A copper recovery method for low-concentration circuit board copper-containing wastewater

Abstract

The application belongs to the technical field of metal recovery, and specifically relates to a copper recovery method for low-concentration copper-containing wastewater from circuit boards, which specifically comprises: pretreatment and complex breaking, chelation adsorption enrichment, low-voltage electrolysis, deep purification and reuse, and tail liquid full circulation. After the wastewater is filtered by a bag filter, a high-efficiency composite complex breaking agent is added to convert the complex copper into free copper; then the free copper is adsorbed by two-stage macroporous amino phosphonic acid type chelating resins, and high-concentration enrichment liquid is obtained through reverse flow regeneration of dilute hydrochloric acid; the enrichment liquid is subjected to low-voltage electrolysis, and electronic-grade copper sheets with a purity of greater than or equal to 99.5% are deposited on the cathode; the adsorption effluent is treated by an activated carbon filter and a security filter and then is reused for a production line, and the tail liquid is treated by a cation exchange resin to achieve zero discharge. The method has high copper recovery efficiency, high product purity, reusable wastewater, low energy consumption, environmental protection, no dangerous waste generation, and is suitable for resource treatment of circuit board copper-containing wastewater with different concentrations.

Description

Technical Field

[0001] This invention relates to the field of industrial wastewater treatment technology, specifically a method for copper recovery from low-concentration copper-containing wastewater from circuit boards. Background Technology

[0002] The etching, micro-etching, pickling, and board cleaning processes in PCB manufacturing generate a large amount of low to medium concentration copper-containing wastewater with copper ion concentrations ranging from 50 mg / L to 1 g / L. This type of wastewater is characterized by large volume, copper ion content between low-concentration rinsing water and high-concentration etching wastewater, and often contains complexing agents such as citric acid, EDTA, and ammonia, forming highly stable complexed copper. It is a typical wastewater that is difficult to treat and causes serious resource loss in the PCB industry.

[0003] Currently, traditional treatment and copper recovery processes for copper-containing wastewater in this concentration range have the following technical drawbacks: 1. Chemical precipitation: Requires the addition of large amounts of liquid alkali, sodium sulfide, and other reagents, easily generating large amounts of copper-containing hazardous sludge. Sludge disposal costs are high, and complexed copper cannot be completely precipitated, making it difficult to stably achieve ≤0.3 mg / L copper ions in the effluent, resulting in complete copper resource waste; 2. Conventional ion exchange: Resin adsorption capacity is limited. For copper ion concentrations of 50 mg / L-1 g / L, frequent resin regeneration is necessary, resulting in large amounts of regeneration wastewater, easily causing secondary pollution. Copper recovery purity is low, making high-value utilization impossible; 3. Direct electrolysis: This concentration... 4. Copper electrolysis: Low current efficiency, high energy consumption, slow electrolytic deposition rate, and problems such as low purity of electrolytic copper and scaling of electrode plates are prone to occur, making it impossible to operate continuously in industrial applications; 5. Membrane separation: High equipment investment, membrane modules are easily clogged by organic matter and copper ions, high operation and maintenance costs, and the concentrate still needs further treatment. It can only concentrate and cannot directly recover copper, resulting in poor economic efficiency; 6. Existing combined processes: They cannot be adapted to the characteristics of wastewater with concentrations in the range of 50mg / L-1g / L. They either have low treatment efficiency or excessive energy and chemical consumption, making it difficult to simultaneously achieve the goals of efficient copper recovery, effluent compliant for reuse, and no secondary pollution. The copper recovery rate is generally below 92%, and water resources cannot be recycled.

[0004] In summary, existing technologies cannot meet the treatment requirements for low-to-medium concentration copper-containing wastewater from circuit boards, ranging from 50 mg / L to 1 g / L.

