Electrochemical gradient extraction method for gold and copper in electronic waste

Abstract

The invention discloses a method for electrochemical gradient extraction of gold and copper in electronic waste, which comprises the following steps: taking a mixed solution composed of sulfuric acid and copper sulfate as a first electrolyte, taking the electronic waste as an anode, carrying out a first electrolytic reaction, then taking out the degolded electronic waste, and carrying out solid-liquid separation and drying on an anode chamber solution to obtain the gold and copper in the electronic waste. Gold foil is obtained; and taking a mixed solution consisting of sodium chloride, sulfuric acid, copper sulfate and diethylenetriamine pentaacetic acid as a second electrolyte, adding the degolded electronic waste into the anode chamber, carrying out a second electrolytic reaction, then collecting sediments in the cathode chamber, and passivating, cleaning and drying to obtain the copper foil. According to the method, gold in the electronic waste is directly extracted through an electrochemical method, copper is continuously extracted through a slurry electrolysis method, the process of extracting gold and copper from the electronic waste is shortened, the recovery rate of obtained gold and copper is high, and the purity of copper is high; the used medicament is simple, easy to treat and good in environmental benefit.

Description

Technical Field

[0001] The present invention relates to the technical field of electronic waste resource recovery, and in particular to a method for electrochemical stepwise extraction of gold and copper from electronic waste. Background Art

[0002] Electronic waste is a new type of waste brought about by modern technological development. Efficiently extracting valuable components from electronic waste is crucial for achieving sustainable resource utilization and resolving environmental issues caused by electronic waste.

[0003] Currently, the main technologies for extracting gold and copper from electronic waste are pyrometallurgical and hydrometallurgical methods. The pyrometallurgical method uses fluidized bed incineration to melt gold and other precious metals into copper. Electrolytic refining then produces gold and other precious metals in the anode slag and copper at the cathode. Because the incineration process produces toxic gases such as dioxins, which pollute the environment, it also requires high equipment and energy consumption, making it less widely used. The hydrometallurgical method, with its flexible operation and low equipment investment, is widely used to extract valuable metals from electronic waste. The hydrometallurgical method requires first crushing the electronic waste to fully expose the metals within. Then, the waste is cleaned and base metals such as Cu, Fe, Ni, Sn, and Pb are leached from the waste using alkaline or acidic solutions. The cleaned waste powder is then treated with specialized leaching agents such as aqua regia and cyanide to dissolve the gold. The low concentration of the gold leaching solution requires enrichment through extraction and stripping, followed by reduction to obtain elemental gold. Finally, the copper in the waste is recovered by electrodeposition from the cleaned solution. However, the above traditional methods have the following defects: (1) The gold extraction process is long and the recovery rate is low: The traditional method of extracting gold from electronic waste requires four steps: leaching - extraction - stripping - reduction. The operation process is long and a part of the gold will be lost in each step, resulting in a low final gold extraction rate; (2) Special gold leaching agents are required, which poses great environmental hazards: Traditional methods require the use of highly toxic and corrosive agents such as cyanide and aqua regia to leach gold from electronic waste. The waste gas, wastewater, and tailings generated during the leaching process are difficult to handle, which poses great environmental hazards. (3) The copper extraction process is long and the purity is low: The traditional method of extracting copper from electronic waste is to separate the leaching and recovery processes. The process is long and the impurity removal solution contains impurity metals such as Fe, Ni, Sn, and Pb. During the electroplating recovery, the impurity metals are deposited at the same time, and the purity of the recovered copper is low.

[0004] Therefore, there is an urgent need to provide a new process for extracting gold and copper from electronic waste to solve the above problems. Summary of the Invention

[0005] The purpose of the present invention is to overcome the above technical deficiencies and propose a method for electrochemical cascade extraction of gold and copper from electronic waste, thereby solving the technical problems in the prior art of extracting gold and copper from electronic waste, such as long process, low gold recovery rate, low copper purity and great environmental harm.

