Method for recycling nickel and iron metals in electroplating solid waste acid leachate to prepare cathode and remove nitrate nitrogen

Abstract

The invention discloses a method for removing nitrate nitrogen by recycling nickel and iron metals in an electroplating solid waste acid leaching solution to prepare a cathode. The nitrate nitrogen removal effect is achieved under different conditions through regulation and control of parameters in an acid leaching solution electrodeposition process. According to the electrode, nickel and iron heavy metals contained in electroplating wastewater metal solid waste acid immersion liquid serve as basic materials, loose and porous foamy copper CF with the large specific surface area serves as a substrate, the nickel and iron heavy metals grow on the surface of the foamy copper in situ in the form of LDH through an electrodeposition method, and the NiFe-LDH / CF electrode material is obtained. Meanwhile, the electrode is found to have an excellent electrochemical nitrate nitrogen removal effect by regulating and controlling the initial state of an acid leaching solution in the electro-deposition process. According to the prepared electrode material, heavy metal in electroplating wastewater serves as a source, electrodeposition is adopted, other chemical components do not need to be added, and electrodeposition wastewater is reused after being simply treated; when the electrode is used for treating nitrate nitrogen in electroplating wastewater, the purpose of treating waste with waste is achieved.

Description

Technical Field

[0001] The invention relates to a method for preparing a cathode for removing nitrate nitrogen by recycling nickel and iron metals from electroplating solid waste acid leaching solution, specifically a method for preparing electrode materials using heavy metals (nickel and iron) recovered from electroplating wastewater as effective components and applying the method to degrade nitrate nitrogen in electroplating wastewater, belonging to the technical field of wastewater treatment. Background Art

[0002] At present, the utilization and recovery of heavy metals in electroplating wastewater is mainly to prepare them into building materials or generate precipitation. Existing research has found a method for selectively separating chromium ions and a method for combining pyrometallurgy and hydrometallurgy to recover heavy metals copper and zinc in electroplating sludge. However, there is no economical and effective method to extract and separate the relatively large content of nickel and iron heavy metals in electroplating wastewater.

[0003] Heavy metal ions are common pollutants in electroplating wastewater, such as high concentrations of iron, chromium, copper, nickel, etc. If a large amount of heavy metal ions are directly discharged into the water, it will cause great harm to human health. Therefore, how to effectively treat heavy metal ions in electroplating wastewater is particularly important. Existing technology can already separate heavy metals from electroplating wastewater, but the metal solid waste generated after treatment still contains a large amount of heavy metals, which will not only cause a waste of valuable metal resources in the metal solid waste, but also pollute the environment and endanger human health.

[0004] The resource recovery treatment of heavy metals in electroplating wastewater has always attracted much attention and is an urgent problem to be solved in the electroplating industry and environmental engineering field. At present, the resource recovery of metal solid waste in electroplating wastewater can be divided into two categories: overall resource recovery and heavy metal resource recovery. Overall resource recovery refers to the process of using metal solid waste as a production raw material to partially replace other raw materials in the production of building materials. It has been reported that metal solid waste can be used in the production of clay bricks and expanded clay. However, preparing metal solid waste into building materials will cause a large amount of valuable metal resources to be wasted, and from a development perspective, heavy metals in building materials will inevitably leach from the building materials over time, thereby contaminating the surrounding soil or spreading with groundwater, polluting a larger area.

[0005] The resource recovery of heavy metals contained in the metal solid waste of electroplating wastewater is mainly through pyrometallurgy, hydrometallurgy, ion exchange resin interception, microbial leaching and other methods. Pyrometallurgy converts specific metals into volatile chloride salts or insoluble sulfides by adding sulfides or chlorides and then heat treating at a high temperature to achieve heavy metal resource recovery. This method has a high reaction cost and can only be used for a few specific metals. It cannot be widely used in electroplating sludges with a variety of compositions or for the recovery of all valuable metal components in the same sludge. Hydrometallurgy mainly refers to first using acid to fully dissolve the electroplating sludge so that the heavy metals contained therein are released indiscriminately into the leaching solution, and then using chemical precipitation / solvent extraction / electrodeposition to recover the heavy metals. This method has the disadvantages of slow precipitation of heavy metals, no selectivity, and large amount of strong acid / strong base. The ion resin interception method is to effectively enrich and recover a variety of heavy metal ions by using resins. This method has the disadvantages of high material cost and low adsorption capacity. Microbial leaching has been widely studied in recent years as an effective, green and environmentally friendly method for recovering precious metals from metal solid waste. However, this method is usually slow in recovery and is not applicable when the concentration of heavy metals in the sludge is very high. In existing studies, experiments have shown that chromium ions can be selectively separated from the acid leaching solution by phosphate, and heavy metals copper and zinc can be recovered from electroplating sludge by sulfate roasting. However, there is no economical and effective method to extract and separate heavy metals such as nickel and iron that are relatively high in the acid leaching solution.

