A method for stepwise recovery of gold and copper from waste printed circuit boards

Abstract

The application provides a method for step-by-step recovery of gold and copper from waste printed circuit boards, comprising flotation, electro-oxidation leaching and synchronous electro-deposition recovery of copper and electro-oxidation leaching and synchronous electro-deposition recovery of gold. The application adopts flotation technology to separate plastics and metals, adopts electro-oxidation leaching and synchronous electro-deposition technology to leach and electro-deposit copper and gold respectively, and step-by-step extraction to obtain metal copper and gold. The method can realize efficient separation and recovery of gold and copper, reduce subsequent separation processes and costs, realize resource utilization of waste printed circuit boards, and has wide industrial application prospect. The application adopts electro-oxidation leaching and synchronous electro-deposition recovery of copper technology, and the electrolyte contains CuSO4, NH3H2O, (NH4)2SO4 and ethylenediamine. By adding ethylenediamine in the electrolyte, the use amount of ammonia water can be reduced, and the copper recovery rate can be accelerated. The cathode copper-clad plate with smooth and dense surface can be obtained at low current density, and the recovery rate of copper reaches more than 90%, and the purity reaches more than 90%.

Description

Technical Field

[0001] This invention relates to the field of metal recycling technology, and in particular to a method for the stepwise recovery of gold and copper from waste printed circuit boards. Background Technology

[0002] Over the past 20 years, electronic products such as computers, mobile phones, home appliances, and instruments have developed rapidly, bringing convenience to people's lives and work while also generating a large amount of electronic waste. Printed circuit boards (PCBs) are composed of a substrate made of resin and fiberglass materials, copper rivets and metal foil on the substrate, and electronic components. Waste PCBs mainly contain precious metals such as gold, silver, and palladium, as well as heavy and light metals such as copper, aluminum, zinc, iron, and nickel. The copper content is as high as 13% or more, and the gold content is over 40g / t, which is far higher than the grade of ore.

[0003] Technologies for recovering metals, particularly copper and gold, from waste printed circuit boards (PCBs) can be categorized into mechanical physical methods, pyrometallurgical methods, biochemical methods, hydrometallurgical methods, and electrolytic technologies. However, mechanical methods typically yield a mixture of metals and non-metals; pyrometallurgical processes are generally energy-intensive; biometallurgical methods have long processing cycles; and hydrometallurgical processes involve large amounts of leaching agents. In contrast, electrolytic technology is considered an economical and effective method for recovering metals from waste PCBs.

[0004] However, the metal extraction rate of traditional electrolysis methods is still relatively low. Therefore, it is of great significance to develop environmentally friendly and efficient stepwise recovery methods for gold and copper, improve the metal extraction rate from waste printed circuit boards, and maximize the acquisition of usable components. Summary of the Invention

[0005] Based on this, the present invention provides a method for stepwise recovery of gold and copper from waste printed circuit boards with a high metal extraction rate.

[0006] A method for stepwise recovery of gold and copper from waste printed circuit boards includes flotation, electro-oxidation leaching with simultaneous electrowinning to recover copper, and electro-oxidation leaching with simultaneous electrowinning to recover gold.

[0007] The flotation step specifically includes: crushing waste printed circuit boards to a particle size of less than 0.425mm, then mixing them with water and a wetting agent for flotation to obtain foam products and in-tank products; the foam products are products enriched with plastics, and the in-tank products are products enriched with gold and copper;

[0008] The specific steps of the electro-oxidation leaching and simultaneous electrowinning copper recovery process include: placing the product in the tank into an electrolytic cell, performing electro-oxidation leaching with a copper ammonia alkaline electrolyte, and simultaneously recovering copper by electrowinning to obtain leaching residue and electrowinning copper; the copper ammonia alkaline electrolyte contains CuSO4, (NH4)2SO4, NH3·H2O and ethylenediamine;

[0009] When the electro-oxidation leaching and simultaneous electrowinning gold recovery step is performed after the electro-oxidation leaching and simultaneous electrowinning copper recovery step, it specifically includes: placing the leaching residue obtained from the electro-oxidation leaching and simultaneous electrowinning copper recovery step into an electrolytic cell, performing electro-oxidation leaching with potassium iodide electrolyte, and simultaneously recovering gold by electrowinning.