[0006] The present invention provides a method for electrochemical cascade extraction of gold and copper from electronic waste, comprising the following steps: A mixed solution of sulfuric acid and copper sulfate is used as the first electrolyte, and the electronic waste is used as the anode to carry out a first electrolysis reaction. The electronic waste after gold removal is then taken out, and the anode chamber solution is subjected to solid-liquid separation and dried to obtain gold foil. A mixed solution of sodium chloride, sulfuric acid, copper sulfate and diethylenetriaminepentaacetic acid is used as the second electrolyte, and electronic waste after gold removal is added to the anode chamber to perform a second electrolysis reaction, and then the sediment in the cathode chamber is collected, passivated, cleaned and dried to obtain copper foil; wherein, In the first electrolyte, the concentration of sulfuric acid is 0.05-0.25 mol / L, and the concentration of copper sulfate pentahydrate is 5-50 mmol / L; in the second electrolyte, the concentration of sodium chloride is 0.4-1.6 mol / L, the concentration of sulfuric acid is 0.05-0.5 mol / L, the concentration of copper sulfate pentahydrate is 20-100 mmol / L, and the concentration of diethylenetriaminepentaacetic acid is 5-30 mmol / L.

[0007] Compared with the prior art, the present invention has the following beneficial effects: The present invention adopts an electrochemical method to directly extract gold from electronic waste, and adopts a slurry electrolysis method to further extract copper, thereby shortening the process of extracting gold and copper from electronic waste, and achieving a high recovery rate of gold and copper and high purity of copper. The reagents used in the present invention are simple, easy to handle, and have good environmental benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 1 is a graph showing the change in the gold extraction rate from discarded communication circuit boards over time in Example 2 of the present invention. DETAILED DESCRIPTION

[0009] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0010] The present invention provides a method for electrochemical cascade extraction of gold and copper from electronic waste, comprising the following steps: S1. Using a mixed solution of sulfuric acid and copper sulfate as a first electrolyte and electronic waste as an anode, a first electrolysis reaction is performed, and then the electronic waste after gold removal is removed. The anode chamber solution is subjected to solid-liquid separation and dried to obtain gold foil; S2. A mixed solution of sodium chloride, sulfuric acid, copper sulfate and diethylenetriaminepentaacetic acid (DTPA) is used as the second electrolyte, and the electronic waste after gold removal is added to the anode chamber to carry out the second electrolysis reaction. The sediment in the cathode chamber is then collected, passivated, cleaned and dried to obtain copper foil.

[0011] The principles of the present invention are as follows: Printed circuit boards (PCBs), commonly found in electronic waste, are constructed by laminating and pressing together several layers of copper-clad laminates and several insulating organic protective layers (including, but not limited to, fiberglass, brominated flame retardants, and epoxy resins). The outermost copper-clad laminate is responsible for exchanging electrical signals with the outside world and is partially exposed to air. To prevent this copper from severe oxidation due to prolonged exposure to air, it is typically plated with gold to insulate it from air. Nickel acts as a layer between the copper and gold, further strengthening the bond between the two.

[0012] During the first electrolytic reaction, the electronic waste acts as the anode, and the copper inside the electronic waste acts as a natural conductor, transmitting the current to the nickel-gold coating on the surface. The outermost gold coating does not corrode due to its inertness, while the nickel in the middle layer is leached, and the reaction is as follows:

[0013] The corrosion of the nickel layer causes a cavity to form under the gold layer. As the cavity grows, the solution contacts the copper underneath, and the reaction occurs as follows:

[0014] When the voids are large enough, the bond between the gold layer and the electronic waste weakens and the gold layer eventually falls off the electronic waste.

[0015] During the first electrolysis reaction, the main reaction occurring at the cathode is:

[0016] During the first electrolysis reaction, the side reaction at the cathode is:

[0017] During the second electrolysis reaction, Cu 2+ As an oxidant, the reaction in the anode chamber is:

[0018] Leaching copper from electronic waste in the anode chamber and generating a large amount of CuCl2- , these ions react at the anode as follows:

[0019] Achieve circulation of the oxidant in the second electrolyte.

[0020] During the second electrolysis reaction, the main reaction occurring at the cathode is:

[0021] Cu in solution 2+ It is reduced to copper at the cathode.