[0005] Therefore, it is necessary to study a copper recovery method that is highly efficient, produces high-purity products, allows for wastewater reuse, has low energy consumption and is environmentally friendly, and generates no hazardous waste. Summary of the Invention

[0006] Therefore, it is necessary to provide a method for copper recovery from low-to-medium concentration copper-containing wastewater (50mg / L-1g / L) from circuit boards. This method utilizes a synergistic process of precise complex breaking, multi-stage chelation enrichment, gentle electrolytic purification, and deep wastewater purification to specifically address the pain points in wastewater treatment within this concentration range. This achieves efficient copper ion recovery and wastewater recycling, reduces treatment costs, eliminates secondary pollution, and meets the requirements of environmental protection management and resource recycling.

[0007] The technical solution of the present invention to solve the above-mentioned technical problems is as follows:

[0008] A method for copper recovery and resource reuse from copper-containing wastewater from circuit boards includes the following steps:

[0009] Step S1, Wastewater pretreatment and complex breaking treatment: Filter the copper-containing wastewater to remove impurities, add a complex breaking agent and stir to react, so that the complexed copper in the wastewater is converted into free copper ions;

[0010] Step S2, chelation adsorption enrichment: The wastewater treated in step S1 is adsorbed through an adsorption unit filled with chelating resin. Copper ions are selectively adsorbed, and the concentration of copper ions in the effluent is ≤0.1mg / L. When the chelating resin is saturated, it is regenerated using a dilute acid solution as a regenerator to obtain a high-concentration copper salt enriched solution.

[0011] Step S3, electrolytic recovery of copper: The high-concentration copper salt enrichment solution is electrolyzed, and electrolytic copper is deposited at the cathode. The tail liquid after electrolysis is returned to step S2 for recycling.

[0012] Step S4, Deep purification and reuse: The adsorbed water from step S2 is purified and reused in the production process after being adsorbed by activated carbon and filtered by precision.

[0013] Step S5, tail liquid treatment: The system tail liquid is treated with ion exchange resin and then reused to achieve zero wastewater discharge.

[0014] Furthermore, the copper ion concentration of the copper-containing wastewater in step S1 is 50 mg / L to 1 g / L. Pretreatment uses a 10 μm bag filter to remove suspended solids, ink debris, resin powder, and other impurities.

[0015] Further, the complex-breaking agent mentioned in step S1 is a high-efficiency composite complex-breaking agent, whose components, by mass percentage, include: sodium persulfate 12%–18%, polyferric sulfate 6%–10%, sodium gluconate 4%–6%, and the balance being deionized water. This composite complex-breaking agent utilizes the oxidizing properties of sodium persulfate, the synergistic effect of polyferric sulfate in complex-breaking and flocculation, and the synergistic activation effect of sodium gluconate to completely destroy the coordination structure of stable complexes such as Cu-EDTA and Cu-tartaric acid under normal temperature and pressure, completely converting the complexed copper into free copper ions. The preferred dosage of the composite complex-breaking agent is 1.5%–3% of the total mass of the wastewater; the reaction conditions are: normal temperature and pressure, stirring speed 250–350 r / min, reaction time 25–35 min, and adjusting the pH of the wastewater to 5.0–6.5.

[0016] Further, the adsorption unit in step S2 is a two-stage chelating resin adsorption tower connected in series, filled with macroporous aminophosphonic acid chelating resin. This resin has specific selective adsorption properties for copper ions, effectively eliminating interference from coexisting ions such as alkali metals and alkaline earth metals. During the adsorption process, the wastewater flow rate through the tower is controlled at 1.5–3 BV / h, and continuous adsorption is carried out at room temperature. After two stages of adsorption, the copper ion concentration in the effluent is ≤0.1 mg / L. When the resin is saturated, a 10%–15% (w / w) dilute hydrochloric acid solution is used as a regenerator, and countercurrent regeneration is performed at a flow rate of 1–1.5 BV / h for 30–45 min. The resulting solution is a copper chloride enriched solution with a copper ion concentration of 30–40 g / L.