[0010] When the electro-oxidation leaching and simultaneous electrowinning gold recovery step is performed before the flotation step, it specifically includes: using waste printed circuit boards as anodes, electro-oxidation leaching of gold is carried out in a thiourea-sodium chloride-chloroaurate electrolyte, while simultaneously recovering gold by electrowinning. Within the same electrowinning cycle, the waste printed circuit boards with the anode are replaced at least 10 times, so that gold is enriched at the cathode.

[0011] In other words, by adjusting the timing and conditions of the simultaneous electro-oxidation leaching and electrowinning step for gold recovery, two process flows can be formed. Scheme 1 is flotation – simultaneous electro-oxidation leaching and electrowinning for copper recovery – simultaneous electro-oxidation leaching and electrowinning for gold recovery:

[0012] SA1 flotation: Waste printed circuit boards are crushed to a particle size of less than 0.425mm, then mixed with water and wetting agent for flotation to obtain foam products and products in the tank;

[0013] SA2 Electro-oxidative leaching with simultaneous electrowinning to recover copper: The product obtained in step SA1 is placed in an electrolytic cell and electro-oxidatively leached with copper ammonia alkaline electrolyte, while copper is simultaneously recovered by electrowinning, resulting in leaching residue and electrowinning copper.

[0014] SA3 Electro-oxidative leaching with simultaneous electrowinning for gold recovery: The leaching residue obtained in step SA2 is placed in an electrolytic cell and electro-oxidative leaching is performed with potassium iodide electrolyte, while gold is recovered by electrowinning.

[0015] Option 2 involves simultaneous electro-oxidation leaching and electrowinning for gold recovery, followed by flotation and simultaneous electro-oxidation leaching and electrowinning for copper recovery.

[0016] SB1 Electro-oxidation Leaching Simultaneous Electrodeposition for Gold Recovery: Using waste printed circuit boards as the anode, gold is electro-oxidized and leached in a thiourea-sodium chloride-chloroaurate electrolyte, while gold is simultaneously recovered by electrodeposition. Within the same electrodeposition cycle, the waste printed circuit boards with the anode are replaced at least 10 times to enrich gold at the cathode.

[0017] SB2 flotation: The waste printed circuit boards processed in step SB1 are crushed to a particle size of less than 0.425mm, and then mixed with water and wetting agent for flotation to obtain foam products and products in the tank;

[0018] SB3 Electro-oxidation Leaching with Simultaneous Electrowinning to Recover Copper: The product obtained in step SB2 is placed in an electrolytic cell and electro-oxidized with a copper-ammonia alkaline electrolyte, while copper is recovered by electrowinning.

[0019] In one embodiment, the concentration of CuSO4 in the copper ammonia alkaline electrolyte is 0.05–0.3 mol / L; preferably, the concentration of (NH4)2SO4 is 0.1–0.3 mol / L; preferably, the concentration of NH3·H2O is 0.1–0.3 mol / L; preferably, the concentration of ethylenediamine is 0.1–0.6 mol / L.

[0020] In one embodiment, during the electro-oxidation leaching and simultaneous electrowinning copper recovery step, the current density is 10–30 mA / cm². 2 Preferably, the electrolysis time is 3 to 7 hours, and preferably, the solid-liquid ratio, i.e., the mass-volume ratio of the product in the tank (calculated on a dry basis) to the electrolyte, is 10 to 40 g / L.

[0021] In one embodiment, in the electro-oxidation leaching and simultaneous electrowinning copper recovery step, the anode is selected from any one of DSA, graphite and titanium mesh, and the cathode is a titanium plate.

[0022] In one embodiment, when the electro-oxidation leaching and simultaneous electrowinning for gold recovery step is performed after the electro-oxidation leaching and simultaneous electrowinning for copper recovery step, the concentration of potassium iodide in the potassium iodide electrolyte is 5-30 g / L; preferably, the electrolysis voltage is 2-6 V; preferably, the electrolysis time is 0.5-3 h; preferably, the solid-liquid ratio, i.e., the mass-volume ratio of the leaching residue (calculated on a dry basis) to the electrolyte, is 100-200 g / L.

