Method for treating electrogalvanizing wastewater by magnesium-carbon micro-electrolysis

Abstract

The invention relates to the technical field of wastewater treatment, in particular to a method for treating electrogalvanizing wastewater by magnesium-carbon micro-electrolysis, which comprises the following steps: (1) micro-electrolysis reaction: mixing the electrogalvanizing wastewater with magnesium-carbon powder, stirring, and carrying out solid-liquid separation to obtain filter residue 1 and filtrate 1; (2) flocculation and impurity removal: adding lime milk and ferrous sulfate into the filtrate 1, stirring, and carrying out solid-liquid separation to obtain filter residues 2 and filtrate 2; (3) deep purification: adjusting the pH value of the filtrate 2 to 10-12, stirring, and carrying out solid-liquid separation to obtain a filter residue 3 and a filtrate 3; and (4) zinc recovery: adjusting the pH value of the filtrate 3 to 9-10, stirring, carrying out settling separation, dissolving the underflow at the lower layer with sulfuric acid, adjusting the pH value to 5-6, and returning to the electrogalvanizing process for recycling. According to the method, the magnesium-carbon microelectrode is adopted to treat the electrogalvanizing wastewater, ions in the wastewater are subjected to electrolytic reduction to reduce the potential, then the zinc-rich solution is obtained through the coagulation impurity removal and deep purification process, and zinc resource recovery is achieved.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, and specifically to a method for treating electroplating zinc wastewater using magnesium-carbon micro-electrolysis. Background Technology

[0002] Electroplating zinc plating involves electrodepositing a zinc layer onto a metal substrate. Utilizing the sacrificial anode effect or passivation film of zinc, it effectively slows down the corrosion rate of the substrate, significantly extending product lifespan. However, the electroplating process generates a large amount of industrial wastewater, which contains high concentrations of zinc ions (Zn⁻). 2+ Nickel ions (Ni) are also introduced due to process requirements. 2+ ), copper ions (Cu) 2+ ) and chromium ions (Cr 6+ / Cr 3+ Heavy metal ions, such as α, β, and γ, are present. These heavy metal ions are non-biodegradable. If they are discharged directly without effective treatment, they will accumulate in water and soil, enter the human body through the food chain, and cause serious health risks such as chronic poisoning and organ damage. At the same time, they will cause irreversible damage to the ecosystem.

[0003] Currently, extensive research has been conducted on treatment methods for electroplating wastewater, resulting in various technical routes, mainly including chemical precipitation, adsorption, membrane separation, electrolysis, ferrite methods, and internal electrolysis. However, each method has significant limitations in practical applications, making it difficult to simultaneously achieve a balance between treatment efficiency, cost control, and environmental protection requirements. Among these, chemical precipitation is the most widely used traditional technology. It involves adding precipitants such as sodium hydroxide, sodium sulfide, and sodium carbonate to the wastewater, causing heavy metal ions to form hydroxides, sulfides, or carbonates, which are then removed through solid-liquid separation. While this method is simple and low-cost, it suffers from problems such as high sludge production, poor removal of organic pollutants, and difficulty in meeting the chemical oxygen demand (COD) standards for the treated effluent.

[0004] Adsorption methods remove pollutants by physically or chemically adsorbing heavy metal ions through the pore structure or functional groups on the surface of adsorbents such as activated carbon, zeolite, and mesoporous materials. This method offers high removal rates for low-concentration heavy metal ions and produces stable effluent quality. However, the adsorbents are highly selective, with most exhibiting high adsorption capacity only for a single or a few types of heavy metal ions. This makes it difficult to simultaneously remove other heavy metal ions coexisting in electroplating wastewater, necessitating multi-stage adsorption processes, which leads to complex procedures and increased costs. Membrane separation methods include ultrafiltration, nanofiltration, and reverse osmosis. These methods suffer from high equipment investment and operating costs. Membranes are also susceptible to fouling. Suspended solids, organic complexes, and high-valence metal ions in electroplating wastewater can form a fouling layer or undergo chemical adsorption on the membrane surface, leading to a decrease in membrane flux and a shortened membrane lifespan.