[0022] The following side reactions occur at the anode and cathode respectively:

[0023]

[0024] In this embodiment, the electronic waste includes several layers of copper-clad laminates and several protective layers, with each layer of copper-clad laminate alternating with each protective layer. The protective layer between two adjacent layers of copper-clad laminates is an insulating organic protective layer, while the protective layer on the outermost copper-clad laminate is composed of an insulating organic protective layer and a conductive metal protective layer. In this electronic waste structure, the outermost copper-clad laminate is used to exchange electrical signals with the outside world. It is partially exposed to air and protected by the conductive metal protective layer, while the remaining portion is protected by the insulating organic protective layer. The remaining copper-clad laminates are protected by the insulating organic protective layer.

[0025] Furthermore, the conductive metal protective layer includes a nickel plating layer and a gold plating layer, and two sides of the nickel plating layer are in contact with the outermost copper clad plate and the gold plating layer respectively.

[0026] Furthermore, the material of the insulating organic protective layer includes but is not limited to glass fiber, brominated flame retardant, epoxy resin, etc.

[0027] In this embodiment, the electronic waste is printed circuit board (PCB) type electronic waste, including but not limited to discarded CPUs, discarded mobile phone circuit boards, discarded communication circuit boards, discarded memory sticks, etc.

[0028] In the first electrolyte, the concentration of sulfuric acid is 0.05-0.25 mol / L, including but not limited to 0.05 mol / L, 0.1 mol / L, 0.15 mol / L, 0.2 mol / L, 0.25 mol / L, etc., and the concentration of copper sulfate pentahydrate is 5-50 mmol / L, including but not limited to 5 mmol / L, 10 mmol / L, 20 mmol / L, 30 mmol / L, 40 mmol / L, 50 mmol / L, etc. In the first electrolyte, sulfuric acid provides hydrogen ions, which can be consumed in the side reaction to reduce the pH of the electrolyte + stabilize the pH of the electrolyte after electrolysis and maintain Cu 2+ , Ni 2+ In the electrolyte, the stability prevents the pH from rising during electrolysis, which causes the electrolyte to fail; copper sulfate mainly provides copper ions, which can be reduced to inhibit the hydrogen evolution side reaction. If the concentration of sulfuric acid is too low, there are not enough hydrogen ions in the solution, and the effect of stabilizing the pH is poor; if the concentration of sulfuric acid is too high, there are too many hydrogen ions in the solution, and the hydrogen evolution side reaction is enhanced during electrolysis. If the concentration of copper sulfate is too low, it cannot provide sufficient copper ions to be reduced, which is not conducive to inhibiting the hydrogen evolution side reaction; if the concentration of copper sulfate is too high, the inhibitory effect of copper ions on the cathode hydrogen evolution side reaction is almost no longer increased.

[0029] In the first electrolysis reaction process, the cathode includes but is not limited to titanium plate, stainless steel plate, copper plate, etc.

[0030] In the first electrolysis reaction process, the diaphragm is an acid-resistant filter screen, and the pore size is 25-75 μm, including but not limited to 25 μm, 50 μm, 75 μm, etc. By controlling the pore size of the diaphragm within the above range, the present application can make the liquid pass freely and collect the detached gold foil in the anode chamber solution.

[0031] Specifically, the material of the diaphragm includes but is not limited to polyester fiber (PET) or polypropylene (PP), etc.

[0032] In this embodiment, during the first electrolysis reaction, the voltage is 0.8-2.5 V, including but not limited to 0.8 V, 1.2 V, 1.6 V, 2 V, 2.5 V, etc., the electrolysis time is 6-24 h, including but not limited to 6 h, 10 h, 16 h, 20 h, and 24 h, the electrolysis temperature is 15-45°C, including but not limited to 15°C, 25°C, 35°C, and 45°C, etc., and the stirring speed of the anode chamber is 100-500 r / min, including but not limited to 100 r / min, 200 r / min, 300 r / min, 400 r / min, and 500 r / min, etc. If the voltage is too high, the side reactions during the electrolysis process will be enhanced; if the voltage is too low, the electrolysis reaction will not occur; if the electrolysis time is too short, the gold extraction rate will be reduced; if the electrolysis time is too long, the gold extraction efficiency will be reduced.

