Iron and copper removal utilization process for iron-based copper plating wastewater

Abstract

The invention relates to the technical field of industrial wastewater treatment and resource recovery, and discloses an iron and copper removal utilization process for iron-based copper plating wastewater, which comprises the steps of pretreatment and oxidation, ferric sulfate extraction, copper sulfate extraction and sodium sulfate concentration and evaporation extraction. The method comprises the following steps: filtering wastewater, adjusting the pH value to 9.5-10.0, and carrying out aeration oxidation to convert ferrous iron into ferric iron; the method comprises the following steps: carrying out segmented adjustment of pH (iron removal by 4.1-4.3 and copper removal by 8.5-9.0) to realize iron-copper separation, and respectively dissolving filter cakes with concentrated sulfuric acid to prepare a ferric sulfate solution (containing 9-12% of iron) and a copper sulfate solution (containing 5-7.5% of copper); and carrying out membrane concentration and evaporation on the copper-removed clear liquid to obtain anhydrous sodium sulfate. According to the process, the problems of incomplete ferrous precipitation and high hazardous waste treatment cost in a traditional process are solved, iron and copper resource utilization and wastewater zero discharge are realized, the iron and copper separation rate exceeds 99%, and the economic benefit and the process stability are remarkably improved.

Description

Technical Field

[0001] The invention relates to the technical field of industrial wastewater treatment and resource recovery, and in particular to a process for removing iron and copper from iron-based copper plating wastewater. Background Art

[0002] Copper plating of iron materials (such as high-speed welding wire) primarily involves chemically plating the surface of iron-based materials with copper sulfate. The resulting wastewater primarily consists of copper sulfate and ferrous sulfate, along with other impurities such as wire drawing powder and calcium stearate. The currently widely used treatment method involves alkaline precipitation followed by membrane filtration and then MVR evaporation and concentration. This involves directly precipitating iron and copper as hydroxides with alkali. The filtrate is then subjected to deep treatment through sand filtration, carbon filtration, PP cotton filtration, ultrafiltration, and RO membrane filtration before being concentrated and evaporated to form solid sodium sulfate. The filter cake is then handed over to a third-party for solid waste disposal. Because the ferrous ion precipitation pH is > 10, and the subsequent concentration of the water requires adjustment, many operations often result in incomplete ferrous precipitation due to inadequate pH or insufficient precipitation time, leading to incomplete ferrous precipitation and subsequent process flow. This causes the residual ferrous iron to be gradually oxidized in subsequent processes to form ferric hydroxide precipitates, which can clog subsequent filters such as sand filtration, carbon filtration, PP cotton filtration, ultrafiltration, and RO membranes, severely impacting production. Furthermore, the precipitated waste residue produced by this process is classified as hazardous waste due to its presence of heavy metal copper, making it expensive to entrust a qualified third party with its disposal. Summary of the Invention

[0003] (1) Technical problems solved

[0004] In view of the shortcomings of the existing technology, the present invention provides a process for removing iron and copper from iron-based copper plating wastewater, which solves the problems raised in the above background technology.

[0005] (2) Technical solution

[0006] To achieve the above object, the present invention provides the following technical solution: a process for removing iron and copper from iron-based copper plating wastewater, comprising the following steps:

[0007] Step 1, pretreatment and oxidation: The wastewater is first physically filtered to remove mechanical impurities (such as drawing powder, foam, etc.), and the impurities are cleaned and treated as ordinary industrial waste; the filtrate is stirred with liquid alkali to adjust the pH to 9.5-10.0, and compressed air is introduced for aeration oxidation for about 1 hour, during which the pH is maintained at ≥9.0, so that the black-green ferrous hydroxide precipitate is oxidized to a yellow-brown ferric hydroxide precipitate, ensuring that the divalent iron is completely converted to trivalent iron;