[0023] In one embodiment, when the electro-oxidation leaching simultaneous electrowinning gold recovery step is performed after the electro-oxidation leaching simultaneous electrowinning copper recovery step, the anode is selected from any one of DSA, graphite, and titanium mesh, and the cathode is selected from any one of graphite, titanium mesh, and carbon fiber.

[0024] In one embodiment, when the electro-oxidation leaching and simultaneous electrowinning gold recovery step is performed before the flotation step, the thiourea-sodium chloride-chloroaurate electrolyte contains 0.5 wt% to 4 wt% thiourea; preferably, the sodium chloride content is 0.5 wt% to 4 wt%; preferably, the chloroaurate concentration is 30 to 40 mg / L; preferably, the cathode is selected from any one of graphite, titanium mesh, and carbon fiber, and the distance between the anode and the cathode is 3 to 10 cm; preferably, the electrolysis voltage is 1.5 to 4 V; preferably, the electrolysis time for each waste printed circuit board is 5 s to 18 min.

[0025] In one embodiment, the chloroaurate ion is derived from any one or more of tetrachloroauric acid, sodium chloroaurate, or potassium chloroaurate.

[0026] In one embodiment, the wetting agent is one or more of ethanol, ethylene glycol, and glycerin.

[0027] In one embodiment, during the flotation step, the volume-to-mass ratio of the wetting agent to the waste printed circuit board is 0.5–2 ml / g, and the solid-liquid ratio, i.e., the mass-to-volume ratio of the waste printed circuit board to ethanol and water, is 50–150 g / L.

[0028] The basic principle of this invention is as follows:

[0029] In the electro-oxidative leaching and simultaneous electrowinning process for copper recovery, CuSO4 in the electrolyte can react with NH3·H2O, (NH4)2SO4, and ethylenediamine (en) to form Cu(NH3)4. 2+ Cu(en)2 2+ Etc., Cu(en)2 2+ stability constant (1×10) 20 The value is much greater than that of Cu(NH3)4. 2+ The stability constant (4.8 × 10⁻⁶) 12 Meanwhile, its oxidation potential is higher than that of the latter, which improves the oxidation capacity and stability of the electrolyte. Cu(en)2 2+ and Cu(NH3)4 2+ It reacts with copper in the circuit board to form Cu(en). + Cu(NH3)2 + The main reactions in the electrolytic cell are as follows:

[0030] Anode region reaction:

[0031] Cu(en)2 2+ +Cu→2Cu(en) +

[0032] Cu(NH3)4 2+ +Cu→2Cu(NH3)2 +

[0033] 2NH4 + →N2+8H + +6e -

[0034] 4OH - →2H₂O + O₂ + 4e -

[0035] Cathode region reaction:

[0036] Cu(NH3)4 2+ +e- →Cu(NH3)2 + +2NH3

[0037] Cu(NH3)2 + +e - →Cu+2NH3

[0038] Cu(en)2 2+ +e - →Cu(en) + +en

[0039] Cu(en) + +e - →Cu+en

[0040] 2H2O+2e - →H2+OH -

[0041] When the electro-oxidation leaching and simultaneous electrowinning for gold recovery is performed after the electro-oxidation leaching and simultaneous electrowinning for copper recovery step, the electrolyte contains I... - In the anodic region, electro-oxidation generates I2, which reacts with potassium iodide in the electrolyte to generate I3. - I3 - It can react with gold in the circuit board to form AuI2. - AuI4 - Meanwhile, elemental gold is recovered in the cathode region through electrodeposition. The main reactions in the electrolytic cell are as follows:

[0042] Anode region reaction:

[0043] 2I - →I2+2e -

[0044] I2+I - →I3 -

[0045] 2H₂O→O₂+4H + +4e -

[0046] 2Au+I - +I3 - →2AuI2 -

[0047] 2Au+3I3 - →2AuI4 - +I -

[0048] Cathode region reaction:

