A method for low-temperature evaporation drying crystallization and deep electrolysis of low-copper-containing waste liquid

Abstract

The present application relates to a kind of low copper-containing waste liquid low-temperature evaporation drying crystallization depth electrolytic copper method, belong to industrial waste liquid resource processing technical field.The method is aimed at circuit board industry brownification-copper mixed waste liquid, sequentially carries out pretreatment, gradient negative pressure evaporation concentration, crystallization drying purification, adaptability pulse electrolysis and full-process recycling post-processing.By evaporation concentration, no chemical reagent is achieved, and low organic residue crystal is obtained by crystallization purification, and depth electrolysis is carried out using customized pulse electrolysis parameters and additives.The present application replaces traditional chemical breakage, avoids secondary pollution, and realizes efficient recovery of copper resources.The purity of final electrolytic copper is ≥99.95%, the total recovery rate of copper is ≥96.8%, the energy consumption per ton of copper is significantly reduced, the production of hazardous waste containing copper is reduced by more than 95%, the condensate reuse rate is ≥80%, and excellent environmental and economic benefits are achieved.

Description

Technical Field

[0001] This invention relates to the field of industrial waste liquid resource utilization technology, specifically to a method for deep electrolytic copper extraction from low-copper-content waste liquid through low-temperature evaporation, drying, crystallization. Background Technology

[0002] With the rapid development of the electronics and metal processing industries, the amount of copper-containing wastewater generated is increasing year by year. Copper-containing wastewater mainly originates from processes such as printed circuit board etching, electroplating rinsing, and metal surface treatment, and contains copper ions, complexing agents, organic additives, and small amounts of heavy metals. Improper disposal not only wastes copper resources but also causes serious environmental pollution. Therefore, the resource-based treatment of copper-containing wastewater has become a key focus of the industry.

[0003] Currently, the main methods for treating copper-containing wastewater include chemical precipitation, ion exchange, membrane separation, and electrolysis. Among these: Chemical precipitation is the most widely used treatment method, which involves adding alkaline solutions or sulfides to cause copper ions to form precipitates. However, this method has the following problems: (1) It generates a large amount of copper-containing sludge, which is hazardous waste and has high disposal costs; (2) For complexed copper, it is necessary to break the complex first, which usually requires the addition of oxidants or chelating agents, increasing the cost of reagents; (3) The copper resources are recovered in the form of sludge, which has a low grade and requires further smelting before it can be utilized.

[0004] Ion exchange and membrane separation methods can achieve copper enrichment and recovery, but they have the following drawbacks: (1) Resins and membranes are easily contaminated by organic matter and have a short service life; (2) They are not adaptable to waste liquids with high salt content and high organic matter content; (3) They have high operating and maintenance costs and are difficult to apply on a large scale.

[0005] Traditional electrolysis can directly recover electrolytic copper from waste liquid, but it has obvious limitations for low copper content waste liquid (copper concentration <5g / L): (1) low current efficiency and high energy consumption; (2) low grade of deposited copper and high impurity content; (3) the electrolyte needs to be continuously replenished with new liquid, and closed-loop circulation cannot be achieved.

[0006] Evaporation concentration can reduce the volume of waste liquid, but traditional evaporation processes have the following problems: (1) high evaporation temperature (usually >100℃) and high energy consumption; (2) the complex bond is stable under high temperature conditions, and additional complex-breaking agents need to be added; (3) the evaporation condensate has poor water quality and is difficult to reuse; (4) the crystallization product has high impurity content, which affects the quality of subsequent electrolysis.

[0007] In addition, existing copper-containing wastewater treatment technologies generally suffer from the following common problems: Low copper recovery rate: Most technologies have a copper recovery rate of less than 90%, with a large amount of copper being lost in waste residue or wastewater; Large volume of hazardous waste: The treatment process generates copper-containing sludge or residue, increasing the cost of secondary disposal. Water waste: The treated water is difficult to meet the standards for reuse, and water resource recycling cannot be achieved; The process chain is fragmented: concentration, crystallization, electrolysis and other processes operate independently, and materials cannot be utilized in a closed loop.