[0005] Electrolysis utilizes an external electric field to cause heavy metal ions to undergo a reduction reaction at the cathode and precipitate out, while an oxidation reaction occurs at the anode, forming flocs that adsorb pollutants. It has advantages such as high treatment efficiency, fast reaction speed, and no need to add chemical agents. However, energy consumption and operating costs are its main limiting factors, making it difficult to popularize in small and medium-sized electroplating enterprises.

[0006] The ferrite method utilizes the lattice structure of ferrite to encapsulate and fix heavy metal ions, followed by precipitation separation to achieve metal separation. This method has the advantage of good sludge stability, but still suffers from high sludge production. The internal electrolysis method (also known as the sacrificial anode method) uses two metals with different electrode potentials to form a galvanic cell. Pollutants are removed through spontaneous electrode reactions that generate redox reactions. However, the packing material is prone to oxidation and passivation, requiring periodic acid washing and activation, resulting in high maintenance costs. Currently, it is mainly used in small-scale, low-concentration electroplating wastewater treatment.

[0007] Besides the methods mentioned above, micro-electrolysis technology has received widespread attention in the field of industrial wastewater treatment in recent years. In micro-electrolysis technology, iron-carbon filler is currently the most widely used treatment agent in industry. It is usually made by sintering and granulating a mixture of cast iron filings and activated carbon, resulting in a low reusability rate. Moreover, granulated fillers also suffer from uneven component distribution, making it difficult to precisely control the amount of iron and carbon added to the wastewater, thus affecting the recovery efficiency of metal components from the wastewater.

[0008] Therefore, developing a treatment technology that can efficiently and simultaneously remove multiple heavy metal ions from wastewater and can operate stably under weakly acidic or near-neutral pH conditions is of great practical significance and industrial application value for promoting the green transformation of the electroplating industry and alleviating ecological and environmental pressures. Summary of the Invention

[0009] Currently, there is a lack of efficient methods for removing heavy metal ions from electroplating wastewater while reducing treatment costs and secondary pollution. This invention provides a method for treating electroplating wastewater using magnesium-carbon micro-electrolysis. This invention uses a uniformly mixed mixture of magnesium powder and carbon powder as the micro-electrolysis filler, eliminating the need for sintering and granulation. The amount of magnesium and carbon added is easily controlled. Furthermore, this method requires a small amount of magnesium and carbon powder; 1 g of magnesium and carbon powder can meet the treatment needs of 0.5–1 L of electroplating wastewater.

[0010] The technical solution of this invention is as follows: A method for treating electroplating wastewater using magnesium-carbon microelectrolysis includes the following steps: (1) Micro-electrolysis reaction: The zinc plating wastewater and magnesium carbon powder are mixed at a volume mass ratio of 0.5~1 L:1 g, and after stirring, solid-liquid separation is carried out to obtain filter residue 1 and filtrate 1. The pH value of the electroplating wastewater is 4.5~6.5, and the Zn content in the wastewater is... 2+ Concentration of 20~100 mg / L, Ni 2+ Concentrations range from 0.1 to 10 mg / L, Cu 2+ Concentrations range from 0.1 to 5 mg / L, Cr 6+ / Cr 3+ The concentration is 0.05~1 mg / L; Magnesium carbon powder is composed of magnesium powder and carbon powder in a mass ratio of 2 to 4:1; (2) Flocculation and impurity removal: Add lime milk and ferrous sulfate to filtrate 1, adjust the pH of the system to 7-8, stir and then perform solid-liquid separation to obtain filter residue 2 and filtrate 2; (3) Deep purification: Adjust the pH value of filtrate 2 to 10~12, stir and then perform solid-liquid separation to obtain filter residue 3 and filtrate 3; (4) Zinc recovery: Adjust the pH of filtrate 3 to 9-10, stir and then let it settle and separate. Dissolve the bottom layer with sulfuric acid, adjust the pH to 5-6, and return it to the electroplating zinc process for recycling.

[0011] Furthermore, the stirring speed of the micro-electrolysis reaction in step (1) is 300~500 rpm and the stirring time is 1.5~3 h.