[0049] AuI2 - +e -→Au+2I -

[0050] AuI4 - +3e - →Au+4I -

[0051] 2H2O+2e - →H2+OH -

[0052] I3 - +2e - →3I -

[0053] When the electro-oxidative leaching and simultaneous electrowinning gold recovery step is performed before the flotation step, waste printed circuit boards are used as the anode, and thiourea and sodium chloride are added to the electrolyte to achieve electro-oxidative leaching of gold. This is because Au[CS(NH2)2]2 + The stability constant of the coordination compound (9.1 × 10⁻⁶) 21 Greater than AuCl2 - Stability constant of the complex (1.0 × 10⁻⁶) 9 During the electrolysis process, gold is converted into Au[CS(NH2)2]2. + In the leaching process, sodium chloride acts as a conductive medium, accelerating the electromigration rate of ions in the solution and reducing resistance, thereby speeding up the leaching of gold from the anode and the electrodeposition of gold from the cathode. The main reactions in the electrolytic cell are as follows:

[0054] Anode region reaction:

[0055] Au + 2CS(NH2)2 → Au[CS(NH2)2]2 + +e -

[0056] Cathode region reaction:

[0057] Au[CS(NH2)2]2 + +e - →Au+2CS(NH2)2

[0058] 2H2O+2e - →H2+OH -

[0059] The above-described solution of the present invention has the following beneficial effects:

[0060] This invention provides a technical solution for the stepwise recovery of gold and copper from waste printed circuit boards. By adjusting the timing and conditions of the simultaneous electro-oxidation leaching and electrowinning step for gold recovery, two process flows can be formed: flotation-electro-oxidation leaching-simultaneous electrowinning for copper recovery-electro-oxidation leaching-simultaneous electrowinning for gold recovery, and electro-oxidation leaching-simultaneous electrowinning for gold recovery-flotation-electro-oxidation leaching-simultaneous electrowinning for copper recovery. This achieves the resource-based recovery of gold and copper from waste printed circuit boards, which is beneficial to improving resource utilization efficiency. In the recovery method of this invention, through flotation, simultaneous electro-oxidation leaching and electrowinning for copper recovery, and simultaneous electro-oxidation leaching and electrowinning for gold recovery processes, and by precisely controlling the electrolysis parameters, a high-purity cathode product can be obtained at the cathode, achieving green and efficient recovery of gold and copper.

[0061] In the process of recovering gold by simultaneous electro-oxidation leaching and electrowinning – flotation – simultaneous electro-oxidation leaching and electrowinning for copper recovery, this invention, through electrolysis kinetics research, discovered that by precisely controlling the electrolysis time of each waste printed circuit board in a thiourea-sodium chloride-chloroaurate electrolyte, it is possible to preferentially recover gold from the surface layer of the waste printed circuit board, reducing gold loss during pretreatment. At this time, the leaching rates of copper and nickel are low, thereby achieving the separation of gold from copper and nickel and reducing the separation difficulty in subsequent processes.

[0062] This invention uses flotation technology to separate plastics and enrich metals, which can reduce the amount of material to be processed in subsequent processing steps, thereby reducing reagent and energy consumption.

[0063] This invention employs an electro-oxidative leaching and electrowinning technique to recover copper. The electrolyte contains CuSO4, NH3·H2O, (NH4)2SO4, and ethylenediamine. CuSO4 reacts with NH3·H2O, (NH4)2SO4, and ethylenediamine to form Cu(NH3)4. 2+ Cu(en)2 2+ By adding ethylenediamine to the electrolyte, not only can the amount of ammonia used be reduced, but the copper recovery rate can also be accelerated. A smooth and dense copper-clad cathode can be obtained even at low current densities, with a copper recovery rate of over 90% and a purity of over 90%. Because the concentration of copper ions changes significantly during electrolysis, this invention uses a constant current method to control the current and maintain a constant current, thus preventing the concentration of Cu(NH3)4 in the solution from increasing. 2+ Cu(en)2 2+ The concentration is reduced, which decreases the electrodeposition efficiency, thereby ensuring the uniform generation of cathode electrodeposition products.