[0008] Therefore, developing a comprehensive treatment technology that can achieve efficient reduction of low-copper-content waste liquid, high-grade recovery of copper resources, no hazardous waste generation during the treatment process, and recycling of water resources has become an urgent need in the field of copper-containing waste liquid treatment. Summary of the Invention

[0009] To address the aforementioned problems in existing technologies, this invention provides a method for deep electrolytic copper extraction from low-copper-content waste liquid through low-temperature evaporation, drying, crystallization, and treatment. This method primarily solves the following technical problems: existing copper-containing waste liquid treatment technologies have low copper recovery rates, with some copper resources lost along with waste residue or wastewater; traditional chemical precipitation methods generate large amounts of hazardous waste such as copper-containing sludge, resulting in high secondary disposal costs; treatment of complexed copper requires the addition of chemical agents to break the complex, increasing treatment costs and potentially introducing new pollutants; traditional evaporation processes involve high temperatures and energy consumption, and the evaporation condensate has poor water quality, making reuse difficult; direct electrolysis of low-copper-content waste liquid results in low current efficiency and unsatisfactory copper grade; and the various stages of the treatment process are relatively independent, making closed-loop material utilization difficult and water resource utilization low.

[0010] A method for deep electrolytic copper extraction from low-copper-content waste liquid through low-temperature evaporation, drying, crystallization, and other steps includes the following steps: Step 1: Pretreatment: Add ferrous agent to copper-containing waste liquid to remove hydrogen peroxide, filter after aeration, and adjust the pH to 3-5 to obtain pretreated liquid. Step 2, Evaporation and Concentration: The pretreated liquid is concentrated using a two-stage gradient negative pressure evaporation process to obtain a copper-containing concentrate; the two-stage gradient negative pressure evaporation process includes a front-stage low-temperature high negative pressure evaporation and a rear-stage medium-temperature negative pressure evaporation. Step 3, Crystallization and Drying: The concentrated solution is centrifuged to obtain crude crystals, which are then washed and dried under low temperature and negative pressure to obtain purified crystals; Step 4, Pulse Electrolysis: The purified crystals are prepared into an electrolyte solution, and after adding composite additives, pulse electrolysis is performed to obtain electrolytic copper at the cathode. Step 5, Post-recycling treatment: The electrolyte after electrolysis is returned to the crystallization and dissolution stage for recycling, and the evaporated condensate is reused in the production line.

[0011] Furthermore, in the pretreatment step: the ferrous agent is ferrous sulfate or ferrous chloride, the dosage is 1.5-2.5 kg / t waste liquid, and the reaction is stirred for 30-60 min; compressed air aeration is performed for 18-30 h, with an aeration intensity of 0.6-1.0 m³ / (m²・h); and 3-8 μm precision filtration is used to remove suspended solids.

[0012] Furthermore, the evaporation and concentration step adopts a two-stage gradient negative pressure evaporation process: the first stage evaporation temperature is 45-50℃ and the vacuum degree is -95 to -96KPa, evaporating until the waste liquid volume is reduced by 60% to 70%; the second stage evaporation temperature is 70-80℃ and the vacuum degree is -85 to -96KPa.

[0013] Furthermore, the concentration ratio of the evaporation and concentration step is ≥90%, resulting in a concentrated solution containing 50-80 g / L of copper.

[0014] Furthermore, in the crystallization and drying step: the centrifugation speed is 2500-3000 r / min, and the time is 10-15 min; the crystals are washed with distilled water or deionized water, with a liquid-to-solid ratio of 1:0.3-0.7, and the stirring and washing is carried out for 15-20 min; the low-temperature drying temperature is 60-80℃, the vacuum degree is -0.08 to -0.1 MPa, and the drying time is 2-3 h.

[0015] Furthermore, the electrolyte in the pulse electrolysis step is prepared with 20-30 g / L copper and 100-150 g / L sulfuric acid; the composite additive is 0.05-0.1 g / L gelatin and 0.02-0.05 g / L thiourea.