[0006] The several existing technologies for resource recovery of heavy metals in metal solid waste from electroplating wastewater cannot directly utilize or recover the nickel and iron heavy metal components in the acid leaching solution of the metal solid waste economically and effectively. Summary of the invention

[0007] The purpose of the present invention is to solve the problem that heavy metals in the acid leaching solution of electroplating wastewater metal solid waste are difficult to recover, resulting in a large amount of heavy metal waste or environmental pollution. A method for resource utilization of heavy metals in the acid leaching solution and preparing them into electrodes that can degrade nitrate nitrogen is proposed. It mainly utilizes heavy metals in electroplating wastewater metal solid waste as effective components, loads them on the surface of loose and porous carrier raw materials to make electrode materials, and uses the electrode as a cathode to degrade nitrate nitrogen in electroplating wastewater, so as to achieve the purpose of "waste treatment with waste".

[0008] A method for recovering nickel and iron metals from electroplating solid waste acid leaching solution to prepare a cathode for removing nitrate nitrogen. Metal solid waste containing a large amount of nickel and iron is subjected to an acid leaching method so that most of the metal substances therein are dissolved in an ionic or complex ionic state, and then the pH of the acid leaching solution is adjusted to neutral. Using foamed copper as a carrier, the foamed copper is immersed in the acid leaching solution after the pH is adjusted, and is prepared into a NiFe-LDH / CF electrode with a layered double hydroxide containing nickel and iron on the surface by an electrodeposition method. The NiFe-LDH / CF electrode is used as a cathode to effectively degrade nitrates, so as to achieve the purpose of "treating waste with waste".

[0009] The electrode material of the present invention has the following benefits:

[0010] (1) The present invention uses heavy metals in electroplating wastewater as effective components of electrode materials, and makes resource utilization of heavy metals, thereby solving the problems of waste of valuable metal resources and possible re-release of heavy metals to cause secondary pollution caused by treating solid metal waste in electroplating wastewater in the preparation of building materials, as well as the difficulty in separating single metal components when recovering heavy metals. Secondly, since there are many heavy metal components in electroplating wastewater, it is inevitable to add other substances to recover a single heavy metal from electroplating wastewater to produce new pollutants. However, when multiple heavy metals in electroplating wastewater are used as a whole for the preparation of electrode materials, the synergistic effect between different heavy metals will improve the performance of electrode materials. At the same time, using heavy metals in electroplating wastewater to prepare electrode materials is an economical and reasonable method for recovering heavy metals, which also solves the problem of heavy metal waste.

[0011] (2) The present invention uses a simple electrodeposition technology to prepare electrodes. Compared with other methods, no other chemical substances need to be added, which reduces the preparation cost of electrode materials and the secondary pollution that may be caused. At the same time, without adding other chemical substances, the components in the acid leaching wastewater are relatively stable, and the heavy metal components that are not attached to the electrode surface can be reused after simple treatment, which reduces the cost of treating electrodeposition wastewater and avoids the waste of heavy metal resources.

[0012] (3) The NiFe-LDH / CF electrode prepared by the present invention using heavy metals in electroplating wastewater as active ingredients is an electrode material with high efficiency, good stability and high selectivity, which can effectively degrade nitrate nitrogen in electroplating wastewater. This makes the heavy metal pollutants in electroplating wastewater have the potential to repair water bodies containing nitrate nitrogen pollutants, thus achieving the purpose of "treating waste with waste". BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 The SEM image and mapping image of the NiFe-LDH / CF electrode with the best performance.

[0014] Figure 2This is a comparison chart of the nitrate removal efficiency of electrodes prepared under different pH conditions during the electrodeposition process.

[0015] Figure 3 This is a comparison chart of the nitrate removal efficiency of electrodes prepared at different electrodeposition times during the electrodeposition process under optimal pH conditions.

[0016] Figure 4 This is a comparison chart of the nitrate removal efficiency of the optimal electrode at different initial nitrate nitrogen concentrations during the nitrate electroreduction process. DETAILED DESCRIPTION

[0017] The following is a further description of the present invention, rather than a limitation of the present invention.

