Treatment method of chemical nickel wastewater

Abstract

The invention relates to the technical field of wastewater treatment, and particularly discloses a treatment method of chemical nickel wastewater. The invention relates to a chemical nickel wastewater treatment method, which comprises: aeration treatment: introducing chemical nickel wastewater into a pH value adjusting tank, adding Ca (OH) 2, adjusting the pH value to 11-12, and carrying out aeration treatment with the aeration rate of 10-15 m < 3 > / m < 2 > h and the aeration time of 90-120 min; fenton treatment: introducing the chemical nickel wastewater subjected to aeration treatment into a pH regulating tank, regulating the pH value, and then sequentially carrying out primary Fenton treatment, coagulating sedimentation treatment and secondary Fenton treatment. By adopting the treatment method of the chemical nickel wastewater, the minimum contents of nickel, phosphorus and COD (Chemical Oxygen Demand) in the wastewater are 0.035 mg / L, 0.159 mg / L and 9.31 mg / L, the removal rates of nickel, phosphorus and COD are as high as 99.97%, 99.85% and 99.79%, and the removal effect is improved.

Description

Technical Field

[0001] The present application relates to the technical field of wastewater treatment, and more specifically, to a method for treating chemical nickel wastewater. Background Art

[0002] Nickel is widely used in electroless plating, stainless steel, and battery production. Nickel is a heavy metal, classified as a Class I pollutant by the government. Its toxicity and bioaccumulation pose significant threats to the environment and human health, making it a key pollutant in wastewater. This makes the treatment of chemical nickel wastewater a crucial component of modern industrial pollution prevention and control. Nickel in nickel-containing wastewater from the electroless nickel plating process often forms stable complexes with ammonia nitrogen and organic chelating agents, making it challenging to treat.

[0003] In the related art, chemical precipitation method is commonly used to treat chemical nickel wastewater, that is, hydroxide or sulfide is used as a precipitant to remove nickel by generating Ni(OH)2 or NiS precipitation. However, this method is sensitive to pH value and Ni in the complex system is 2 + It is ineffective due to strong chelation. At the same time, there is a large amount of hypophosphite in chemical nickel wastewater, which makes subsequent treatment more difficult, the treatment effect is poor and the efficiency is low, which makes it difficult to meet the actual treatment needs of chemical nickel wastewater. Summary of the Invention

[0004] In order to improve the treatment efficiency and effect of chemical nickel wastewater treatment and reduce the treatment cost, the present application provides a method for treating chemical nickel wastewater.

[0005] In a first aspect, the present application provides a method for treating chemical nickel wastewater, which adopts the following technical solution: A method for treating chemical nickel wastewater, wherein the chemical nickel wastewater is derived from washing wastewater in a chemical nickel plating process, and the method for treating the chemical nickel wastewater comprises the following steps: Aeration treatment: pass the chemical nickel wastewater into the pH adjustment tank, add Ca(OH)2, adjust the pH to 11-12, and then perform aeration treatment with an aeration volume of 10-15m 3 / m 2 h, aeration time 90-120min; Fenton treatment: The chemical nickel wastewater after aeration treatment is passed into the pH adjustment tank to adjust the pH and undergo primary Fenton treatment, followed by coagulation and sedimentation treatment, and finally secondary Fenton treatment.

[0006] By adopting the above technical solution, the pH of chemical nickel wastewater is first adjusted to 11-12 during aeration treatment, and a large amount of OH in a strong alkaline environment - It will compete with the complex for nickel ions, breaking the complex balance, causing the complex to dissociate and release free Ni2 + , free Ni 2+ In a high pH environment, it reacts with OH - Combined with the formation of insoluble nickel hydroxide precipitation, it is more conducive to the removal of nickel and improves the removal efficiency. Aeration treatment is more conducive to destroying the complex balance. The water flow disturbance and bubble collision generated by aeration can enhance the interaction between wastewater and OH. - contact, promoting the complexing agent and OH - The competitive reaction accelerates the dissociation of the complex, making more free nickel ions Ni 2+ Release and OH - Combined with the formation of nickel hydroxide precipitation, the stirring effect of aeration treatment can cause small particles of nickel hydroxide precipitation to collide and adsorb, forming larger flocs, which is more conducive to the removal of nickel and improves the removal efficiency. The aeration volume during aeration treatment is controlled at 10-15m 3 / m 2 h. On the one hand, it can avoid violent water disturbances that will break up the formed nickel hydroxide flocs, making it difficult for the particles to aggregate; on the other hand, it can prevent insufficient aeration and uneven mixing of wastewater, thereby reducing the residual complexed nickel.