[0033] In this embodiment, in the second electrolyte, the concentration of sodium chloride is 0.4-1.6 mol / L, including but not limited to 0.4 mmol / L, 0.8 mmol / L, 1.2 mmol / L, 1.6 mmol / L, etc.; the concentration of sulfuric acid is 0.05-0.5 mol / L, including but not limited to 0.05 mol / L, 0.1 mol / L, 0.15 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, etc.; the concentration of copper sulfate pentahydrate is 20-100 mmol / L, including but not limited to 20 mmol / L, 40 mmol / L, 60 mmol / L, 80 mmol / L, 100 mmol / L, etc.; and the concentration of diethylenetriaminepentaacetic acid (DTPA) is 5-30 mmol / L, including but not limited to 5 mmol / L, 10 mmol / L, 20 mmol / L, 30 mmol / L, etc. In the second electrolyte, sodium chloride provides chloride ions, which can act as a complexing agent to accelerate the leaching of copper; sulfuric acid provides hydrogen ions, which can consume H in the side reaction. + After stabilizing the electrolyte pH, maintain Cu 2 + 、Fe 3+ 、Sn 2+ The stability of the electrolyte can prevent the pH from increasing during the electrolysis process and causing the electrolyte to become ineffective. Copper sulfate mainly provides copper ions, which can reduce copper ions and inhibit the hydrogen evolution side reaction. At the same time, sufficient copper ions can act as oxidants to efficiently leach copper from the powder. DTPA can be adsorbed by the copper recovered at the cathode, hindering the formation of hydrogen. +H2 is generated at the cathode interface. Suppressing the hydrogen evolution side reaction prevents a rise in the local pH at the cathode, preventing the deposition of impurity metals such as Fe and Sn as hydroxides, and improving the purity of the recovered copper. Simultaneously, weakening the hydrogen evolution side reaction allows the cathode copper to be deposited as copper foil rather than copper powder. If the chloride ion concentration is too low, the copper leaching rate is slow, and the copper leached from the anode does not have enough time to migrate to the cathode, increasing the cathode hydrogen evolution side reaction. If the chloride ion concentration is too high, the copper ions and chloride ions form a tight complex, making copper recovery at the cathode difficult. If the sulfuric acid concentration is too low, the solution lacks hydrogen ions, resulting in poor pH stabilization. If the sulfuric acid concentration is too high, the solution becomes overloaded with hydrogen ions, enhancing the hydrogen evolution side reaction during electrolysis. If the copper sulfate concentration is too low, insufficient copper ions are available for reduction, hindering the suppression of the hydrogen evolution side reaction and the efficient leaching of copper from the leached powder. If the copper sulfate concentration is too high, the leaching rate is no longer significantly increased, nor is the suppression of the cathode hydrogen evolution side reaction significantly increased. If the concentration of diethylenetriaminepentaacetic acid is too low, the morphology of copper recovered at the cathode is poor and it is not deposited in the form of copper foil; if the concentration of diethylenetriaminepentaacetic acid is too high, the complexing ability for copper ions is too strong, making it difficult to recover copper at the cathode.

[0034] In this embodiment, during the second electrolysis reaction, the de-goldened electronic waste is pre-crushed to a particle size of 100-1000 μm before being cleaned and dried. Because the electronic waste may contain copper-clad laminates, which are protected by glass fibers, brominated flame retardants, and other agents, preventing them from fully contacting the solution and hindering direct leaching, pre-crushing them can improve leaching efficiency.

[0035] In this embodiment, during the second electrolysis reaction, the diaphragm is an acid-resistant filter mesh having a pore size of 50-100 μm, including but not limited to 50 μm, 75 μm, and 100 μm. By controlling the pore size of the diaphragm within this range, the present invention allows liquid to pass freely while preventing anode electronic waste powder from entering the cathode chamber, thereby preventing contamination of the cathode recovered copper.

[0036] Specifically, the material of the diaphragm includes but is not limited to polyester fiber (PET) or polypropylene (PP).

[0037] In this embodiment, during the second electrolysis reaction, the anode includes but is not limited to a graphite plate, titanium-based lead dioxide, an iridium-coated tantalum titanium plate, an iridium-coated tantalum titanium mesh, and the like.

[0038] In this embodiment, during the second electrolysis reaction, the cathode includes but is not limited to a titanium plate, a stainless steel plate, a copper plate, and the like.

[0039] In this embodiment, during the second electrolysis reaction, the content of the electronic waste after gold removal in the second electrolyte is 40-200 g / L, including but not limited to 40 g / L, 50 g / L, 60 g / L, 80 g / L, 100 g / L, 120 g / L, 160 g / L, 200 g / L, etc.