[0017] Furthermore, step S3 electrolysis employs a low-pressure inert electrolytic cell, with the anode being a titanium-based ruthenium-iridium plated alloy and the cathode being a 316L stainless steel plate. The electrolysis process parameters are: electrolysis temperature 30–40℃, electrolysis voltage 1.2–1.8V, current density 80–110A / m², and electrolysis time 4–6h. Under these low-pressure and mild conditions, impurity co-deposition and severe hydrogen evolution are effectively suppressed, promoting the selective reduction and deposition of copper ions at the cathode to form dense, high-purity electrolytic copper sheets with a copper purity ≥99.5%, which can be directly reused as electronic-grade copper raw material. After electrolysis, the copper ion concentration in the tail liquid drops to 2–4 g / L. This tail liquid is entirely recycled to the resin regeneration process in step S2 as a replenishing solution for the regenerator, achieving closed-loop utilization of the regenerated liquid.

[0018] Furthermore, in step S4, the adsorbed water sequentially passes through a granular coconut shell activated carbon adsorption tower and a precision security filter with a filtration accuracy of 5μm to remove trace organic matter, color, and residual suspended solids from the wastewater. The resulting purified reclaimed water meets the following quality standards: copper ions ≤0.1mg / L, COD ≤50mg / L, and conductivity ≤200μS / cm, fully complying with the production water standards for circuit board surface cleaning, acid washing, rinsing, and cooling circulation. It can be directly reused in the corresponding processes, achieving a closed-loop water resource recycling system.

[0019] Furthermore, in step S5, the small amount of tail liquid generated by the system, such as activated carbon backwash drainage, is subjected to deep fine treatment with cation exchange resin to further remove trace amounts of residual copper ions. All the effluent is reused in the activated carbon backwashing process or the production cleaning process, with no wastewater discharged externally, achieving zero wastewater discharge for the entire system.

[0020] Compared with existing technologies, the copper recovery method for low-concentration copper-containing wastewater from circuit boards provided by this invention has the following characteristics:

[0021] First, a highly efficient composite complex-breaking agent with a specific ratio is used to completely destroy copper complexes under mild conditions, releasing free copper ions. Then, a macroporous aminophosphonic acid chelating resin is used to selectively adsorb copper ions in a two-stage series, reducing the copper ion concentration in the effluent to below 0.1 mg / L. Simultaneously, a high-concentration copper chloride enrichment solution of 30–40 g / L is obtained through acid regeneration. Further, low-pressure and mild electrolysis conditions are used to effectively inhibit the co-deposition of impurities, directly producing electronic-grade high-purity copper sheets with a purity ≥99.5%. The electrolysis tail liquid is recycled for resin regeneration, and the adsorbed effluent is reused in production after deep purification. The system tail liquid is also fully reused after cation exchange purification. This achieves high-value recovery of copper from medium- and low-concentration copper-containing wastewater, full reuse of water resources, and zero wastewater discharge, resulting in good economic and environmental benefits. Attached Figure Description

[0022] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a flowchart of the method in Embodiment 1 of the present invention. Detailed Implementation

[0024] It should be noted that, unless otherwise specified, the embodiments and features described in the embodiments of the present invention can be combined with each other. The technical solutions of the present invention will be further described below with reference to the accompanying drawings of the embodiments of the present invention. The present invention is not limited to the following specific embodiments.

[0025] Existing technologies cannot meet the treatment requirements of low-concentration copper-containing wastewater from circuit boards. Therefore, a copper recovery method with high copper recovery efficiency, high product purity, reusable wastewater, low energy consumption, environmentally friendly process, and no hazardous waste generation has been developed. The specific scheme is as follows:

[0026] Example 1

[0027] The wastewater contains copper ions with a concentration of 200 mg / L, of which complexed copper accounts for about 35%, COD 120 mg / L, suspended solids 80 mg / L, and pH 3.5.