[0008] Step 2, extracting ferric sulfate: adjusting the solution pH to 4.1-4.3 (preferably pH 4.2) with sulfuric acid, stabilizing for more than 15 minutes, and adding PAM for flocculation and precipitation; filtering the bottom slurry through a filter press, washing the filter cake with clean water to remove soluble copper and sodium salts, and returning the filtrate to the original water tank; transferring the filter cake (ferric hydroxide) into a reactor, adding concentrated sulfuric acid according to the iron content to dissolve it, heating to 60-80° C., stirring for 1-2 hours until completely dissolved, and cooling to obtain a ferric sulfate solution containing 9-12% iron, which can be used as a water treatment agent or iron supplement product;

[0009] Step 3, extracting copper sulfate: After iron removal, the filtrate is adjusted to a pH of 8.5-9.0 with sodium hydroxide, stabilized for more than 15 minutes, and then PAM is added for flocculation and precipitation; the bottom slurry is filtered through a filter press, the filter cake is washed with clean water to remove soluble salts, and the filtrate is returned to the process before copper removal; the filter cake (copper hydroxide) is transferred to a reactor, concentrated sulfuric acid is added according to the copper content to dissolve it, and after cooling, a copper sulfate solution containing 5-7.5% copper is obtained, which can be used as a copper plating raw material or for other purposes;

[0010] Step 4: Concentration and evaporation to extract sodium sulfate: After copper removal, the supernatant is concentrated by ultrafiltration and RO membrane, and the concentrate is evaporated and dried to obtain anhydrous sodium sulfate. Since iron and copper have been completely removed, the membrane clogging problem in the traditional process is avoided.

[0011] Preferably, in step 1, the aeration oxidation process uses a microporous aeration device, and the aeration volume is controlled to 0.5-1.0m 3 / (m 3 h) to ensure that ferrous hydroxide is fully exposed to oxygen and converted into ferric hydroxide.

[0012] Preferably, in step 2, the process of adjusting the pH with sulfuric acid is controlled in real time by an online pH monitor. When the pH of the solution is stabilized at 4.2±0.1, the stirring speed is maintained at 80-120 r / min for 15-20 minutes to promote complete precipitation of trivalent iron ions.

[0013] Preferably, in step 3, sodium hydroxide is used to adjust the pH to a range of 8.8-9.0, and anionic PAM with a molecular weight of 8 million to 12 million is added during the precipitation process in an amount of 5-10 mg / L to improve the flocculation efficiency of copper hydroxide.

[0014] Preferably, the filter cake washing process adopts a countercurrent washing method, the solid-liquid ratio of washing water to filter cake is (2-3):1, and the washing times are 2-3 times to ensure that the residual amount of soluble salt (such as sodium sulfate) in the filter cake is less than 0.5%.

[0015] Preferably, in step 4, the operating pressure of the RO membrane concentration is 1.0-1.5 MPa, the concentration multiple is controlled to be 5-8 times, and the evaporation drying temperature is set to 150-180° C. to obtain anhydrous sodium sulfate with a purity of ≥98%.

[0016] (3) Beneficial effects

[0017] Compared with the prior art, the present invention provides a process for removing iron and copper from iron-based copper plating wastewater, which has the following beneficial effects:

[0018] 1. The iron-based copper plating wastewater iron and copper removal utilization process includes the following beneficial effects:

[0019] Zero hazardous waste discharge: Iron and copper are separated through a two-step precipitation process, avoiding the generation of mixed hazardous waste. The filter cake is directly converted into iron sulfate and copper sulfate products, with no waste residue discharge.

[0020] High-efficiency separation and resource utilization: The separation rate of iron and copper exceeds 99% (see example data), and high-purity iron sulfate and copper sulfate are produced simultaneously, significantly improving economic benefits;

[0021] Improved process stability: The pre-oxidation step ensures that ferrous iron is completely converted into ferric iron, eliminating the risk of oxidation precipitation in subsequent processes, preventing clogging of membrane modules and ensuring smooth production.