[0040] In this embodiment, during the second electrolysis reaction, the current density is 5-50 mA / cm 2 , including but not limited to 5mA / cm 2 , 10 mA / cm 2 , 12.5 mA / cm 2 , 20 mA / cm 2 , 30 mA / cm 2 , 40 mA / cm 2 , 50 mA / cm 2 The electrolysis time is 8-24 hours, including but not limited to 8 hours, 12 hours, 16 hours, 20 hours, and 24 hours. The electrolysis temperature is 15-45°C, including but not limited to 15°C, 25°C, 35°C, and 45°C. The stirring speed of the anode chamber is 200-500 r / min, including but not limited to 200 r / min, 300 r / min, 400 r / min, and 500 r / min. If the current density is too high, the side reactions of the electrolysis reaction will be more serious, which is not conducive to the recovery of high-purity copper at the cathode. If the current density is too low, the voltage will drop, and copper recovery will be impossible. If the electrolysis time is too short, the copper extraction rate will be low. If the electrolysis time is too long, the copper extraction efficiency will be low.

[0041] In this embodiment, passivation is performed by immersing in a benzotriazole solution.

[0042] Furthermore, the concentration of the benzotriazole solution is 2-10 g / L, including but not limited to 2 g / L, 5 g / L, 8 g / L, 10 g / L, etc.

[0043] Furthermore, the soaking temperature is room temperature, and the soaking time is 2 to 10 minutes, including but not limited to 2 minutes, 5 minutes, 8 minutes, 10 minutes, etc.

[0044] To avoid redundancy, in the following embodiments and comparative examples of the present invention, the calculation formulas for the gold extraction rate and the copper extraction rate are as follows: Gold extraction rate = (collected gold / total gold in anode electronic waste) × 100% Copper extraction rate = (1-remaining copper in anode electronic waste / total copper in anode electronic waste) × 100%.

[0045] Test of the content of each element in gold foil and copper foil (powder): Dissolve in aqua regia, and after constant volume, use flame atomic absorption spectrometry to test the concentration of each element ion in the solution, and then multiply it by the volume of the constant volume solution to convert it into content.

[0046] Example 1 (1) Prepare 1 L of a first electrolyte solution containing 0.1 mol / L sulfuric acid and 30 mmol / L copper sulfate pentahydrate. Add the first electrolyte solution to an electrolytic cell with 10 discarded CPUs as the anode and a titanium plate as the cathode. A 75 μm PET mesh is used to separate the cathode and cathode chambers. The electrolysis reaction voltage is 2 V, the electrolysis temperature is room temperature, the electrolysis time is 16 h, and the stirring speed of the anode chamber is 200 r / min. After the electrolysis reaction, remove the discarded CPUs, filter the anode chamber solution, and dry it to obtain gold foil.

[0047] (2) The waste CPU after gold removal was crushed to a particle size of 100-1000 μm, and then washed and dried to obtain waste CPU powder; 500 mL of the second electrolyte was prepared, wherein the concentration of sodium chloride was 1.5 mol / L, the concentration of sulfuric acid was 0.5 mol / L, the concentration of copper sulfate pentahydrate was 100 mmol / L, and the concentration of DTPA was 10 mmol / L; the above second electrolyte was added to the electrolytic cell, and the anode and cathode chambers were separated by a 50 μm PET mesh. A graphite plate was used as the anode and a titanium plate was used as the cathode. 25 g of waste CPU powder was added to the anode chamber, and the current density of the electrolysis reaction was 50 mA / cm 2 The electrolysis temperature was room temperature, the electrolysis time was 8 hours, and the stirring speed in the anode chamber was 200 r / min. After the electrolysis reaction, the sediment in the cathode chamber was collected, passivated (immersed in 5g / L benzotriazole solution at room temperature for 5 minutes), cleaned, and dried to obtain copper foil.

[0048] Table 1 Content of each element in the gold foil obtained in Example 1

[0049] Table 2 Content of each element in the copper foil obtained in Example 1

[0050] Referring to Tables 1 and 2, the gold extraction rate from the discarded CPUs in this embodiment is 93.6%, and the gold content in the gold foil is 81.3%. The copper extraction rate from the discarded CPUs in this embodiment is 91.5%, and the copper content in the copper foil is 98.8%.