[0007] The chemical nickel wastewater after aeration treatment is subjected to Fenton treatment, first adjusting the pH to acidic conditions to increase OH - The activity is conducive to the primary Fenton treatment. The primary Fenton treatment oxidizes and destroys the molecular structure of the complex, freeing the nickel ions, and then performs coagulation and sedimentation treatment to separate the nickel ions and oxidation products. Finally, the secondary Fenton treatment is carried out for deep purification to further oxidize the residual complex and organic matter, ensuring that the nickel concentration is reduced to the emission standard, thereby improving the treatment efficiency and effect of chemical nickel wastewater treatment.

[0008] As a preferred embodiment: in the Fenton treatment step, after the chemical nickel wastewater is passed into the pH adjustment tank, 5% dilute sulfuric acid is added to adjust the pH value to 3-5.

[0009] By adopting the above technical solution, after the chemical nickel wastewater in the Fenton treatment is passed into the pH adjustment tank, 5% dilute sulfuric acid is added to adjust the pH value to 3-5, which can ensure the high efficiency of the Fenton reaction, the highest free radical activity, and can effectively oxidize and break the complex, further improving the treatment efficiency and effect of chemical nickel wastewater treatment.

[0010] Preferably, during the primary Fenton treatment, ferrous sulfate is first added to the chemical nickel wastewater, and H2O2 is added after it is completely dissolved, and stirred at a speed of 50-100 rpm for 90-120 minutes; the concentrations of H2O2 and ferrous sulfate are 30% and 10% respectively.

[0011] By adopting the above technical solution, ferrous sulfate provides Fe 2+It reacts with H2O2 to produce Fenton reaction, effectively oxidizing and destroying the complex bonds in chemical nickel wastewater, dissociating the complex nickel into free Ni 2+ , improve the removal efficiency. The speed is too low H2O2 and Fe 2+ It cannot diffuse evenly in the wastewater, easily forming localized high-concentration areas and reducing overall oxidation efficiency. Excessively high rotation speeds can cause a large amount of air to be drawn into the wastewater, where the oxygen may compete with OH, consuming some free radicals. Controlling the rotation speed at 50-100 rpm ensures that H2O2 and ferrous sulfate fully contact the chemical nickel wastewater while reducing ineffective energy consumption and free radical loss.

[0012] In addition, ferrous sulfate is added first to make Fe 2+ Evenly disperse, then add H2O2 to avoid local excess of H2O2 causing Fe 2+ Quickly depleted.

[0013] Preferably, the mass ratio of H2O2 to ferrous sulfate is 1:2.

[0014] By adopting the above technical solution, the excess ferrous sulfate will cause OH to be replaced by the excess Fe 2+ Consumption will reduce the oxidation efficiency, while excess H2O2 will slowly decompose under acidic conditions, resulting in a waste of reagents.

[0015] Preferably, during the primary Fenton treatment, activated carbon fiber and nano-titanium dioxide are added after H2O2 is added; the amount of activated carbon fiber added is 1-3 g / L; and the mass ratio of nano-titanium dioxide to activated carbon fiber is 1:(10-20).

[0016] By adopting the above technical solution, during the first-stage Fenton treatment, activated carbon fiber and nano-titanium dioxide are added after H2O2 is added. The activated carbon fiber acts as an adsorbent to assist in removing unoxidized complexing agents and small molecular organic pollutants. At the same time, its porous structure can adsorb Fe 2+ / Fe 3+ , forming local high-concentration catalytic sites, accelerating the decomposition of H2O2 and improving the removal efficiency of nickel ions. Adding nano-titanium dioxide and loading it on the surface of activated carbon fibers can utilize its photocatalytic properties to generate photogenerated electrons and holes under light conditions, promoting the decomposition of H2O2 to produce hydroxyl free radicals. At the same time, it has a certain adsorption and oxidation effect on organic matter, further improving the treatment effect and efficiency of chemical nickel wastewater.