[0064] This invention employs a simultaneous electro-oxidation leaching and electrodeposition technology to recover gold. It recovers gold through constant voltage electrolysis and precisely controls the voltage parameters, i.e., the electrode potential. This ensures that the electro-oxidation leaching and electrodeposition processes are conducive to the occurrence of the main reaction and reduces the occurrence of side reactions. It achieves selective electro-oxidation leaching of gold at the anode, thereby realizing the stepwise recovery of gold and copper. Attached Figure Description

[0065] Figure 1 This is a process flow diagram of a method for stepwise recycling of gold and copper from waste printed circuit boards according to an embodiment of the present invention;

[0066] Figure 2 The XRD pattern of electrolytic gold obtained in Embodiment 1 of the present invention;

[0067] Figure 3 The XRD pattern of electrolytic copper obtained in Embodiment 1 of the present invention;

[0068] Figure 4 This is a process flow diagram of a method for stepwise recycling of gold and copper from waste printed circuit boards according to another embodiment of the present invention.

[0069] Figure 5 This invention relates to the electrolytic kinetics of gold recovery through simultaneous electro-oxidation leaching and electrowinning in the scheme of gold recovery by electro-oxidation leaching and copper recovery by flotation and simultaneous electro-oxidation leaching and electrowinning.

[0070] Figure 6 This is an EDS image of the circuit board before gold recovery during electro-oxidation leaching and simultaneous electrowinning in Embodiment 5 of the present invention;

[0071] Figure 7 This is an EDS image of the circuit board after gold recovery via electro-oxidation leaching and simultaneous electrowinning in Embodiment 5 of the present invention. Detailed Implementation

[0072] To make the technical problems, solutions, and advantages of this invention clearer, a detailed description will be provided below with reference to the accompanying drawings and specific embodiments. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0073] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other. Unless otherwise specified, the reagents and instruments used in the embodiments are conventional choices in the art. Experimental methods not specifying specific conditions in the embodiments are implemented according to conventional conditions, such as those described in literature, books, or methods recommended by the manufacturer.

[0074] Example 1

[0075] This embodiment provides a technical solution for the simultaneous recovery of copper and gold through flotation-electro-oxidation leaching-electrodeposition, the process flow of which is attached. Figure 1 As shown, it includes the following steps:

[0076] SA1 Flotation: Waste printed circuit boards are crushed to a particle size of less than 0.425mm. Ethanol is added to the flotation cell, with a volume-to-mass ratio of ethanol to waste printed circuit boards of 1ml / g. Water is added to make the solid-liquid ratio 100g / L. The flotation yields foam products and in-cell products. The yield of in-cell products is 66.43%, and the recovery rates of gold and copper are 94.82% and 92.57%, respectively.

[0077] SA2 electro-oxidation leaching with simultaneous electrowinning for copper recovery: The product in the tank is added to the anode chamber of the electrolytic cell. The anode and cathode chambers are separated by a double-layered acid- and alkali-resistant filter cloth. Titanium plates and DSA plates serve as the cathode and anode, respectively. An alkaline solution containing 0.2 mol / L CuSO4, 0.25 mol / L (NH4)2SO4, 0.2 mol / L NH3·H2O, and 0.4 mol / L ethylenediamine is used as the electrolyte, with a solid-liquid ratio of 20 g / L. The power is turned on, and the current density is set to 15 mA / cm². 2 After 5 hours of electrolysis, the electrodeposited copper was recovered from the cathode plate, yielding a copper product with a purity of 99.96% and a copper recovery rate of 98.03%.

[0078] SA3 Electro-oxidation Leaching with Simultaneous Electrodeposition for Gold Recovery: The leaching residue obtained in step SA2 was placed in an electrolytic cell, with carbon fiber and DSA plate as the cathode and anode, respectively. In an electrolyte of 25 g / L potassium iodide, the electrolysis voltage was set to 4 V, the solid-liquid ratio to be 125 g / L, and after electrolysis for 2 hours, the electrodeposited gold was recovered from the cathode plate. The leaching rate of electro-oxidation gold was 99.18%, and the recovery rate of electrodeposited gold reached 91.59%.

[0079] like Figure 2 The image shown is the XRD pattern of the electrolytic gold obtained in this embodiment. Figure 3 The image shown is the XRD pattern of the electrolytic copper obtained in this embodiment. Figure 2 and Figure 3 This proves that high-purity gold and copper were obtained, respectively.