[0051] Example 2 (1) Prepare 1 L of a first electrolyte solution containing 0.1 mol / L sulfuric acid and 50 mmol / L copper sulfate pentahydrate. Add the first electrolyte solution to an electrolytic cell with 10 discarded communication circuit boards as the anode and a titanium plate as the cathode. A 75 μm PET mesh is used to separate the anode and cathode chambers. The electrolysis reaction is performed at a voltage of 2.5 V, room temperature, and a time of 10 h. The stirring speed of the anode chamber is 400 rpm. After the electrolysis reaction, remove the discarded communication circuit boards, filter, and dry the anode chamber solution to obtain gold foil.

[0052] (2) The de-goldened waste communication circuit boards were crushed to a particle size of 100-1000 μm, and then washed and dried to obtain waste communication circuit board powder; 500 mL of a second electrolyte was prepared, wherein the concentration of sodium chloride was 1.2 mol / L, the concentration of sulfuric acid was 0.15 mol / L, the concentration of copper sulfate pentahydrate was 60 mmol / L, and the concentration of DTPA was 20 mmol / L; the above second electrolyte was added to the electrolytic cell, and a 75 μm PET mesh was used to separate the anode and cathode chambers. A graphite plate was used as the anode and a titanium plate was used as the cathode. 50 g of waste communication circuit board powder was added to the anode chamber, and the current density of the electrolysis reaction was 10 mA / cm 2 The electrolysis temperature was room temperature, the electrolysis time was 24 hours, and the stirring speed in the anode chamber was 400 r / min. After the electrolysis reaction, the sediment in the cathode chamber was collected, passivated (immersed in 5g / L benzotriazole solution at room temperature for 5 minutes), cleaned, and dried to obtain copper foil.

[0053] In this example, the gold extraction rate from discarded communication circuit boards was 100%, and the gold content in the gold foil was 89.7%. In this example, the copper extraction rate from discarded communication circuit boards was 97.6%, and the copper content in the copper foil was 99.9%.

[0054] See also Figure 1 ,pass Figure 1 It can be seen that with the extension of electrolysis time, the gold extraction rate gradually increases. When the electrolysis time is 10h, the gold extraction rate reaches 100%.

[0055] Example 3 (1) Prepare 1 L of a first electrolyte solution containing 0.1 mol / L sulfuric acid and 30 mmol / L copper sulfate pentahydrate. Add the first electrolyte solution to an electrolytic cell with five discarded memory sticks as the anode and a titanium plate as the cathode. A 75 μm PET mesh is used to separate the anode and cathode compartments. The electrolysis reaction is performed at a voltage of 1.6 V, room temperature, and a time of 10 h. The stirring speed of the anode compartment is 200 rpm. After the electrolysis reaction, remove the discarded memory sticks, filter, and dry the anode compartment solution to obtain gold foil.

[0056] (2) The discarded memory sticks after gold removal were crushed to a particle size of 100-1000 μm, and then washed and dried to obtain discarded memory stick powder; 500 mL of the second electrolyte was prepared, wherein the concentration of sodium chloride was 1.6 mol / L, the concentration of sulfuric acid was 0.15 mol / L, the concentration of copper sulfate pentahydrate was 100 mmol / L, and the concentration of DTPA was 20 mmol / L; the above second electrolyte was added to the electrolytic cell, and the anode and cathode chambers were separated by a 75 μm PET mesh. A graphite plate was used as the anode and a titanium plate was used as the cathode. 30 g of discarded memory stick powder was added to the anode chamber, and the current density of the electrolysis reaction was 12.5 mA / cm 2 The electrolysis temperature was room temperature, the electrolysis time was 20 hours, and the stirring speed in the anode chamber was 200 r / min. After the electrolysis reaction, the sediment in the cathode chamber was collected, passivated (immersed in 5g / L benzotriazole solution at room temperature for 5 minutes), cleaned, and dried to obtain copper foil.

[0057] In this example, the gold extraction rate from discarded memory sticks was 94.7%, and the gold content in the gold foil was 83.4%. In this example, the copper extraction rate from discarded memory sticks was 98.1%, and the copper content in the copper foil was 99.6%.