[0017] As a preferred method, the coagulation and sedimentation treatment is as follows: adding Ca(OH)2 to adjust the pH value to 10.5-11, adding coagulant PAC and flocculant PAM, stirring at a speed of 50-100 rpm for 30 minutes, and then passing through a surface load of 0.6-0.8m 3 / m2 h inclined tube sedimentation tank for secondary Fenton treatment.

[0018] By adopting the above technical solution, coagulation and sedimentation treatment is the key step of primary Fenton treatment and secondary Fenton treatment. Coagulation and sedimentation treatment makes the residual free Ni 2+ Under high pH conditions, nickel hydroxide precipitates are formed and adsorbs residual Fe(OH)3 colloids in the water, reducing the pollutant load of subsequent secondary Fenton and improving the final treatment efficiency.

[0019] Adding coagulant PAC, it dissociates into Al under alkaline conditions 3+ Hydrolysis generates Al(OH)3 colloids, which, together with the Fe(OH)3 colloids produced by the Fenton reaction, act as both "charge neutralizers" and "adsorbent bridges," neutralizing the negative charge on the surface of the colloidal particles in the wastewater and destabilizing them. Through adsorption, PAC / Fe(OH)3 bonds form tiny flocs. The long-chain molecules of the flocculant PAM adsorb these tiny flocs through van der Waals forces, entangled and aggregated them into larger, denser flocs, accelerating sedimentation. The coagulant PAC first forms small flocs through coagulation, while PAM aggregates them through flocculation. The combination of these two significantly improves solid-liquid separation efficiency, reduces effluent turbidity and residual pollutants, and enhances treatment effectiveness.

[0020] Preferably, in the secondary Fenton treatment, coagulant PAC and flocculant PAM are added and stirred at a speed of 50-100 rpm for 30 minutes.

[0021] By adopting the above technical solution, after the first-level Fenton treatment and coagulation sedimentation treatment, the chemical nickel wastewater may still contain incompletely oxidized small molecular organic matter and free Ni released after the network is broken. 2+ , further secondary Fenton treatment is carried out to prevent raw water quality fluctuations in the primary Fenton unit, ensure that indicators such as nickel ions and COD in the wastewater are further reduced, and provide guarantees for the final effluent to meet the standards.

[0022] Preferably, the dosage of the coagulant PAC and the flocculant PAM in the secondary Fenton treatment is 40% of that in the primary Fenton treatment.

[0023] By adopting the above technical solution, the dosage of coagulant PAC and flocculant PAM in the secondary Fenton treatment is 40% of that in the primary Fenton treatment, which not only ensures the secondary Fenton treatment effect but also optimizes the cost of reagents. In addition, excessive coagulant PAC may cause residual Al in the effluent. 3+ Exceeding the standard, or the inclined tube sedimentation tank being clogged due to overly dense flocs, excessive flocculant PAM may cause sticky substances to form in the effluent, affecting subsequent filtration.

[0024] In summary, this application includes at least one of the following beneficial technical effects: (1) This application adjusts the process for treating chemical nickel wastewater and the dosage of each additive to reduce the nickel, phosphorus and COD contents in the wastewater to a minimum of only 0.050 mg / L, 0.183 mg / L and 20.83 mg / L, respectively. The nickel, phosphorus and COD removal rates are as high as 99.92%, 99.79% and 99.52%, respectively, thereby improving the removal effect of chemical nickel wastewater.

[0025] (2) When the present application uses the first-level Fenton treatment, activated carbon fiber and nano-titanium dioxide are added after H2O2 is added, and the ratio of the two is controlled so that the nickel, phosphorus and COD contents in the wastewater are as low as 0.030-0.038 mg / L, 0.155-0.163 mg / L and 12.51-16.65 mg / L, respectively. The nickel, phosphorus and COD removal rates are as high as 99.94-99.95%, 99.81-99.82% and 99.62-99.71%, respectively, thereby improving the removal effect of chemical nickel wastewater.

[0026] (3) By controlling the dosage of coagulant PAC and flocculant PAM in the secondary Fenton treatment, the present application found that when the dosage of coagulant PAC and flocculant PAM was 40% of that in the primary Fenton treatment, the nickel, phosphorus and COD contents in the wastewater and the nickel, phosphorus and COD removal rates were similar and had no significant difference, which could both ensure the treatment effect and reduce costs. DETAILED DESCRIPTION

[0027] The present application is further described in detail below with reference to specific embodiments.