[0022] Cost advantage: Aeration oxidation under alkaline conditions reduces the cost of oxidants (compared with sodium persulfate and hydrogen peroxide) and reduces the generation of secondary wastewater. DETAILED DESCRIPTION

[0023] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0024] The present invention provides a technical solution: a process for removing iron and copper from iron-based copper plating wastewater, comprising the following steps:

[0025] Step 1, pretreatment and oxidation: First, filter the wastewater to remove mechanical impurities, foam, etc., and then treat the mechanical impurities together with ordinary industrial waste after cleaning. Stir the filtrate and adjust the pH to 9.5-10.0 with liquid caustic soda. At the same time, introduce compressed air for full aeration and oxidation (you can also add sodium persulfate or slowly add hydrogen peroxide with stirring at pH 7-8, but aeration oxidation is considered for cost reasons). Pay attention to pH changes during the oxidation process to ensure that the pH is stable and not lower than 9.0. Aerate for about 1 hour until the black-green precipitate has completely turned yellow-brown and the divalent iron in it has been completely oxidized to trivalent iron;

[0026] Step 2, extracting ferric sulfate: slowly adjust with sulfuric acid and stabilize the solution at pH 4.1-4.3, preferably at pH 4.2 for more than 15 minutes, add PAM, stir evenly and let it settle, pump the bottom slurry into the filter press, and wash the filter cake with clean water to remove the soluble copper and sodium salts in the cake. The filtrate and washing water are returned to the raw water. The filter cake is ferric hydroxide, which can be directly used for the treatment of acidic wastewater and also has the function of precipitation flocculant. It can also be placed in a reactor, and concentrated sulfuric acid is slowly injected to dissolve the filter cake according to the iron content, heated to 60-80 ° C, stirred for 1-2 hours until completely dissolved, and cooled to obtain a ferric sulfate solution with an iron content of 9-12% (varies with the moisture content of the filter cake), which is used as a water treatment agent or other iron agent.

[0027] Step 3, extracting copper sulfate: the pH of the filtrate after the above iron removal is further adjusted to 8.5-9.0 with sodium hydroxide and maintained stable for more than 15 minutes, PAM is added and stirred, and the mixture is allowed to settle. The bottom slurry is pumped into a filter press for filtration, and the filter cake is washed with clean water to remove soluble salts in the cake. The filtrate and washing water are returned to the water after iron removal and before copper removal. The filter cake is placed in a reactor, and concentrated sulfuric acid of a corresponding amount is injected according to the copper content. The solution is stirred to dissolve all the precipitates, and the solution is cooled to obtain a copper sulfate solution with a copper content of 5-7.5%, which is used as a copper plating raw material or a copper sulfate solution from other sources;

[0028] Step 4: Concentration and evaporation to extract sodium sulfate: In the above process, since iron is trivalent, the iron and copper are basically completely removed after the copper removal process. The clear liquid is directly ultrafiltered into the RO membrane for concentration, and the concentrated liquid is evaporated and dried to obtain anhydrous sodium sulfate.

[0029] In the present invention, in order to avoid the problem of incomplete iron and copper separation and membrane clogging caused by incomplete oxidation, in step 1, a microporous aeration device is used in the aeration oxidation process, and the aeration volume is controlled to 0.5-1.0m 3 / (m 3 h) to ensure that ferrous hydroxide is fully exposed to oxygen and converted into ferric hydroxide. The use of microporous aeration devices and controlled aeration volume can increase the contact area between oxygen and wastewater and the reaction efficiency, ensuring that divalent iron is completely oxidized to trivalent iron, avoiding the subsequent problems of incomplete iron and copper separation and membrane clogging due to incomplete oxidation.

[0030] In the present invention, in order to improve the iron-copper separation efficiency and product purity, in step 2, the process of adjusting the pH with sulfuric acid is controlled in real time by an online pH monitor. When the pH of the solution is stabilized at 4.2±0.1, the stirring speed is maintained at 80-120 r / min and maintained for 15-20 minutes to promote complete precipitation of trivalent iron ions. The online pH monitor is used to control and maintain the stirring speed and time in real time, and the reaction conditions can be accurately controlled to ensure complete precipitation of trivalent iron ions, thereby improving the iron-copper separation efficiency and product purity.