[0012] Furthermore, in step (1), the magnesium carbon powder is pretreated before use to remove surface impurities and improve reaction activity.

[0013] Furthermore, in step (2), the concentration of lime slurry is 10%~20%.

[0014] Furthermore, in step (2), the amount of ferrous sulfate used is determined according to the ratio of iron to Cu in the electroplating wastewater. 2+ With Cr 6+ / Cr 3+ The total molar ratio is calculated to be 1 to 3:1.

[0015] Furthermore, in step (2), the stirring speed for flocculation and impurity removal is 600~800 rpm, and the stirring time is 1~3 h.

[0016] Furthermore, the stirring speed for deep purification in step (3) is 250~350 rpm, and the stirring time is 30~60 min.

[0017] Furthermore, in step (3), the pH value of filtrate 2 is adjusted using an aqueous sodium hydroxide solution with a concentration of 0.5~1 mol / L.

[0018] Furthermore, in step (4), the stirring speed for zinc recovery is 300-400 rpm and the stirring time is 20-40 min.

[0019] Furthermore, in step (4), the pH value of filtrate 3 is adjusted using dilute sulfuric acid with a concentration of 6~9 mol / L.

[0020] The beneficial effects of this invention are as follows: This invention utilizes magnesium-carbon microelectrodes to treat electroplating zinc wastewater. The ions in the wastewater are electrolytically reduced to lower the potential, followed by coagulation and deep purification processes to obtain a zinc-rich solution, thus achieving zinc resource recovery. This invention consumes less magnesium-carbon powder, further reducing reagent costs, and does not introduce new harmful substances, avoiding secondary pollution. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a process flow diagram of the method for treating electroplating zinc wastewater using magnesium-carbon micro-electrolysis according to Embodiment 1 of the present invention. Detailed Implementation

[0023] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions in the embodiments of this invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this invention.

[0024] This invention achieves the treatment and resource recovery of electroplating wastewater through four steps: magnesium-carbon micro-electrolysis, flocculation and impurity removal, deep purification, and zinc recovery. Specifically, the steps include the following: (1) Micro-electrolysis reaction: The zinc plating wastewater is mixed with magnesium carbon powder (composed of magnesium powder and carbon powder), and after stirring and reacting for a period of time, solid-liquid separation is performed to obtain filter residue 1 and filtrate 1. In order to recover zinc from the zinc plating wastewater, the amount of magnesium carbon powder added needs to be controlled. Generally, a small amount of magnesium carbon powder is used. At this time, the main component of filter residue 1 is magnesium carbon powder, which can be used for the micro-electrolysis treatment of the next batch of zinc plating wastewater; the main component of filtrate 1 is a mixture of low-potential reduced heavy metal ions.

[0025] (2) Flocculation and impurity removal: Lime milk and ferrous sulfate were added to filtrate 1, and after stirring for a period of time, solid-liquid separation was performed to obtain filter residue 2 and filtrate 2. Filter residue 2 is a mixture of copper hydroxide, chromium hydroxide, and ferric hydroxide; filtrate 2 is wastewater after the removal of copper and chromium ions. The Cu in filtrate 2 is... 2+ The concentration can reach levels below 0.1 mg / L, and the chromium concentration can reach levels below 0.05 mg / L.

[0026] (3) Deep purification: Adjust the pH of filtrate 2 to 10-12, stir for a period of time, and then perform solid-liquid separation to obtain filter residue 3 and filtrate 3. Filter residue 3 is a mixture of magnesium hydroxide and nickel hydroxide; the main component of filtrate 3 is [Zn(OH)4]. 2- .

[0027] (4) Zinc recovery: Adjust the pH of filtrate 3 to 9-10, stir for a period of time and then let it settle and separate. The upper clear liquid can be reused as recycled water, and the lower bottom liquid is dissolved with sulfuric acid and the pH is adjusted to 5-6 and returned to the electroplating zinc process for recycling.