[0028] The following raw materials in this application are all commercially available products. These are provided for the purpose of ensuring full disclosure of the raw materials in this application and should not be construed as limiting their sources. Specifically, they include: ferrous sulfate, 90% active ingredient content, 100-mesh particle size; H₂O₂; activated carbon fiber, 8% moisture, purchased from Shijiazhuang Senhui Environmental Protection Technology Co., Ltd.; nano-titanium dioxide, 20 nm particle size; coagulant PAC, 28% active ingredient content; and flocculant PAM, 88% active ingredient content.

[0029] Example 1 The treatment method of chemical nickel wastewater in Example 1, wherein the chemical nickel wastewater is derived from washing wastewater in the chemical nickel plating process, is specifically as follows: Aeration treatment: The chemical nickel wastewater is passed into the pH adjustment tank, Ca(OH)2 is added, and the pH is adjusted to 11, and then aeration treatment is carried out. The aeration volume is 13m 3 / m 2 h, aeration time 115 min; Fenton treatment: the chemical nickel wastewater after aeration treatment is passed into the pH regulating tank, 5% dilute sulfuric acid is added to adjust the pH value to 2, and the first-level Fenton treatment is carried out (50 mL / L of 30% concentration of ferrous sulfate and 50 mL / L of 10% concentration of H2O2 are added, and stirred at a speed of 80 rpm for 115 min), followed by coagulation and sedimentation treatment (Ca(OH)2 is added to adjust the pH value to 10.5, 200 mg / L coagulant PAC and 5 mg / L flocculant PAM are added, and stirred at a speed of 80 rpm for 30 min, and the surface load is 0.7 m 3 / m 2 h inclined tube sedimentation tank), and finally a secondary Fenton treatment (adding 200 mg / L coagulant PAC and 5 mg / L flocculant PAM, stirring at 50-100 rpm for 30 min).

[0030] Example 2 The treatment method of chemical nickel wastewater in Example 2 differs from that in Example 1 in that, during Fenton treatment, after the chemical nickel wastewater is passed into the pH adjustment tank, 5% dilute sulfuric acid is added to adjust the pH value to 4. The remaining steps are the same as in Example 1.

[0031] Example 3 The treatment method of chemical nickel wastewater in Example 3 differs from that in Example 2 in that, during the primary Fenton treatment, 50 mL / L of 30% concentration of ferrous sulfate is first added, and after complete dissolution, 50 mL / L of 10% concentration of H2O2 is added, and the mixture is stirred at a speed of 80 rpm for 115 min. The concentrations of H2O2 and ferrous sulfate are 30% and 10%, respectively. The remaining steps are the same as in Example 2.

[0032] Example 4 The treatment method of chemical nickel wastewater in Example 4 differs from that in Example 3 in that the addition amounts of H2O2 and ferrous sulfate are 25 mL / L and 50 mL / L, respectively, and the remaining steps are the same as those in Example 3.

[0033] Example 5 The treatment method of chemical nickel wastewater in Example 5 differs from that in Example 4 in that, during the primary Fenton treatment, activated carbon fiber and nano-titanium dioxide are added after H2O2 is added; the addition amount of activated carbon fiber is 2 g / L; the addition amount of nano-titanium dioxide is 0.25 g / L, and the remaining steps are the same as in Example 4.

[0034] Examples 6-9 The treatment method of chemical nickel wastewater in Examples 6-9 differs from that in Example 5 in that the addition amounts of nano-titanium dioxide and activated carbon fiber are 2 g / L and 0.2 g / L, 2 g / L and 0.13 g / L, 2 g / L and 0.1 g / L, and 2 g / L and 0.08 g / L, respectively, and the remaining steps are the same as in Example 4.

[0035] Example 10 The treatment method of chemical nickel wastewater in Example 10 is different from that in Example 7 in that the coagulation and sedimentation treatment is as follows: Ca(OH)2 is added to adjust the pH value to 10.5, 250 mg / L of coagulant PAC and 5 mg / L of flocculant PAM are added, the mixture is stirred at a speed of 80 rpm for 30 min, and the surface load is 0.7 m 3 / m 2 h inclined tube sedimentation tank, the effluent enters the secondary Fenton treatment, and the remaining steps are the same as Example 7.

