 3-6:

1.

4. The method for graded recovery of copper and arsenic in wastewater according to claim 2, characterized in that: In the arsenic recovery stage, the molar ratio of sodium dithionite to arsenic ions in the wastewater is 1.5-2:

1.

5. A method for graded recovery of copper and arsenic in wastewater according to any one of claims 2 to 4, characterized in that: The following steps are involved: S1. Obtaining the contents of copper ions and trivalent arsenic ions in the wastewater, and obtaining the pH value of the wastewater; S2. According to the pH value of the waste water, an acid solution or an alkaline solution is added to the waste water until the pH value of the waste water is 4, sodium dithionite is added to the waste water, stirred and reacted, and then filtered, a first filtrate and a first filter residue are collected respectively, and the first filter residue is post-treated to obtain elemental copper; S3. Add an acid solution to the first filtrate until the pH value of the first filtrate reaches 2, add the sodium dithionite to the first filtrate, perform a first ultrasonic treatment and filter after the reaction, collect a second filtrate and a second filter residue respectively, and post-treat the second filter residue to obtain elemental arsenic.

6. The method for graded recovery of copper and arsenic in wastewater according to claim 5, characterized in that: In step S2, the stirring method includes any one of magnetic stirring, mechanical stirring and rotation mixing.

7. The method for graded recovery of copper and arsenic in wastewater according to claim 6, characterized in that: The stirring frequency is 150-250 r / min, and the stirring time is 5-15 min.

8. The method for graded recovery of copper and arsenic in wastewater according to claim 5, characterized in that: In step S3, the power of the first ultrasonic treatment is 100 to 500 W, and the time is 30 to 240 s.

9. The method for graded recovery of copper and arsenic in wastewater according to claim 5, characterized in that: In step S3, the post-treatment of the second filter residue is to place the second filter residue in a carbon disulfide solution for a second ultrasonic treatment, filter and collect the third filter residue, and wash and dry the third filter residue.

10. The method for graded recovery of copper and arsenic in wastewater according to claim 9, characterized in that: The power of the second ultrasonic treatment is 100-500W, and the time is 10-60min.

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