[0028] The method of this invention is applicable to contents containing zinc ions (Zn). 2+ Nickel ions (Ni) 2+ ), copper ions (Cu) 2+ ) and chromium ions (Cr 6+ / Cr 3+ In some embodiments of this invention, for electroplating wastewater containing various heavy metal ions such as zinc oxide and zinc ions, the pH value and heavy metal ion concentration of the wastewater need to be adjusted before treatment with magnesium carbon powder to ensure that the pH value is between 4.5 and 6.5 and the Zn concentration is within the specified range. 2+ Concentration of 20~100 mg / L, Ni 2+ Concentrations range from 0.1 to 10 mg / L, Cu 2+ Concentrations range from 0.1 to 5 mg / L, Cr 6+ / Cr 3+ The concentration is 0.05~1 mg / L.

[0029] The Cr mentioned in this invention 6+ / Cr 3+ It refers to the collective term for Cr ions in two valence states in a liquid.

[0030] In some embodiments of the present invention, the mass ratio of magnesium powder to carbon powder in magnesium carbon powder is 2~4:1.

[0031] In some embodiments of the present invention, electroplating wastewater and magnesium carbon powder are mixed at a volume-to-mass ratio of 0.5~1 L:1 g. This ratio range can ensure that the electroplating wastewater and magnesium carbon powder are in full contact, and ensure that the micro-electrolysis reaction is thorough.

[0032] In some embodiments of the present invention, the stirring speed of the micro-electrolysis reaction in step (1) is 300~500 rpm and the stirring time is 1.5~3 h.

[0033] When the stirring speed is less than 300 rpm, wastewater and magnesium carbon powder are prone to stratification, resulting in low solid-liquid mass transfer efficiency, excessively high concentrations of heavy metal ions in localized areas, and incomplete reaction. When the stirring speed is greater than 500 rpm, it intensifies the collision and wear between magnesium powder particles, leading to excessively small particle size, increasing the difficulty of subsequent solid-liquid separation, and also increasing energy consumption. A stirring speed of 300~500 rpm can achieve efficient mass transfer, avoiding excessive wear of magnesium powder and energy waste.

[0034] Commercially available magnesium powder is prone to forming an oxide film on its surface, and carbon powder may have impurities such as oil and dust adhering to its surface. The oxide film can block the direct contact between magnesium powder and wastewater, reducing the anodic electron release efficiency. Impurities can affect the conductivity of carbon powder, leading to obstructed electron transfer in the micro-electrolysis system and a decrease in overall reaction activity. Based on this, in some embodiments of the present invention, in step (1), magnesium carbon powder is first pretreated before use, for example, by acid washing to remove the magnesium powder oxide film, water washing to remove carbon powder impurities, etc., to remove surface impurities, expose the fresh surface of magnesium powder, improve the conductivity of carbon powder, ensure the electron transfer efficiency of the magnesium carbon micro-electrolysis system, stabilize the micro-electrolysis reaction activity, and avoid fluctuations in the treatment effect caused by impurities.

[0035] In some embodiments of the present invention, in step (2), the concentration of lime milk is 10% to 20%, and the main function of lime milk is to adjust the pH value of the system. The amount added is determined according to the original pH value of filtrate 1.

[0036] In some embodiments of the present invention, in step (2), the amount of ferrous sulfate used is based on the ratio of iron to Cu in the electroplating wastewater. 2+ With Cr 6+ / Cr 3+ The total molar ratio is calculated to be 1 to 3:1.

[0037] In some embodiments of the present invention, the stirring speed of step (2) flocculation and impurity removal is 600~800 rpm and the stirring time is 1~3 h.

[0038] For flocculation and impurity removal, lime slurry, ferrous sulfate, and filtrate 1 must be thoroughly mixed. If the stirring speed is less than 600 rpm, the reagents will be unevenly dispersed, making it difficult for stable flocs to form locally. If the stirring speed is greater than 800 rpm, the existing flocs will be destroyed, preventing fine particles from settling. A stirring speed of 600-800 rpm can achieve a balance between uniform reagent dispersion and stable floc formation.

[0039] In some embodiments of the present invention, the stirring speed of the deep purification step (3) is 250~350 rpm and the stirring time is 30~60 min.