[0028] like Figure 1 As shown, in step S1, pretreatment and complex breaking: the wastewater is pumped into a 10μm bag filter to remove suspended solids, ink debris, etc., reducing the suspended solids in the effluent to below 5mg / L. A high-efficiency composite complex breaking agent is added to the filtered wastewater, consisting of: 15% sodium persulfate, 8% polyferric sulfate, 5% sodium gluconate, and the remainder being deionized water. The dosage is 2% of the total wastewater mass. The reaction is carried out for 30 minutes under stirring speed of 300r / min and normal temperature and pressure conditions, and the pH is adjusted to 6.0 with sodium hydroxide solution. After the complex breaking reaction, all the complexed copper is converted into free copper ions.

[0029] Step S2, Chelating Adsorption and Enrichment: After complex breaking, the wastewater sequentially enters a two-stage series adsorption tower at a flow rate of 2 BV / h, with macroporous aminophosphonic acid chelating resin packed inside. Continuous adsorption treatment is performed, and the total copper ion concentration in the two-stage effluent stabilizes at 0.05 mg / L. After the resin becomes saturated, it is regenerated countercurrently for 40 min with a 12% (w / w) dilute hydrochloric acid solution at a flow rate of 1.2 BV / h. The enriched solution is collected, where the copper ion concentration reaches 36 g / L.

[0030] Step S3, Low-pressure electrolysis: The enriched solution is pumped into the electrolytic cell. The anode is a titanium-based ruthenium-iridium alloy mesh, and the cathode is a 316L stainless steel plate. Electrolysis is carried out for 5 hours at an electrolysis temperature of 35℃, a voltage of 1.5V, and a current density of 100A / ㎡. Bright copper sheets are deposited on the cathode. After peeling, washing, drying, and weighing, the purity is calculated to be 99.62%, meeting the requirements for electronic-grade copper. After electrolysis, the copper concentration in the tail liquid drops to 3.2g / L. This tail liquid is entirely returned to the regeneration process, mixed with fresh hydrochloric acid, and used for resin regeneration.

[0031] Step S4, Deep purification and reuse: The adsorbed water enters the granular coconut shell activated carbon tower for adsorption, with a contact time of 20 minutes, and then passes through a 5μm precision security filter.

[0032] The final effluent quality is: copper ions 0.03mg / L, COD 28mg / L, conductivity 165μS / cm, which meets the standards for circuit board surface cleaning water and can be directly reused, with a daily reuse rate of 80%.

[0033] Step S5, tail liquid full recycling treatment: The small amount of tail liquid generated by activated carbon backwashing is treated by cation exchange resin column, and the copper ion in the effluent is <0.05mg / L. All of it is reused for the next batch of backwashing or workshop floor cleaning, and there is no wastewater discharge.

[0034] Example 2

[0035] The wastewater had a copper ion concentration of 800 mg / L and a high proportion of complexed ions, which was treated using this method. In step S1, the high-efficiency composite complex-breaking agent formula was adjusted to: 18% sodium persulfate, 10% polyferric sulfate, 4% sodium gluconate, and the remainder water; the dosage was 3%, the pH was adjusted to 5.5, and the reaction time was 35 min. In step S2, the adsorption flow rate was 1.5 BV / h, the regeneration hydrochloric acid concentration was 15%, and the regeneration time was 45 min, resulting in a enriched solution with a copper concentration of 38 g / L. In step S3, the electrolysis voltage was 1.8 V, the current density was 110 A / m², the temperature was 40℃, and the electrolysis time was 6 h, yielding electrolytic copper with a purity of 99.51%. In step S4, the effluent had a copper concentration of 0.08 mg / L, a COD of 42 mg / L, and a conductivity of 190 μS / cm, all meeting standards for reuse. The system operated stably and also achieved zero discharge.

[0036] As can be seen from the above embodiments, the method of the present invention exhibits excellent effects in breaking down complexes, enriching and electrolytically recovering copper-containing wastewater from circuit boards of different concentrations, with no external discharge, and possesses the functions of high-purity copper resource recovery and water resource recycling, thus having high application value.