[0016] Furthermore, the electrolysis parameters for the pulse electrolysis step are: current density 200-300 A / m², pulse frequency 10-50 Hz, duty cycle 50%-70%, cell voltage 1.7-2.1 V, electrolyte temperature 30-40 °C, and electrolysis time 48-72 h.

[0017] Furthermore, in the pulse electrolysis step: when the copper concentration in the electrolyte drops to 5-10 g / L, electrolysis is stopped, and the electrolyte is returned to the crystallization and dissolution stage to prepare a new electrolyte.

[0018] Furthermore, in the post-processing step of the cycle: the evaporated condensate is filtered through a 5μm filter and then reused in the production line.

[0019] Furthermore, in the post-processing step, all the electrolyte after electrolysis is returned to the crystallization and dissolution stage for recycling.

[0020] Compared with existing technologies, this invention has the following advantages: This invention enriches copper in waste liquid to 50-80 g / L through evaporation and concentration, followed by deep recovery via pulse electrolysis. The total copper recovery rate of the entire process can reach over 96.8%. The electrolyzed liquid is recycled, effectively reducing copper resource loss with waste liquid. This invention uses electrolysis to directly recover metallic copper. Compared with traditional chemical precipitation methods, according to comparative data from examples, the yield of copper-containing hazardous waste can be reduced by over 95%, helping to reduce secondary disposal costs and environmental risks. This invention employs a two-stage gradient negative pressure evaporation process. Under high concentrations of sulfate and sodium ions, the complexing agent competes for the binding sites of copper ions, promoting the breakage of complex bonds. According to data from examples, no additional oxidants or chelating agents are needed to break the complex, reducing reagent costs. This invention uses low-temperature negative pressure evaporation, with the initial temperature at 45-50℃ and the subsequent temperature at 70-80℃. Compared to traditional evaporation processes (typically >100℃), energy consumption can be reduced by 30%–40% according to energy consumption test data from the embodiments. Simultaneously, the negative pressure condition facilitates the removal of volatile organic compounds. Organic matter and impurities are removed through a crystallization and drying step, followed by pulse electrolysis with the addition of composite additives (gelatin and thiourea), resulting in fine and uniform copper crystals. According to test data from the embodiments, the purity of electrolyzed copper can reach over 99.95%. The evaporation condensate, after 5μm filtration, meets reuse standards. According to water quality test data from the embodiments, the reuse rate can reach over 80%, helping to reduce the amount of fresh water replenishment. This invention enables a circular mode where the electrolyzed liquid is returned to the crystallization and dissolution stage, and the evaporation condensate is reused in the production line, facilitating full utilization of materials and reducing wastewater discharge. This invention can treat low-copper-content wastewater with a copper concentration of 0.5–5 g / L, as well as wastewater containing complexing agents and organic additives, with relatively stable process operation. Attached Figure Description

[0021] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0022] The present invention will be further described in detail below with reference to embodiments. It should be understood that these descriptions are intended to enable those skilled in the art to reproduce and implement the present invention, and are not intended to limit the scope of protection of the present invention.

[0023] This invention relates to a method for deep electrolytic copper extraction from low-copper-content waste liquid through low-temperature evaporation, drying, crystallization, and treatment. It belongs to the field of industrial waste liquid resource utilization technology and is particularly suitable for treating browning-copper mixed waste liquid generated during PCB manufacturing. This method aims to solve the problems of incomplete chemical complex breaking, low copper recovery grade, high energy consumption, serious secondary pollution, and large hazardous waste production in existing technologies.

[0024] Example 1 This embodiment provides a complete processing flow, demonstrating the implementation and beneficial effects of the present invention with specific parameters and results.

[0025] 1380 kg of mixed waste liquid containing browning and copper plating from the PCB production line was collected. Testing revealed that the waste liquid had a COD of 12000 mg / L, a pH of 1.8, contained 3.2 g / L of copper, 0.8 g / L of nickel, and 0.3% of hydrogen peroxide.