[0040] Step (3) involves using a high pH value to remove residual trace heavy metal ions (such as Zn) from filtrate 2. 2+ Ni 2+ Hydroxide precipitates are formed. Therefore, if the stirring speed is >350 rpm, the fine precipitate particles that have already formed will be suspended and difficult to settle; if the stirring speed is <250 rpm, there will be a stirring dead zone, and local residual heavy metal ions will not be able to precipitate.

[0041] In some embodiments of the present invention, in step (3), an alkaline substance is used to adjust the pH value of the filtrate 2. The alkaline substance is selected from one or more of sodium hydroxide, potassium hydroxide or sodium carbonate, wherein a sodium hydroxide aqueous solution with a concentration of 0.5~1 mol / L is preferred.

[0042] In some embodiments of the present invention, the stirring speed for step (4) of zinc recovery is 300-400 rpm and the stirring time is 20-40 min.

[0043] Step (4) promotes the growth of [Zn(OH)4] through stirring. 2- The Zn(OH)2 flocs are converted into Zn(OH)2 precipitate. If the stirring speed is too fast, the shear force generated by the fluid may exceed the structural strength of the flocs, breaking up the already aggregated Zn(OH)2 flocs and redispersing them into fine particles, making sedimentation and separation difficult. If the stirring speed is too slow, similarly, some [Zn(OH)4] may be lost. 2- It cannot be dissociated and transformed.

[0044] In some embodiments of the present invention, in step (4), an acidic substance is used to adjust the pH value of the filtrate 3, such as hydrochloric acid, sulfuric acid, nitric acid, etc. From the perspective of not introducing new impurities, dilute sulfuric acid with a concentration of 6~9 mol / L is preferred to adjust the pH value of the filtrate 3.

[0045] In many steps of this invention, solid-liquid separation processes are involved, and solid-liquid separation can be achieved by filtration, such as using filter paper, filter membrane, or filter screen for filtration, and using normal pressure, reduced pressure, or vacuum conditions for filtration. In some embodiments of this invention, steps (1), (2), and (3) of this invention can all be achieved by centrifugal filtration.

[0046] Example 1 (1) Micro-electrolysis reaction: Take 100 L of electroplating wastewater with a pH of 5.0, Zn 2+ The concentration is 50 mg / L, Ni 2+ The concentration is 5 mg / L, Cu 2+ The concentration is 3 mg / L, Cr 6+ / Cr 3+The concentration was 0.5 mg / L. Wastewater and magnesium carbon powder were mixed at a volume-to-mass ratio of 0.5 L: 1 g, i.e., 200 g of magnesium carbon powder was added. The magnesium carbon powder was prepared by uniformly mixing magnesium powder and carbon powder at a mass ratio of 2:1. After reacting at a stirring speed of 300 rpm for 1.5 h, centrifugation and filtration were performed to obtain filter residue 1 and filtrate 1. Filter residue 1 mainly consists of magnesium carbon powder and can be reused; filtrate 1 mainly consists of a mixture of low-potential reduced heavy metal ions.

[0047] (2) Flocculation and impurity removal: Add 10% lime milk and ferrous sulfate to filtrate 1. The amount of ferrous sulfate is based on the ratio of iron to Cu in the wastewater. 2+ With Cr 6+ / Cr 3+ The total molar ratio was calculated at 1:1. The amount of lime slurry was determined to adjust the pH of the system to 7.0. The stirring speed was 600 rpm. After reacting for 1 h, solid-liquid separation was performed to obtain filter residue 2 and filtrate 2. Filter residue 2 was a mixture of copper hydroxide, chromium hydroxide, and iron hydroxide. Filtrate 2 contained Cu... 2+ The concentration is below 0.1 mg / L, and the chromium concentration is below 0.05 mg / L.

[0048] (3) Deep purification: The pH of filtrate 2 was further adjusted to 12 with 0.5 mol / L sodium hydroxide, and the mixture was stirred at 300 rpm for 30 min. Solid-liquid separation was performed again to obtain filter residue 3 and filtrate 3. Filter residue 3 is a mixture of magnesium hydroxide and nickel hydroxide, and the main component of filtrate 3 is [Zn(OH)4]. 2- .