[0031] In the present invention, in order to improve the copper ion recovery rate and separation purity, in step 3, the pH range of sodium hydroxide is adjusted to 8.8-9.0, and anionic PAM with a molecular weight of 8 million to 12 million is added during the precipitation process at a dosage of 5-10 mg / L to improve the flocculation efficiency of copper hydroxide. Limiting the pH range of sodium hydroxide and selecting a specific molecular weight PAM and dosage can optimize the copper hydroxide flocculation effect, accelerate the precipitation process, and improve the copper ion recovery rate and separation purity.

[0032] In the present invention, in order to reduce residual impurities, improve the purity of subsequent ferric sulfate and copper sulfate solutions, and save washing water, a countercurrent washing method is used in the filter cake washing process, the solid-liquid ratio of washing water to filter cake is (2-3):1, and the number of washings is 2-3 times, so as to ensure that the residual amount of soluble salts (such as sodium sulfate) in the filter cake is less than 0.5%. By adopting the countercurrent washing method, controlling the solid-liquid ratio and the number of washings, the soluble salts (such as sodium sulfate) in the filter cake can be efficiently removed, the residual impurities can be reduced, the purity of subsequent ferric sulfate and copper sulfate solutions can be improved, and washing water can be saved.

[0033] In the present invention, in order to avoid product impurities caused by iron and copper residues while optimizing energy consumption and production stability, in step 4, the operating pressure of the RO membrane concentration is 1.0-1.5 MPa, the concentration ratio is controlled to 5-8 times, and the evaporation drying temperature is set to 150-180° C. to obtain anhydrous sodium sulfate with a purity of ≥98%. Controlling the RO membrane operating pressure, concentration ratio, and evaporation temperature can ensure the concentration efficiency and purity of sodium sulfate, avoid product impurities caused by iron and copper residues, and optimize energy consumption and production stability.

[0034] Key control points:

[0035] Thorough oxidation: Ensure that divalent iron is completely oxidized to trivalent iron to avoid blockage in subsequent processes;

[0036] Precise pH control: Real-time pH adjustment is achieved through an online monitor to ensure efficient separation of iron and copper ions (e.g., at pH 4.2, ferric iron precipitation is most complete and copper ion solubility is highest);

[0037] Resource circulation: All washing water and filtrate are returned to the previous link to achieve zero discharge.

[0038] Example 1

[0039] Copper-plated welding wire wastewater: iron 1818 mg / L, copper 349 mg / L; after the above process treatment, liquid ferric sulfate is obtained: iron 11.57%, copper 0.073% (iron and copper account for 99.37% and 0.63%); copper sulfate solution: copper 6.42%, iron 0.029% (iron and copper account for 0.45% and 99.55%).

[0040] Example 2

[0041] Copper-plated welding wire wastewater: iron 628.02 mg / L, copper 168.41 mg / L; after the above process treatment and slightly concentrating the obtained solution, liquid ferric sulfate is obtained: iron 14.05%, copper 0.078% (the iron and copper account for 99.45% and 0.55%); copper sulfate solution: copper 7.38%, iron 0.034% (the iron and copper account for 0.44% and 99.56%).

[0042] Summarize:

[0043] Pre-oxidation staged precipitation process: ferrous iron is converted into ferric iron through aeration oxidation under alkaline conditions, achieving efficient separation of iron and copper ions, which is different from the traditional one-step co-precipitation process;

[0044] Precision pH control parameters: Achieve efficient precipitation of ferric iron and high solubility of copper ions within the pH range of 4.0-4.3, ensuring an iron-copper separation rate of >99%;

[0045] Alkaline aeration oxidation technology: Breaking through the traditional idea of ​​oxidation under acidic conditions, improving oxidation efficiency and reducing costs;

[0046] Direct acid dissolution process for filter cakes: Ferric hydroxide and copper hydroxide filter cakes are directly dissolved in concentrated sulfuric acid to prepare ferric sulfate and copper sulfate, avoiding secondary wastewater and additional separation costs.