[0026] 2.76 kg of ferrous sulfate heptahydrate was added to the above waste liquid, and the mixture was reacted for 45 min with stirring, followed by aeration at an intensity of 0.8 m³ / (m²·h) for 24 h. After aeration, the solution was filtered through a 5 μm fine filter, and the pH was adjusted to 4.0 with dilute sulfuric acid to obtain a pretreated solution. The pretreated solution was then passed into a low-temperature evaporation system for two-stage gradient negative pressure evaporation: the first stage was controlled at a temperature of 48°C and a vacuum of -95 kPa, evaporating until the volume reduction was 65%; the second stage was controlled at a temperature of 75°C and a vacuum of -90 kPa, continuing evaporation until the total concentration ratio reached 91%. The concentrated solution was centrifuged at 2800 r / min to obtain wet-based crude copper sulfate crystals.

[0027] 48.5 kg of distilled water (liquid-to-solid ratio 1:0.5) was added to the coarse crystals and washed for 18 min. The crystals were then dried at 70°C and -0.09 MPa for 2.5 h to obtain 82 kg of purified crystals (8% water content, 0.08% nickel content). The purified crystals were dissolved in dilute sulfuric acid to prepare a 500 L electrolyte containing 25 g / L copper, 120 g / L sulfuric acid, and 0.08 g / L gelatin and 0.03 g / L thiourea. The electrolyte was injected into a single-chamber electrolytic cell and electrolyzed for 48 h at a current density of 250 A / m², a pulse frequency of 30 Hz, and a duty cycle of 60%, with the cell voltage controlled at 1.9 V and the liquid temperature at 35°C.

[0028] After electrolysis, the cathode plate is removed, rinsed, and dried to obtain the electrolytic copper product. Testing showed that the electrolytic copper purity was 99.96%, the overall copper recovery rate was 97.2%, the current efficiency was 86%, and the energy consumption per ton of copper was 1480 kWh. The electrolytic liquid (containing 8 g / L of copper) is returned to dissolve the next batch of purified crystals; the condensate generated from evaporation, after passing testing, is reused in the production line.

[0029] Example 2 1600 kg of mixed waste liquid containing browning and copper plating from the PCB production line was collected. Testing revealed that the waste liquid had a COD of 15000 mg / L, a pH of 2.5, contained 2.0 g / L of copper, and 0.2% hydrogen peroxide.

[0030] 3.2 kg of ferrous sulfate was added to the above waste liquid, and the mixture was reacted for 60 min with stirring, followed by aeration at an intensity of 1.0 m³ / (m²·h) for 30 h. After aeration, the solution was filtered through a 3 μm fine filter, and the pH was adjusted to 3.5 with dilute sulfuric acid to obtain a pretreated solution. The pretreated solution was then passed into a low-temperature evaporation system for two-stage gradient negative pressure evaporation: the first stage controlled the temperature at 50°C and the vacuum at -96 kPa, evaporating until the volume reduction was 70%; the second stage controlled the temperature at 80°C and the vacuum at -96 kPa, continuing evaporation until the total concentration ratio reached 92%. The concentrated solution was centrifuged at 3000 r / min to obtain wet-based crude copper sulfate crystals.

[0031] The coarse crystals were washed with deionized water (liquid-to-solid ratio 1:0.7) for 20 min, and then dried at 80°C and -0.1 MPa for 3 h to obtain purified crystals (7.5% water content). The purified crystals were dissolved in dilute sulfuric acid to prepare a 600 L electrolyte containing 22 g / L copper, 110 g / L sulfuric acid, and 0.05 g / L gelatin and 0.02 g / L thiourea. The electrolyte was injected into a single-chamber electrolytic cell and electrolyzed for 72 h at a current density of 200 A / m², a pulse frequency of 10 Hz, and a duty cycle of 50%, with the cell voltage controlled at 1.7 V and the liquid temperature at 30°C.