[0049] (4) Zinc recovery: Adjust the pH of filtrate 3 to 9.5 with 6 mol / L dilute sulfuric acid, stir at 300 rpm for 20 min, and after sedimentation and separation, the upper clear liquid can be reused as recycled water, and the lower bottom flow is dissolved with sulfuric acid, the pH is adjusted to 5.0, and returned to the electroplating zinc process for recycling.

[0050] Example 2 (1) Micro-electrolysis reaction: Take 100 L of electroplating wastewater with a pH of 6.5, Zn 2+ The concentration is 100 mg / L, Ni 2+ The concentration is 10 mg / L, Cu 2+ The concentration is 5 mg / L, Cr 6+ / Cr 3+The concentration was 1 mg / L. Wastewater and magnesium carbon powder were mixed at a volume-to-mass ratio of 1 L:1 g, i.e., 100 g of magnesium carbon powder was added. The magnesium carbon powder was prepared by uniformly mixing magnesium powder and carbon powder at a mass ratio of 4:1. After reacting for 3 h at a stirring speed of 500 rpm, the mixture was centrifuged and filtered to obtain filter residue 1 and filtrate 1. Filter residue 1 mainly consisted of magnesium carbon powder and could be reused; filtrate 1 mainly consisted of a mixture of low-potential reduced heavy metal ions.

[0051] (2) Flocculation and impurity removal: Add 20% lime milk and ferrous sulfate to filtrate 1. The amount of ferrous sulfate is based on the ratio of iron to Cu in the wastewater. 2+ With Cr 6+ / Cr 3+ The total molar ratio was calculated to be 3:1. The amount of lime slurry was determined by adjusting the pH of the system to 8.0. The stirring speed was 800 rpm, and the reaction was carried out for 3 hours. Solid-liquid separation was then performed to obtain filter residue 2 and filtrate 2. Filter residue 2 was a mixture of copper hydroxide, chromium hydroxide, and iron hydroxide. Filtrate 2 contained Cu. 2+ The concentration is below 0.1 mg / L, and the chromium concentration is below 0.05 mg / L.

[0052] (3) Deep purification: The pH of filtrate 2 was further adjusted to 10 with 1 mol / L sodium hydroxide, and the mixture was stirred at 250 rpm for 60 min. Solid-liquid separation was performed again to obtain filter residue 3 and filtrate 3. Filter residue 3 is a mixture of magnesium hydroxide and nickel hydroxide, and the main component of filtrate 3 is [Zn(OH)4]. 2- .

[0053] (4) Zinc recovery: Adjust the pH of filtrate 3 to 10 with 9 mol / L dilute sulfuric acid, stir at 400 rpm for 40 min, and after sedimentation and separation, the upper clear liquid can be reused as recycled water, and the lower bottom flow is dissolved with sulfuric acid and the pH is adjusted to 6.0 and returned to the electroplating zinc process for recycling.

[0054] Example 3 (1) Micro-electrolysis reaction: Take 100 L of electroplating wastewater with a pH of 4.5, Zn 2+ The concentration is 20 mg / L, Ni 2+ The concentration is 1 mg / L, Cu 2+ The concentration is 1 mg / L, Cr 6+ / Cr 3+The concentration was 0.05 mg / L. Wastewater and magnesium carbon powder were mixed at a volume-to-mass ratio of 0.8 L:1 g, i.e., 125 g of magnesium carbon powder was added. The magnesium carbon powder was prepared by uniformly mixing magnesium powder and carbon powder at a mass ratio of 3:1. After reacting for 2 hours at a stirring speed of 400 rpm, the mixture was centrifuged and filtered to obtain filter residue 1 and filtrate 1. Filter residue 1 mainly consisted of magnesium carbon powder and could be reused; filtrate 1 mainly consisted of a mixture of low-potential reduced heavy metal ions.