[0018] The specific preparation process of NiFe-LDH / CF electrode includes the following steps:

[0019] Step 1: Cut the 3×2cm 2 The foam copper was placed in a beaker and immersed in an acetone solution for 15-20 minutes to remove organic matter on its surface. After being taken out, it was rinsed with deionized water.

[0020] Step 2: Soak the copper foam in anhydrous ethanol and ultrasonically remove the oxide on its surface for 15-20 minutes. After taking it out, rinse it with deionized water.

[0021] Step 3: Ultrasonicate the copper foam with deionized water for 15-20 minutes, and place the treated nickel foam in anhydrous ethanol for later use.

[0022] Step 4: Take 50-70 mL of the acid extract in a 100 mL reactor, and adjust the pH of the acid extract to 6-8 using 3M sodium hydroxide solution while stirring at a speed of 500-600 rpm.

[0023] Step 5: Use a two-electrode system, with a titanium ruthenium iridium electrode as the anode and the cleaned copper foam as the cathode. The distance between the anode and cathode is 1.5 cm, and the anode and cathode are inserted into the acid leaching wastewater.

[0024] Step 6: At a current density of 10-20 mA / cm 2 Under the same conditions, the power was turned on for 20-30 minutes, after which the foam copper was removed and the electrode surface was rinsed with deionized water.

[0025] Step 7: Place the prepared electrode in a vacuum oven and dry it under vacuum for 6-8 hours. Take it out and cool it to room temperature to obtain the NiFe-LDH / CF electrode.

[0026] Comparison of nitrate removal efficiency of electrodes prepared under different pH conditions during electrodeposition

[0027] Step 1: Take 50 mL of the acid extract in a 100 mL reactor, and use 3 M sodium hydroxide solution to adjust the pH of the acid extract to 3, 5, 7, and 9 respectively under a stirring speed of 500 rpm.

[0028] Step 2: Use a two-electrode system, with a titanium ruthenium iridium electrode as the anode and the cleaned copper foam as the cathode. The distance between the anode and cathode is 1.5 cm, and the anode and cathode are inserted into the acid leaching wastewater.

[0029] Step 3: At a current density of 10 mA / cm 2 Under the conditions, the power was turned on for 20 minutes, then the electrode was taken out and the electrode surface was rinsed with deionized water.

[0030] Step 4: Place the prepared electrode in a vacuum oven and vacuum dry it for 6 hours. Take it out and cool it to room temperature to obtain the electrodes prepared under different pH conditions.

[0031] Step 5: Place 21 mg of sodium nitrate and 497 mg of sodium sulfate in a 100 mL reactor, add 70 mL of deionized water, and stir for 5 min at a stirring speed of 500 rpm to obtain simulated wastewater with a nitrate nitrogen concentration of 50 mg / L.

[0032] Step 6: Use a two-electrode system, with a titanium ruthenium iridium electrode as the anode and the prepared NiFe-LDH / CF electrode as the cathode. The distance between the anode and cathode is 1.5 cm. Insert the anode and cathode into the simulated wastewater prepared in step 5.

[0033] Step 7: Turn on the power supply, adjust the DC current to 60mA, conduct a 3h degradation experiment, and take samples every 30min.

[0034] Step 8: Analyze and measure the sample by UV-Vis spectroscopy to determine the nitrate nitrogen concentration in the sample.

[0035] Comparison of nitrate removal efficiency of electrodes prepared with different electrodeposition times during electrodeposition under optimal pH conditions

[0036] Step 1: Take 50 mL of the acid extract in a 100 mL reactor, and adjust the pH of the acid extract to 7 using 3 M sodium hydroxide solution while stirring at 500 rpm.

[0037] Step 2: Use a two-electrode system, with a titanium ruthenium iridium electrode as the anode and the cleaned copper foam as the cathode. The distance between the anode and cathode is 1.5 cm, and the anode and cathode are inserted into the acid leaching wastewater.

[0038] Step 3: At a current density of 10 mA / cm 2 Under the same conditions, the power was applied for 10, 15, 20, and 25 min, respectively. After that, the electrode was taken out and the electrode surface was rinsed with deionized water.

[0039] Step 4: Place the prepared electrode in a vacuum oven and vacuum dry it for 6 hours. Take it out and cool it to room temperature to obtain the electrodes prepared under different pH conditions.

[0040] Step 5: Place 21 mg of sodium nitrate and 497 mg of sodium sulfate in a 100 mL reactor, add 70 mL of deionized water, and stir for 5 min at a stirring speed of 500 rpm to obtain simulated wastewater with a nitrate nitrogen concentration of 50 mg / L.