[0032] After electrolysis, the cathode plate is removed, rinsed, and dried to obtain the electrolytic copper product. Testing showed that the electrolytic copper purity was 99.95%, the overall copper recovery rate was 96.8%, the current efficiency was 84%, and the energy consumption per ton of copper was 1550 kWh. The electrolytic liquid (containing 7 g / L of copper) is returned to dissolve the next batch of purified crystals; the condensate generated from evaporation, after passing testing, is reused in the production line.

[0033] Example 3 1200 kg of mixed waste liquid containing browning and copper plating from the PCB production line was collected. Testing revealed that the waste liquid had a COD of 9000 mg / L, a pH of 1.5, contained 4.5 g / L of copper, and 0.4% hydrogen peroxide.

[0034] 1.8 kg of ferrous chloride was added to the above waste liquid, and the mixture was reacted for 30 min with stirring, followed by aeration at an intensity of 0.6 m³ / (m²·h) for 18 h. After aeration, the solution was filtered through an 8 μm fine filter, and the pH was adjusted to 5.0 with dilute sulfuric acid to obtain a pretreated solution. The pretreated solution was then passed into a low-temperature evaporation system for two-stage gradient negative pressure evaporation: the first stage controlled the temperature at 45°C and the vacuum at -95 kPa, evaporating until the volume reduction was 60%; the second stage controlled the temperature at 70°C and the vacuum at -85 kPa, continuing evaporation until the total concentration ratio reached 93%. The concentrated solution was centrifuged at 2500 r / min to obtain wet-based crude copper sulfate crystals.

[0035] Distilled water (liquid-to-solid ratio 1:0.3) was added to the coarse crystals and washed for 15 min, followed by drying at 60°C and -0.08 MPa for 2 h to obtain purified crystals (water content 9.0%). The purified crystals were dissolved in dilute sulfuric acid to prepare a 450 L electrolyte containing 30 g / L copper, 150 g / L sulfuric acid, and 0.1 g / L gelatin and 0.05 g / L thiourea. The electrolyte was injected into a single-chamber electrolytic cell and electrolyzed for 48 h at a current density of 300 A / m², a pulse frequency of 50 Hz, and a duty cycle of 70%, with the cell voltage controlled at 2.1 V and the liquid temperature at 40°C.

[0036] After electrolysis, the cathode plate is removed, rinsed, and dried to obtain the electrolytic copper product. Testing showed that the electrolytic copper purity was 99.98%, the overall copper recovery rate was 97.5%, the current efficiency was 89%, and the energy consumption per ton of copper was 1420 kWh. The electrolyte (containing 6 g / L of copper) is returned to dissolve the next batch of purified crystals; the condensate generated from evaporation, after passing testing, is reused in the production line.

[0037] Implementation effect Product quality: The final electrolytic copper product has a purity of 99.96%, which meets the requirements for high-purity copper in GB / T467-2010 standard and has high economic value.

[0038] Resource recovery efficiency: The total copper recovery rate of the entire process reaches 97.2%. The current efficiency of the electrolysis section is as high as 86%, indicating that electrical energy is used efficiently.

[0039] Energy consumption: The total power consumption for producing one ton of electrolytic copper is 1480 kWh, which is significantly lower than that of traditional electrolysis processes.

[0040] Environmental benefits: The entire process eliminates the need for chemical complex-breaking agents such as sodium sulfide and sodium hypochlorite, thus preventing secondary pollution at the source, including hydrogen sulfide emissions, increased COD, and the introduction of impurity ions. The amount of copper-containing hazardous solid waste generated by the process is reduced by more than 95% compared to traditional neutralization and precipitation methods. The vast majority of copper resources are recovered as high-purity products, and a high proportion of condensate is reused.