[0055] (2) Flocculation and impurity removal: Add 15% lime milk and ferrous sulfate to filtrate 1. The amount of ferrous sulfate is based on the ratio of iron to Cu in the wastewater. 2+ With Cr 6+ / Cr 3+ The total molar ratio was calculated to be 2:1. The amount of lime slurry was determined by adjusting the pH of the system to 7.5. The stirring speed was 700 rpm. After reacting for 2 hours, solid-liquid separation was performed to obtain filter residue 2 and filtrate 2. Filter residue 2 was a mixture of copper hydroxide, chromium hydroxide, and iron hydroxide. Filtrate 2 contained Cu... 2+ The concentration is below 0.1 mg / L, and the chromium concentration is below 0.05 mg / L.

[0056] (3) Deep purification: The pH of filtrate 2 was further adjusted to 12 with 0.8 mol / L sodium hydroxide, and the mixture was stirred at 350 rpm for 45 min. Solid-liquid separation was performed again to obtain filter residue 3 and filtrate 3. Filter residue 3 is a mixture of magnesium hydroxide and nickel hydroxide, and the main component of filtrate 3 is [Zn(OH)4]. 2- .

[0057] (4) Zinc recovery: Adjust the pH of filtrate 3 to 9 with 7 mol / L dilute sulfuric acid, stir at 350 rpm for 30 min, and after sedimentation and separation, the upper clear liquid can be reused as recycled water, and the lower bottom flow is dissolved with sulfuric acid and the pH is adjusted to 5.5 and returned to the electroplating zinc process for recycling.

[0058] Example 4 (1) Micro-electrolysis reaction: Take 100 L of electroplating wastewater with a pH of 5.5, Zn 2+ The concentration is 70 mg / L, Ni 2+ The concentration is 8 mg / L, Cu 2+ The concentration is 4 mg / L, Cr 6+ / Cr 3+The concentration was 0.8 mg / L. Wastewater and magnesium carbon powder were mixed at a volume-to-mass ratio of 0.6 L:1 g, i.e., 166.67 g of magnesium carbon powder was added. The magnesium carbon powder was prepared by uniformly mixing magnesium powder and carbon powder at a mass ratio of 2.5:1. After reacting at a stirring speed of 350 rpm for 2.5 h, centrifugation and filtration were performed to obtain filter residue 1 and filtrate 1. Filter residue 1 mainly consists of magnesium carbon powder and can be reused; filtrate 1 mainly consists of a mixture of low-potential reduced heavy metal ions.

[0059] (2) Flocculation and impurity removal: Add lime milk with a concentration of 12% and ferrous sulfate to filtrate 1. The amount of ferrous sulfate is based on the ratio of iron to Cu in the wastewater. 2+ With Cr 6+ / Cr 3+ The total molar ratio was calculated to be 1.5:1. The amount of lime slurry was determined by adjusting the pH of the system to 7.2. The stirring speed was 650 rpm, and the reaction was carried out for 1.5 h. Solid-liquid separation was then performed to obtain filter residue 2 and filtrate 2. Filter residue 2 was a mixture of copper hydroxide, chromium hydroxide, and iron hydroxide. Filtrate 2 contained Cu... 2+ The concentration is below 0.1 mg / L, and the chromium concentration is below 0.05 mg / L.

[0060] (3) Deep purification: The pH of filtrate 2 was further adjusted to 12 with 0.6 mol / L sodium hydroxide, and the mixture was stirred at 300 rpm for 30 min. Solid-liquid separation was performed again to obtain filter residue 3 and filtrate 3. Filter residue 3 is a mixture of magnesium hydroxide and nickel hydroxide, and the main component of filtrate 3 is [Zn(OH)4]. 2- .

[0061] (4) Zinc recovery: Adjust the pH of filtrate 3 to 9.8 with 8 mol / L dilute sulfuric acid, stir at 300 rpm for 20 min, and after sedimentation and separation, the upper clear liquid can be reused as recycled water, and the lower bottom flow is dissolved with sulfuric acid, the pH is adjusted to 5.8, and returned to the electroplating zinc process for recycling.