[0041] Step 6: Use a two-electrode system, with a titanium ruthenium iridium electrode as the anode and the prepared NiFe-LDH / CF electrode as the cathode. The distance between the anode and cathode is 1.5 cm. Insert the anode and cathode into the simulated wastewater prepared in step 5.

[0042] Step 7: Turn on the power supply, adjust the DC current to 60mA, conduct a 3h degradation experiment, and take samples every 30min.

[0043] Step 8: Analyze and measure the sample by UV-Vis spectroscopy to determine the nitrate nitrogen concentration in the sample.

[0044] Comparison of nitrate removal efficiency of the best electrode at different initial nitrate nitrogen concentrations during nitrate electroreduction

[0045] Step 1: Prepare electrodes under the optimal preparation conditions explored in the above experiments.

[0046] Step 2: Place 11, 21, 42, and 84 mg of sodium nitrate and 497 mg of sodium sulfate in a 100 mL reactor, add 70 mL of deionized water, and stir for 5 min at a stirring speed of 500 rpm to obtain simulated wastewater with nitrate nitrogen concentrations of 25, 50, 100, and 200 mg / L.

[0047] Step 3: Use a two-electrode system, with a titanium ruthenium iridium electrode as the anode and the prepared NiFe-LDH / CF electrode as the cathode. The distance between the anode and cathode is 1.5 cm. Insert the anode and cathode into the simulated wastewater configured in step 5.

[0048] Step 4: Turn on the power supply, adjust the DC current to 60mA, conduct a degradation experiment for 3 hours, and take samples every 30 minutes.

[0049] Step 5: Analyze and measure the sample by UV-Vis spectroscopy to determine the nitrate nitrogen concentration in the sample.

[0050] from Figure 1It can be seen from the SEM image that a hierarchical structure of nanoflowers assembled from nanosheets has grown on the electrode surface, indicating that heavy metals such as iron and nickel are attached to the electrode surface in the form of layered hydroxides. Figure 1 It can be seen from the mapping diagram that heavy metals such as iron and nickel are successfully grown in situ on the electrode surface and are evenly distributed on the foam copper substrate.

[0051] from Figure 2 It can be seen that the electrode prepared under neutral pH conditions has a better effect on the removal of nitrate nitrogen. This may be because the neutral environment is more conducive to the formation of NiFe-LDH, which makes the electrode surface have more active sites. However, the NiFe-LDH formed on the electrode surface in an acidic environment is difficult to form or difficult to maintain after formation, and Ni(OH)2 and Fe(OH)3 are more easily generated in an alkaline environment, which reduces the available ionic Ni and Fe in the acid leaching wastewater.

[0052] from Figure 3 It can be seen that as the electrodeposition time gradually increases, the removal efficiency of the prepared electrode for nitrate nitrogen increases. When the electrodeposition time exceeds 20 minutes, as the electrodeposition time gradually increases, the removal efficiency of the electrode for nitrate nitrogen does not change significantly. This may be because when the electrodeposition time is short, there are fewer active substances on the electrode surface, thereby reducing the overall removal rate. As the electrodeposition time gradually increases, the catalytically active substances on the electrode surface gradually increase, but the active substances deposited later are not firmly bonded to the substrate, so some active substances will detach in subsequent treatments, so the nitrate nitrogen removal effect of the electrode is not greatly affected.

[0053] from Figure 4 It can be seen that the electrode can degrade nitrate nitrogen more efficiently when the nitrate nitrogen concentration is lower than 50 mg / L. When the nitrate nitrogen concentration is 25 mg / L, the electrode can remove 90% of the nitrate nitrogen after 120 minutes of reaction. - -N increased to 200mg / LNO3 - -N, the degradation rate decreased from 90% to 45%. Although the degradation rate of nitrate nitrogen by the electrode decreased, the total amount of nitrate nitrogen treated increased. This also shows that the electrode is more suitable for the removal of low concentration nitrate nitrogen.

Claims

1. A method for recovering nickel and iron metals from electroplating solid waste acid leaching solution and preparing cathode to remove nitrate nitrogen, characterized in that: The metal solid waste containing nickel and iron is subjected to an acid leaching method so that most of the metal substances therein are dissolved in ionic or complex ionic states, and then the pH of the acid leaching solution is adjusted to neutral; using foam copper as a carrier, the foam copper is immersed in the acid leaching solution with adjusted pH, and is prepared into a NiFe-LDH / CF electrode with a layered double hydroxide containing nickel and iron on the surface by an electrodeposition method; and the NiFe-LDH / CF electrode is used as a cathode to degrade nitrate.