Claims

1. A method for deep electrolytic copper extraction from low-copper-content waste liquid through low-temperature evaporation, drying, crystallization, and electrolysis, characterized in that... Includes the following steps: Pretreatment steps: Add ferrous agent to copper-containing waste liquid to remove hydrogen peroxide, filter after aeration, adjust pH to 3-5 to obtain pretreated liquid; Evaporation and concentration steps: The pretreated liquid is concentrated using a two-stage gradient negative pressure evaporation process to obtain a copper-containing concentrate; Crystallization and drying steps: The concentrate is centrifuged to obtain coarse crystals, which are then washed and dried under low temperature and negative pressure to obtain purified crystals; Pulse electrolysis steps: The purified crystals are prepared into an electrolyte solution, and after adding composite additives, pulse electrolysis is performed to obtain electrolytic copper at the cathode; Post-recycling processing steps: The electrolyte after electrolysis is returned to the crystallization and dissolution stage for recycling, and the evaporated condensate is reused in the production line.

2. The method for low-temperature evaporation, drying, crystallization, and deep electrolytic copper extraction from low-copper-content waste liquid according to claim 1, characterized in that, In the pretreatment step: the dosage of ferrous agent is 1.5-2.5 kg / t of waste liquid, and the reaction is stirred for 30-60 min; compressed air aeration is carried out for 18-30 h with an aeration intensity of 0.6-1.0 m³ / (m²・h); and 3-8 μm precision filtration is used to remove suspended solids.

3. The method for low-temperature evaporation, drying, crystallization, and deep electrolytic copper extraction from low-copper-content waste liquid according to claim 1, characterized in that, The evaporation and concentration step adopts a two-stage gradient negative pressure evaporation process: the first stage temperature is 45-50℃ and the negative pressure is -95 to -96Kpa, evaporating until the waste liquid volume is reduced by 60% to 70%; the second stage temperature is 70-80℃ and the negative pressure is -85 to -96Kpa.

4. The method for low-temperature evaporation, drying, crystallization, and deep electrolytic copper extraction from low-copper-content waste liquid according to claim 1, characterized in that, The concentration ratio of the evaporation and concentration step is ≥90%, resulting in a concentrated solution containing 50-80 g / L of copper.

5. The method for low-temperature evaporation, drying, crystallization, and deep electrolytic copper extraction from low-copper-content waste liquid according to claim 1, characterized in that, In the crystallization drying step: the centrifugation speed is 2500-3000 r / min, and the time is 10-15 min; The crystals were washed with distilled water at a liquid-to-solid ratio of 1:0.3 to 0.7, and stirred for 15 to 20 minutes. The low-temperature drying temperature was 60 to 80℃, the negative pressure was -0.08 to -0.1 MPa, and the drying time was 2 to 3 hours.

6. The method for low-temperature evaporation, drying, crystallization, and deep electrolytic copper extraction from low-copper-content waste liquid according to claim 1, characterized in that, The electrolyte in the pulse electrolysis step is prepared with 20-30 g / L copper and 100-150 g / L sulfuric acid; the composite additive is 0.05-0.1 g / L gelatin and 0.02-0.05 g / L thiourea.

7. The method for low-temperature evaporation, drying, crystallization, and deep electrolytic copper extraction from low-copper-content waste liquid according to claim 1, characterized in that, The electrolysis parameters for the pulse electrolysis step are: current density 200-300 A / m², pulse frequency 10-50 Hz, duty cycle 50%-70%, cell voltage 1.7-2.1 V, electrolyte temperature 30-40 °C, and electrolysis time 48-72 h.

8. The method for low-temperature evaporation, drying, crystallization, and deep electrolytic copper extraction from low-copper-content waste liquid according to claim 1, characterized in that, In the pulse electrolysis step: when the copper concentration in the electrolyte drops to 5-10 g / L, electrolysis is stopped, and the electrolyte is returned to the crystallization and dissolution step to prepare a new electrolyte.

9. The method for low-temperature evaporation, drying, crystallization, and deep electrolytic copper extraction from low-copper-content waste liquid according to claim 1, characterized in that, In the post-processing step of the cycle: the evaporated condensate is filtered through a 5μm filter and then reused in the production line.

10. The method for low-temperature evaporation, drying, crystallization, and deep electrolytic copper extraction from low-copper-content waste liquid according to claim 1, characterized in that, In the post-processing step, all electrolyte is returned to the crystallization and dissolution stage for recycling, thus achieving closed-loop utilization of the electrolyte.

Images