[0037] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for copper recovery from low-concentration copper-containing wastewater from circuit boards, characterized in that, include: Step S1, pretreatment and complex breaking treatment of copper-containing wastewater: filter the copper-containing wastewater to remove impurities, add complex breaking agent and stir to react, so that the complexed copper in the wastewater is converted into free copper ions. Step S2, chelation adsorption enrichment: The wastewater treated in step S1 is adsorbed through an adsorption unit filled with chelating resin, so that copper ions are selectively adsorbed and the copper ion concentration in the effluent is ≤0.1mg / L; when the chelating resin is saturated, it is regenerated using a dilute acid solution as a regenerator to obtain a high-concentration copper salt enriched solution. Step S3, electrolytic recovery of copper: The high-concentration copper salt enrichment solution is electrolyzed, and electrolytic copper is deposited at the cathode. The tail liquid after electrolysis is returned to step S2 for recycling. Step S4, Deep purification and reuse: The adsorbed water from step S2 is purified and reused in the production process after being adsorbed by activated carbon and filtered by precision. Step S5, tail liquid treatment: The system tail liquid is treated with ion exchange resin and then reused to achieve zero wastewater discharge.

2. The method for copper recovery from low-concentration copper-containing wastewater from circuit boards according to claim 1, characterized in that, The complex-breaking agent mentioned in step S1 is a composite complex-breaking agent, whose components, by mass percentage, include: 12%–18% sodium persulfate, 6%–10% polyferric sulfate, 4%–6% sodium gluconate, and the balance being deionized water.

3. The method for copper recovery from low-concentration copper-containing wastewater from circuit boards according to claim 1, characterized in that, The dosage of the composite complex-breaking agent in step S1 is 1.5% to 3% of the total mass of wastewater; the stirring reaction conditions are: normal temperature and pressure, stirring speed of 250 to 350 r / min, reaction time of 25 to 35 min, and the pH value of the wastewater is adjusted to 5.0 to 6.

5.

4. The method for copper recovery from low-concentration copper-containing wastewater from circuit boards according to claim 1, characterized in that, The adsorption unit in step S2 is a two-stage chelating resin adsorption tower connected in series, wherein the chelating resin is a macroporous aminophosphonic acid chelating resin; the wastewater flow rate through the tower during adsorption is 1.5-3 BV / h, and the process is carried out at room temperature; the dilute acid solution used for regeneration is dilute hydrochloric acid with a mass concentration of 10%-15%, the regeneration flow rate is 1-1.5 BV / h, countercurrent regeneration is adopted, and the regeneration time is 30-45 min, resulting in a high-concentration copper chloride enriched solution with a copper ion concentration of 30-40 g / L.

5. The method for copper recovery from low-concentration copper-containing wastewater from circuit boards according to claim 1, characterized in that, In step S3, the anode used for electrolysis is a titanium-based ruthenium-iridium alloy anode, and the cathode is a 316L stainless steel plate. The electrolysis process parameters are: electrolysis temperature 30-40℃, electrolysis voltage 1.2-1.8V, current density 80-110A / ㎡, and electrolysis time 4-6h. The purity of the obtained electrolytic copper is ≥99.5%. The copper ion concentration in the tail liquid after electrolysis is reduced to 2-4g / L.

6. The method for copper recovery from low-concentration copper-containing wastewater from circuit boards according to claim 1, characterized in that, In step S4, granular coconut shell activated carbon is used for activated carbon adsorption, and the filtration accuracy of precision filtration is 5μm. The water quality indicators of the resulting purified reclaimed water are: copper ions ≤0.1mg / L, COD ≤50mg / L, conductivity ≤200μS / cm, which can be reused in circuit board surface cleaning, acid washing, or cooling cycle processes.

7. The method for copper recovery from low-concentration copper-containing wastewater from circuit boards according to claim 1, characterized in that, The ion exchange resin mentioned in step S5 is a cation exchange resin, and the treated tail liquid is reused for activated carbon backwashing or production cleaning.

8. The method for copper recovery from low-concentration copper-containing wastewater from circuit boards according to claim 1, characterized in that, In step S1, the copper ion concentration in the copper-containing wastewater is 50 mg / L to 1 g / L.

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