[0080] Example 2

[0081] The steps were the same as in Example 1. The difference was that the concentration of (NH4)2SO4 in step SA2 was 0.20 mol / L, and the electrolysis voltage in step SA3 was 5V. The results showed that copper with a purity of 99.87% was obtained on the cathode plate, and the recovery rate of copper electrodeposited at the cathode was 93.34%; the leaching rate of electro-oxidized gold was 97.77%, and the recovery rate of electrodeposited gold was 85.99%.

[0082] Example 3

[0083] The steps are the same as in Example 1, except that the current density in step SA2 is 20 mA / cm². 2In step SA3, the potassium iodide concentration was 20 g / L. The results showed that copper with a purity of 99.91% was obtained on the cathode plate, and the recovery rate of copper electrodeposited at the cathode was 96.05%; the leaching rate of electro-oxidized gold was 90.28%, and the recovery rate of electrodeposited gold was 81.52%.

[0084] Example 4

[0085] The steps were the same as in Example 1. The difference was that the ammonia concentration in step SA2 was 3 mol / L and the solid-liquid ratio in step SA3 was 200 g / L. The results showed that copper with a purity of 99.95% was obtained on the cathode plate, and the recovery rate of cathode electrodeposited copper reached 94.33%; the leaching rate of electro-oxidized gold was 89.37%, and the recovery rate of electrodeposited gold reached 85.39%.

[0086] Example 5

[0087] This embodiment provides a technical solution for the simultaneous electro-oxidation leaching and electrowinning recovery of gold, followed by flotation and simultaneous electro-oxidation leaching and electrowinning recovery of copper. The process flow is shown in the attached figure. Figure 4 As shown, it includes the following steps:

[0088] SB1 electro-oxidation leaching with simultaneous electrowinning for gold recovery: using the metal surface layer of waste printed circuit boards as the anode and carbon fiber as the cathode, with 2wt% thiourea and 2wt% sodium chloride and 35mg / L AuCl4. - The mixed solution was used as the electrolyte. The distance between the anode and cathode was adjusted to 5 cm, the DC power supply voltage was 2V, and the electrolysis time for each waste printed circuit board was 10s. A total of 15 waste printed circuit boards were replaced. The electro-oxidation leaching rate of gold reached 98.00%, and the recovery rate of electro-gold reached 91.36%.

[0089] like Figure 5 As shown, electrolysis kinetics studies revealed that in a thiourea-sodium chloride-chloroaurate electrolyte, precisely controlling the electrolysis time of each waste printed circuit board to 5–15 seconds can preferentially recover gold from the surface layer of the waste printed circuit board, reducing gold loss during pretreatment. At this time, the concentrations of copper and nickel are still low, thus achieving separation of gold from copper and nickel and reducing the difficulty of separation in subsequent processes. Figure 6 and Figure 7 The figures shown are EDS (Electro-Dispersive Oxidation) spectra of the circuit board before and after gold recovery via simultaneous electro-oxidation leaching and electrowinning in this embodiment. Figure 6 and Figure 7 It can be seen that, after electro-oxidation leaching, the gold on the outermost layer of the waste printed circuit board is basically completely leached out;

[0090] SB2 Flotation: The waste printed circuit boards processed in step SB1 are taken out and crushed to a particle size of less than 0.425mm. Ethanol is added to the flotation cell, with a volume-to-mass ratio of ethanol to waste printed circuit boards of 1ml / g. Water is added to make the solid-liquid ratio 100g / L. The flotation yields foam products and products in the cell. The yield of products in the cell is 65.78%, and the recovery rates of gold and copper are 95.07% and 93.05%, respectively.