[0062] For Examples 1 to 4 above, the magnesium carbon powder used in the micro-electrolysis reaction in step (1) was replaced with iron carbon powder, and comparative experiments were conducted under the condition that other conditions remained unchanged. The results showed that when the reaction time was the same as in Example 1, the treatment effect of the electroplating wastewater using iron carbon powder was poor, and the overall reaction efficiency of magnesium carbon powder was about 2 to 3 times that of iron carbon powder.

[0063] Although the present invention has been described in detail by way of preferred embodiments, the present invention is not limited thereto. Various equivalent modifications or substitutions can be made to the embodiments of the present invention by those skilled in the art without departing from the spirit and essence of the invention, and such modifications or substitutions should all be within the scope of the present invention. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should also be covered within the protection scope of the present invention.

Claims

1. A method for treating electroplating wastewater using magnesium-carbon micro-electrolysis, characterized in that, Includes the following steps: (1) Micro-electrolysis reaction: The zinc plating wastewater and magnesium carbon powder are mixed at a volume mass ratio of 0.5~1 L:1 g, and after stirring, solid-liquid separation is carried out to obtain filter residue 1 and filtrate 1. The pH value of the electroplating wastewater is 4.5~6.5, and the Zn content in the wastewater is... 2+ Concentration of 20~100 mg / L, Ni 2+ Concentrations range from 0.1 to 10 mg / L, Cu 2+ Concentrations range from 0.1 to 5 mg / L, Cr 6+ / Cr 3+ The concentration is 0.05~1 mg / L; Magnesium carbon powder is composed of magnesium powder and carbon powder in a mass ratio of 2 to 4:1; (2) Flocculation and impurity removal: Add lime milk and ferrous sulfate to filtrate 1, adjust the pH of the system to 7-8, stir and then perform solid-liquid separation to obtain filter residue 2 and filtrate 2; (3) Deep purification: Adjust the pH value of filtrate 2 to 10~12, stir and then perform solid-liquid separation to obtain filter residue 3 and filtrate 3; (4) Zinc recovery: Adjust the pH of filtrate 3 to 9-10, stir and then let it settle and separate. Dissolve the bottom layer with sulfuric acid, adjust the pH to 5-6, and return it to the electroplating zinc process for recycling.

2. The method for treating electroplating wastewater using magnesium-carbon micro-electrolysis as described in claim 1, characterized in that, The stirring speed for step (1) micro-electrolysis reaction is 300~500 rpm and the stirring time is 1.5~3 h.

3. The method for treating electroplating wastewater using magnesium-carbon micro-electrolysis as described in claim 1, characterized in that, In step (2), the concentration of lime slurry is 10%~20%.

4. The method for treating electroplating wastewater using magnesium-carbon micro-electrolysis as described in claim 1, characterized in that, In step (2), the amount of ferrous sulfate used is based on the ratio of iron to Cu in the electroplating wastewater. 2+ With Cr 6+ / Cr 3+ The total molar ratio is calculated to be 1 to 3:

1.

5. A method for treating electroplating wastewater using magnesium-carbon micro-electrolysis as described in claim 1, characterized in that, Step (2) The stirring speed for flocculation and impurity removal is 600~800 rpm and the stirring time is 1~3 h.

6. A method for treating electroplating wastewater using magnesium-carbon micro-electrolysis as described in claim 1, characterized in that, Step (3) The stirring speed for deep purification is 250~350 rpm and the stirring time is 30~60 min.

7. A method for treating electroplating wastewater using magnesium-carbon micro-electrolysis as described in claim 1, characterized in that, In step (3), the pH value of filtrate 2 is adjusted using an aqueous sodium hydroxide solution with a concentration of 0.5~1 mol / L.

8. A method for treating electroplating wastewater using magnesium-carbon micro-electrolysis as described in claim 1, characterized in that, Step (4) The stirring speed for zinc recovery is 300~400 rpm and the stirring time is 20~40 min.

9. A method for treating electroplating wastewater using magnesium-carbon micro-electrolysis as described in claim 1, characterized in that, In step (4), the pH value of filtrate 3 is adjusted using dilute sulfuric acid with a concentration of 6~9 mol / L.

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