2. The method for recovering nickel and iron metals from electroplating solid waste acid leaching solution and preparing cathode for removing nitrate nitrogen according to claim 1, characterized in that: The preparation process of NiFe-LDH / CF electrode is as follows: The following steps are involved: Step 1: Place the cut copper foam into a beaker, immerse it in acetone solution and perform ultrasonic treatment to remove organic matter on its surface, then take it out and rinse it with deionized water; Step 2: Soak the copper foam in anhydrous ethanol and perform ultrasound to remove the oxide on its surface, then take it out and rinse it with deionized water; Step 3: Ultrasonicate the copper foam with deionized water, and place the treated nickel foam in anhydrous ethanol for later use; Step 4: Put the acid leaching solution into a reactor, and adjust the pH of the acid leaching solution to 6-8 using 3M sodium hydroxide solution under stirring; Step 5: Use a two-electrode system, with a titanium ruthenium iridium electrode as the anode and a cleaned copper foam as the cathode. The distance between the cathode and cathode is 1.5 cm, and the cathode and cathode are inserted into the acid leaching wastewater; Step 6: At a current density of 10-20 mA / cm 2 Under the conditions, power on for 20-30 minutes, then take out the foam copper and rinse the electrode surface with deionized water; Step 7: The prepared electrode is vacuum dried, taken out and cooled to room temperature to obtain a NiFe-LDH / CF electrode.

3. The method for recovering nickel and iron metals from electroplating solid waste acid leaching solution and preparing cathode for removing nitrate nitrogen according to claim 1, characterized in that: The size of the cut copper foam is 3×2cm 2 .

4. The method for recovering nickel and iron metals from electroplating solid waste acid leaching solution and preparing cathode for removing nitrate nitrogen according to claim 1, characterized in that: The ultrasonic time in the first step, the second step and the third step is 15-20 minutes.

5. The method for recovering nickel and iron metals from electroplating solid waste acid leaching solution and preparing cathode for removing nitrate nitrogen according to claim 1, characterized in that: In the fourth step, the stirring speed is 500-600 rpm.

6. The method for recovering nickel and iron metals from electroplating solid waste acid leaching solution and preparing cathode for removing nitrate nitrogen according to claim 1, characterized in that: In step 7, vacuum dry in a vacuum drying oven for 6-8 hours.

7. The method for recovering nickel and iron metals from electroplating solid waste acid leaching solution and preparing cathode for removing nitrate nitrogen according to claim 1, characterized in that: The nitrate concentration is 50 mg / L.

8. The method for recovering nickel and iron metals from electroplating solid waste acid leaching solution and preparing cathode for removing nitrate nitrogen according to claim 7, characterized in that Nitrate is nitrate nitrogen.

9. A NiFe-LDH / CF electrode, characterized in that: The electrode is prepared through a specific process, including the following steps: Step 1: Cut the 3×2cm 2 The foam copper was placed in a beaker and immersed in an acetone solution for 15-20 minutes to remove organic matter on its surface. After being taken out, it was rinsed with deionized water. Step 2: Soak the copper foam in anhydrous ethanol and ultrasonically treat for 15-20 minutes to remove the oxide on its surface, then rinse it with deionized water; Step 3: Ultrasonicate the copper foam with deionized water for 15-20 minutes, and place the treated nickel foam in anhydrous ethanol for later use; Step 4: Take 50-70 mL of the acid extract in a 100 mL reactor, and adjust the pH of the acid extract to 6-8 using 3M sodium hydroxide solution under a stirring speed of 500-600 rpm; Step 5: Use a two-electrode system, with a titanium ruthenium iridium electrode as the anode and a cleaned copper foam as the cathode. The distance between the cathode and cathode is 1.5 cm, and the cathode and cathode are inserted into the acid leaching wastewater; Step 6: At a current density of 10-20 mA / cm 2 Under the conditions, the power was turned on for 20-30 minutes, after which the foam copper was taken out and the electrode surface was rinsed with deionized water; Step 7: Place the prepared electrode in a vacuum oven and dry it under vacuum for 6-8 hours. Take it out and cool it to room temperature to obtain the NiFe-LDH / CF electrode.

10. The NiFe-LDH / CF electrode according to claim 9, characterized in that: In the fourth step, the pH is 7, and in the sixth step, the power-on time is 20 minutes.

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