[0091] SB3 Electro-oxidation Leaching with Simultaneous Electrowinning for Copper Recovery: The product from step SB3 is added to the anode chamber of the electrolytic cell. The anode and cathode chambers are separated by a double-layered acid- and alkali-resistant filter cloth. Titanium plates and DSA plates serve as the cathode and anode, respectively. An alkaline solution containing 0.2 mol / L CuSO4, 0.25 mol / L (NH4)2SO4, 0.2 mol / L NH3·H2O, and 0.4 mol / L ethylenediamine is used as the electrolyte, with a solid-liquid ratio of 20 g / L. The power is turned on, and the current density is set to 15 mA / cm². 2 After 5 hours of electrolysis, the electrodeposited copper was recovered from the cathode plate, yielding a copper product with a purity of 99.95%, and the recovery rate of electrodeposited copper reached 98.96%.

[0092] Example 6

[0093] The steps were the same as in Example 5. The difference was that the sodium chloride content in step SB1 was 1 wt%, and the ethylenediamine concentration in step SB3 was 0.5 mol / L. The results showed that the gold leaching rate reached 90.84% ​​and the gold recovery rate reached 82.39% in a single electrolysis process. Copper with a purity of 99.82% was obtained on the cathode plate, and the copper recovery rate of cathode electrodeposition reached 93.38%.

[0094] Example 7

[0095] The steps were the same as in Example 5. The difference was that the voltage in step SB1 was 1.8V and the solid-liquid ratio in step SB3 was 15g / L. The results showed that the gold leaching rate reached 93.43% and the recovery rate of electrodeposited gold reached 85.96% in a single electrolysis process. Copper with a purity of 99.90% was obtained on the cathode plate and the recovery rate of cathode electrodeposited copper reached 99.27%.

[0096] Example 8

[0097] The steps are the same as in Example 5. The difference is that the electrolysis time for each waste printed circuit board in step SB1 is 15 seconds, and a total of 15 waste printed circuit boards are replaced. The electrolysis time in step SB3 is 5.5 hours. The results show that the gold leaching rate reaches 99.91% and the recovery rate of electrodeposited gold reaches 89.37% in a single electrolysis process. Copper with a purity of 99.85% is obtained on the cathode plate, and the recovery rate of cathode electrodeposited copper reaches 99.24%.

[0098] Comparative Example 1

[0099] Compared with Example 1, the difference is that ethylenediamine is not added in step SA2. Other operations and parameters are the same as in Example 1. The results showed that copper with a purity of 99.93% was obtained on the cathode plate, and the recovery rate of copper electrodeposited at the cathode was only 8.63%. This indicates that ethylenediamine has little effect on the electro-oxidation process. However, during the electrodeposition process, ethylenediamine coordinates with copper ions in the solution, which can effectively promote the electrodeposition reaction. The lack of ethylenediamine seriously affects the electrodeposition of copper.

[0100] Comparative Example 2

[0101] Compared with Example 5, the difference is that thiourea is not added to the electrolyte in step SB1. Other operations and parameters are the same as in Example 5. The results showed that the gold leaching rate was almost 0 in a single electrolysis process, and gold could not be recovered by electrodeposition. This indicates that the coordination of thiourea with gold in the electrolysis process is the dominant role in leaching gold.

[0102] Comparative Example 3

[0103] Compared with Example 5, the difference is that sodium chloride is not added to the electrolyte in step SB1. Other operations and parameters are the same as in Example 5. The results showed that the electro-oxidation leaching rate of gold was only 54.92%, and the recovery rate of electro-deposited gold was only 63.58%. Both the leaching rate and recovery rate were lower than those of Example 5. The main reason is that sodium chloride can enhance the conductivity of the electrolyte. Without the addition of sodium chloride, the conductivity of the electrolyte decreases, which affects the electro-oxidation leaching process.

[0104] Comparative Example 4

[0105] Compared with Example 5, the difference is that the DC voltage in step SB1 is 1.4V, while other operations and parameters are the same as in Example 5. The results showed that the gold leaching rate in a single electrolysis process was only 6.82%, and the recovery rate of electrodeposited gold was only 0.013%, indicating that a sufficiently high DC voltage must be maintained in this step to leach gold.