[0047] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A process for removing iron and copper from iron-based copper plating wastewater, characterized by: The steps include: Step 1, pretreatment and oxidation: the wastewater is first physically filtered to remove mechanical impurities (such as drawing powder, foam, etc.), and the impurities are cleaned and then treated as ordinary industrial waste; The filtrate is stirred with liquid caustic soda to adjust its pH to 9.5-10.0, and compressed air is introduced for aeration oxidation for about 1 hour, during which the pH is maintained at ≥ 9.0, so that the black-green ferrous hydroxide precipitate is oxidized to a yellow-brown ferric hydroxide precipitate, ensuring that the divalent iron is completely converted to trivalent iron; Step 2, extracting ferric sulfate: adjusting the solution pH to 4.1-4.3 (preferably pH 4.2) with sulfuric acid, stabilizing for more than 15 minutes, and adding PAM for flocculation and precipitation; filtering the bottom slurry through a filter press, washing the filter cake with clean water to remove soluble copper and sodium salts, and returning the filtrate to the original water tank; transferring the filter cake (ferric hydroxide) into a reactor, adding concentrated sulfuric acid according to the iron content to dissolve it, heating to 60-80° C., stirring for 1-2 hours until completely dissolved, and cooling to obtain a ferric sulfate solution containing 9-12% iron, which can be used as a water treatment agent or iron supplement product; Step 3, extracting copper sulfate: After iron removal, the filtrate is adjusted to a pH of 8.5-9.0 with sodium hydroxide, stabilized for more than 15 minutes, and then PAM is added for flocculation and precipitation; the bottom slurry is filtered through a filter press, the filter cake is washed with clean water to remove soluble salts, and the filtrate is returned to the process before copper removal; the filter cake (copper hydroxide) is transferred to a reactor, concentrated sulfuric acid is added according to the copper content to dissolve it, and after cooling, a copper sulfate solution containing 5-7.5% copper is obtained, which can be used as a copper plating raw material or for other purposes; Step 4: Concentration and evaporation to extract sodium sulfate: After copper removal, the supernatant is concentrated by ultrafiltration and RO membrane, and the concentrate is evaporated and dried to obtain anhydrous sodium sulfate. Since iron and copper have been completely removed, the membrane clogging problem in the traditional process is avoided.

2. The process for removing iron and copper from iron-based copper plating wastewater according to claim 1, wherein: In step 1, the aeration oxidation process uses a microporous aeration device, and the aeration volume is controlled at 0.5-1.0m 3 / (m 3 h) to ensure that ferrous hydroxide is fully exposed to oxygen and converted into ferric hydroxide.

3. The process for removing iron and copper from iron-based copper plating wastewater according to claim 1, wherein: In step 2, the process of adjusting the pH with sulfuric acid is controlled in real time by an online pH monitor. When the pH of the solution is stabilized at 4.2±0.1, the stirring speed is maintained at 80-120 r / min for 15-20 minutes to promote the complete precipitation of trivalent iron ions.

4. The process for removing iron and copper from iron-based copper plating wastewater according to claim 1, wherein: In step 3, sodium hydroxide is used to adjust the pH to a range of 8.8-9.0, and anionic PAM with a molecular weight of 8 million to 12 million is added during the precipitation process in an amount of 5-10 mg / L to improve the flocculation efficiency of copper hydroxide.

5. The process for removing iron and copper from iron-based copper plating wastewater according to claim 1, wherein: The filter cake washing process adopts a countercurrent washing method, the solid-liquid ratio of washing water to filter cake is (2-3):1, and the washing times are 2-3 times to ensure that the residual amount of soluble salt (such as sodium sulfate) in the filter cake is less than 0.5%.

6. The process for removing iron and copper from iron-based copper plating wastewater according to claim 1, wherein: In step 4, the operating pressure of the RO membrane concentration is 1.0-1.5 MPa, the concentration multiple is controlled to be 5-8 times, and the evaporation drying temperature is set to 150-180° C. to obtain anhydrous sodium sulfate with a purity of ≥98%.