[0036] Example 11 The treatment method of chemical nickel wastewater in Example 11 differs from that in Example 10 in that 100 mg / L of coagulant PAC and 2 mg / L of flocculant PAM are added in the secondary Fenton treatment, and the remaining steps are the same as those in Example 10.

[0037] Comparative Example 1 The treatment method of chemical nickel wastewater in Comparative Example 1 is different from that in Example 1 in that aeration treatment is not performed in the treatment of chemical nickel wastewater, and the remaining steps are the same as those in Example 1.

[0038] Comparative Example 2 The treatment method of chemical nickel wastewater in Comparative Example 1 is different from that in Example 1 in that the chemical nickel wastewater treatment is not subjected to secondary Fenton treatment, and the remaining steps are the same as those in Example 1.

[0039] Performance test (I) The following method was used to detect the chemical nickel wastewater, the wastewater obtained by the treatment methods of chemical nickel wastewater in Examples 1-11 and Comparative Examples 1-2. The specific test results are shown in Table 1.

[0040] The nickel, phosphorus and COD contents of the untreated chemical nickel wastewater and the chemical nickel wastewater treated in Examples 1-11 and Comparative Examples 1-2 were measured, and the nickel, phosphorus and COD removal rates were calculated based on the measurement results.

[0041] Table 1 Test results of different chemical nickel wastewater treatment methods The treatment test results in Table 1 show that after treatment with the chemical nickel wastewater treatment method of the present application, the nickel, phosphorus and COD contents in the wastewater are as low as 0.035 mg / L, 0.159 mg / L and 9.31 mg / L, and the nickel, phosphorus and COD removal rates are as high as 99.97%, 99.85% and 99.79%, respectively, which improves the removal effect of chemical nickel wastewater treatment.

[0042] According to the treatment test data of the chemical nickel wastewater in Examples 1 and 2, it was found that after treatment by the treatment method of the chemical nickel wastewater in Example 2, the nickel, phosphorus and COD contents in the wastewater were only 0.061 mg / L, 0.208 mg / L and 25.98 mg / L, respectively, and the nickel, phosphorus and COD removal rates were as high as 99.90%, 99.76% and 99.41%, respectively, which were all higher than those in Example 1. This indicates that during Fenton treatment, after the chemical nickel wastewater is passed into the pH adjustment tank, 5% dilute sulfuric acid is added to adjust the pH value to 4, which can improve the removal effect of the chemical nickel wastewater.

[0043] According to the treatment test data of the chemical nickel wastewater in Examples 2 and 3, it was found that after treatment by the treatment method of the chemical nickel wastewater in Example 3, the nickel, phosphorus and COD contents in the wastewater were only 0.053 mg / L, 0.199 mg / L and 22.98 mg / L, and the nickel, phosphorus and COD removal rates were as high as 99.91%, 99.77% and 99.48%, respectively, which were all higher than those in Example 2, indicating that ferrous sulfate was first added to the chemical nickel wastewater, and H2O2 was added after it was completely dissolved, and the mass ratio of H2O2 to ferrous sulfate was 1:2, which was more appropriate, and the removal effect of the chemical nickel wastewater treatment could be further improved.

[0044] According to the treatment test data of the chemical nickel wastewater in Examples 3 and 4, it was found that after treatment by the treatment method of chemical nickel wastewater in Example 4, the lowest nickel, phosphorus and COD contents in the wastewater were only 0.050 mg / L, 0.183 mg / L and 20.83 mg / L, and the nickel, phosphorus and COD removal rates were as high as 99.92%, 99.79% and 99.52%, respectively, which were all higher than those in Example 3. This shows that during the primary Fenton treatment, the addition of activated carbon fiber and nano-titanium dioxide after the addition of H2O2 can further improve the removal effect of the chemical nickel wastewater.

[0045] According to the treatment test data of the chemical nickel wastewater of Examples 5-9, it was found that after treatment by the treatment method of the chemical nickel wastewater of Examples 6-8, the nickel, phosphorus and COD contents in the wastewater were only 0.030-0.038 mg / L, 0.155-0.163 mg / L and 12.51-16.65 mg / L, respectively, and the nickel, phosphorus and COD removal rates were as high as 99.94-99.95%, 99.81-99.82% and 99.62-99.71%, respectively, which were all higher than those in Example 5 and Example 9, indicating that during the primary Fenton treatment, after adding H2O2, activated carbon fiber and nano-titanium dioxide were continued to be added, and the mass ratio of nano-titanium dioxide to activated carbon fiber was 1:(10-20), which was more appropriate, and could further improve the removal effect of the chemical nickel wastewater.