[0106] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for the stepwise recovery of gold and copper from waste printed circuit boards, characterized in that, This includes simultaneous electrochemical oxidation leaching and electrowinning for copper recovery and simultaneous electrochemical oxidation leaching and electrowinning for gold recovery; The flotation step specifically includes: crushing waste printed circuit boards to a particle size of less than 0.425mm, then mixing them with water and wetting agent for flotation to obtain foam products and products in the tank; The specific steps of the electro-oxidation leaching and simultaneous electrowinning copper recovery process include: placing the product in the tank into an electrolytic cell, performing electro-oxidation leaching with a copper ammonia alkaline electrolyte, and simultaneously recovering copper by electrowinning to obtain leaching residue and electrowinning copper; the copper ammonia alkaline electrolyte contains CuSO4, (NH4)2SO4, NH3·H2O and ethylenediamine; When the electro-oxidation leaching and simultaneous electrowinning gold recovery step is performed after the electro-oxidation leaching and simultaneous electrowinning copper recovery step, it specifically includes: placing the leaching residue obtained from the electro-oxidation leaching and simultaneous electrowinning copper recovery step into an electrolytic cell, performing electro-oxidation leaching with potassium iodide electrolyte, and simultaneously recovering gold by electrowinning. When the electro-oxidation leaching and simultaneous electrowinning gold recovery step is performed before the flotation step, it specifically includes: using waste printed circuit boards as anodes, electro-oxidation leaching of gold is carried out in a thiourea-sodium chloride-chloroaurate electrolyte, while simultaneously recovering gold by electrowinning. Within the same electrowinning cycle, the waste printed circuit boards with the anode are replaced at least 10 times, so that gold is enriched at the cathode.

2. The method according to claim 1, characterized in that, In the copper ammonia alkaline electrolyte, the concentration of CuSO4 is 0.05–0.3 mol / L, the concentration of (NH4)2SO4 is 0.1–0.3 mol / L, the concentration of NH3·H2O is 0.1–0.3 mol / L, and the concentration of ethylenediamine is 0.1–0.6 mol / L.

3. The method according to claim 1, characterized in that, In the electro-oxidation leaching and simultaneous electrowinning copper recovery step, the current density is 10–30 mA / cm². 2 The electrolysis time is 3 to 7 hours, and the solid-liquid ratio is 10 to 40 g / L.

4. The method according to claim 1, characterized in that, In the electro-oxidation leaching and simultaneous electrowinning copper recovery step, the anode is selected from any one of DSA, graphite and titanium mesh, and the cathode is a titanium plate.

5. The method according to claim 1, characterized in that, When the electro-oxidation leaching and simultaneous electrowinning for gold recovery step is performed after the electro-oxidation leaching and simultaneous electrowinning for copper recovery step, the concentration of potassium iodide in the potassium iodide electrolyte is 5-30 g / L, the electrolysis voltage is 2-6 V, the electrolysis time is 0.5-3 h, and the solid-liquid ratio is 100-200 g / L.

6. The method according to claim 1, characterized in that, When the electro-oxidation leaching simultaneous electrowinning gold recovery step is performed after the electro-oxidation leaching simultaneous electrowinning copper recovery step, the anode is selected from any one of DSA, graphite and titanium mesh, and the cathode is selected from any one of graphite, titanium mesh and carbon fiber.

7. The method according to claim 1, characterized in that, When the electro-oxidation leaching and simultaneous electrowinning gold recovery step is performed before the flotation step, the thiourea-sodium chloride-chloroaurate electrolyte contains 0.5wt% to 4wt% thiourea, 0.5wt% to 4wt% sodium chloride, and 30 to 40 mg / L chloroaurate. The cathode is selected from any one of graphite, titanium mesh, and carbon fiber. The distance between the anode and cathode is 3 to 10 cm. The electrolysis voltage is 1.5 to 4 V. The electrolysis time for each waste printed circuit board is 5 s to 18 min.

8. The method according to any one of claims 1 to 7, characterized in that, The chloroaurate ion is derived from any one or more of tetrachloroauric acid, sodium chloroaurate, or potassium chloroaurate.

9. The method according to any one of claims 1 to 7, characterized in that, The wetting agent is one or more of ethanol, ethylene glycol, and glycerin.

10. The method according to any one of claims 1 to 7, characterized in that, In the flotation step, the volume-to-mass ratio of the wetting agent to the waste printed circuit board is 0.5–2 ml / g, and the solid-liquid ratio is 50–150 g / L.

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