[0046] According to the treatment test data of the chemical nickel wastewater in Examples 7 and 10, it was found that after treatment by the treatment method of the chemical nickel wastewater in Examples 6-8, the lowest nickel, phosphorus and COD contents in the wastewater were only 0.021 mg / L, 0.132 mg / L and 9.40 mg / L, and the nickel, phosphorus and COD removal rates were as high as 99.97%, 99.85% and 99.79%, respectively, which were all higher than those in Example 7, indicating that the dosage of the coagulant PAC and the flocculant PAM in Example 10 was more appropriate, which can further improve the removal effect of the chemical nickel wastewater.

[0047] According to the treatment test data of the chemical nickel wastewater in Examples 10 and 11, it was found that after treatment by the treatment method of the chemical nickel wastewater in Example 11, the nickel, phosphorus and COD contents in the wastewater and the nickel, phosphorus and COD removal rates were similar to those in Example 10, indicating that the treatment effect can be guaranteed when the dosage of coagulant PAC and flocculant PAM in the secondary Fenton treatment is 40% of that in the primary Fenton treatment.

[0048] According to the treatment test data of the chemical nickel wastewater in Example 1 and Comparative Examples 1-2, it was found that the aeration treatment and the secondary Fenton treatment can improve the removal effect of the chemical nickel wastewater to varying degrees.

[0049] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A method for treating chemical nickel wastewater, characterized in that: The chemical nickel wastewater is derived from washing wastewater in the chemical nickel plating process. The treatment method of the chemical nickel wastewater comprises the following steps: Aeration treatment: pass the chemical nickel wastewater into the pH adjustment tank, add Ca(OH)2, adjust the pH to 11-12, and then perform aeration treatment with an aeration volume of 10-15m 3 / m 2 h, aeration time 90-120min; Fenton treatment: The chemical nickel wastewater after aeration treatment is passed into the pH adjustment tank to adjust the pH and undergo primary Fenton treatment, followed by coagulation and sedimentation treatment, and finally secondary Fenton treatment.

2. The method for treating chemical nickel wastewater according to claim 1, wherein: In the Fenton treatment step, the chemical nickel wastewater is passed into the pH adjustment tank, and then 5% dilute sulfuric acid is added to adjust the pH value to 3-5.

3. The method for treating chemical nickel wastewater according to claim 1, wherein: During the primary Fenton treatment, ferrous sulfate is first added to the chemical nickel wastewater, and H2O2 is added after it is completely dissolved, followed by stirring at a speed of 50-100 rpm for 90-120 minutes; the concentrations of H2O2 and ferrous sulfate are 30% and 10%, respectively.

4. The method for treating chemical nickel wastewater according to claim 3, wherein: The mass ratio of H2O2 to ferrous sulfate is 1:

2.

5. The method for treating chemical nickel wastewater according to claim 3, wherein: During the primary Fenton treatment, activated carbon fiber and nano-titanium dioxide are added after H2O2 is added; the amount of activated carbon fiber added is 1-3 g / L; and the mass ratio of nano-titanium dioxide to activated carbon fiber is 1:(10-20).

6. The method for treating chemical nickel wastewater according to claim 1, wherein: The coagulation and sedimentation treatment is specifically as follows: adding Ca(OH)2 to adjust the pH value to 10.5-11, adding coagulant PAC and flocculant PAM, stirring at a speed of 50-100 rpm for 30 minutes, and then passing through a surface load of 0.6-0.8m 3 / m 2 h inclined tube sedimentation tank for secondary Fenton treatment.

7. The method for treating chemical nickel wastewater according to claim 1, wherein: In the secondary Fenton treatment, coagulant PAC and flocculant PAM were added and stirred at a speed of 50-100 rpm for 30 minutes.

8. The method for treating chemical nickel wastewater according to claim 7, wherein: The dosage of the coagulant PAC and the flocculant PAM in the secondary Fenton treatment is 40% of that in the primary Fenton treatment.

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