[0058] Comparative Example 1 Compared with Example 1, the only difference is that in step (1), the voltage of the electrolysis reaction is 0 V.

[0059] The gold extraction rate of the discarded CPU in this comparative example is 0%. The reason is that the electrolytic reaction voltage in this comparative example is 0 V, and the Ni and Cu under the gold plating on the surface of the discarded CPU are not corroded. The gold plating is firmly bonded to the CPU and cannot fall off.

[0060] Comparative Example 2 Compared with Example 1, the only difference is that in step (1), the voltage of the electrolysis reaction is 4 V.

[0061] The gold extraction rate of the discarded CPU in this comparative example is 23%. The reason is that the electrolytic reaction voltage in this comparative example is 4 V, and a serious oxygen evolution reaction occurs on the surface of the discarded CPU. The surface of the gold plating is covered with a large number of bubbles. The Ni and Cu below are difficult to contact with the electrolyte, and ions cannot be formed to enter the solution. The gold plating is firmly bonded to the CPU and is difficult to fall off.

[0062] Comparative Example 3 Compared with Example 1, the only difference is that in step (2), the DTPA concentration is 0 mmol / L.

[0063] This comparative example achieved an 83.9% copper extraction rate from scrap CPUs, with the copper content in the copper powder reaching 46.2%. This is due to the fact that the DTPA addition level was 0 mmol / L in this comparative example. During the slurry electrolysis process, a strong hydrogen evolution reaction occurred at the cathode, preventing the sediment from growing stably and resulting in a powdery deposit. Furthermore, the pH at the cathode increased, causing a large amount of impurity metals to precipitate as hydroxides at the cathode, resulting in a decrease in the purity of the copper recovered at the cathode.

[0064] Comparative Example 4 Compared with Example 1, the only difference is that in step (2), the sodium chloride concentration is 0 mmol / L.

[0065] This comparative example achieved a copper extraction rate of 37.3% from discarded CPUs, and the copper content in the copper powder was 74.5%. This is because the sodium chloride addition in this comparative example was 0 mmol / L, resulting in a lack of chloride ions in the electrolyte, making it difficult for the anode copper to undergo oxidation during the slurry electrolysis process. Furthermore, the lack of chloride ion complexation made copper unstable in the electrolyte, resulting in a large amount of copper oxide impurities in the cathode recovered, reducing the purity of the cathode recovered copper.

[0066] Comparative Example 5 Compared with Example 1, the only difference is that in step (2), the current density is 0 mA / cm 2 .

[0067] The extraction rate of copper from waste CPU in this comparative example is 42.7%, and no copper element is obtained at the cathode. The reason is that the current density in this comparative example is 0 mA / cm 2 There is no external electric field to provide oxidation ability at the anode, and the copper in the discarded CPU is formed by Cu in the electrolyte. 2+ It is oxidized together with dissolved oxygen, and the extraction rate is low; at the same time, there is no external electric field to provide reducing ability at the cathode, the copper ions in the solution will not be reduced, and the cathode cannot obtain copper element.

[0068] In summary, the present invention does not need to adopt the four-step process of gold leaching-extraction-strip extraction-reduction, and directly obtains gold from electronic waste in the form of gold foil, shortening the process of extracting gold from electronic waste. At the same time, the valence state of gold does not change in the extraction process, and gold in elemental form can be directly obtained, avoiding the loss of gold in a long process, and the gold recovery rate is high; the present invention does not leach gold, and does not need to use highly toxic and highly corrosive agents such as aqua regia and cyanide. The agents used in the present invention are simple, easy to handle, and have good environmental benefits; the present invention adopts a slurry electrolysis method to combine the copper leaching and recovery processes, and can directly extract copper from electronic waste in one step, shortening the copper extraction process, and the obtained copper has high purity.

[0069] The specific embodiments of the present invention described above do not limit the scope of protection of the present invention. Any other corresponding changes and modifications made based on the technical concept of the present invention should be included in the scope of protection of the claims of the present invention.

Claims

1. A method for electrochemical cascade extraction of gold and copper from electronic waste, characterized in that: The following steps are involved: A mixed solution of sulfuric acid and copper sulfate is used as the first electrolyte, and the electronic waste is used as the anode to carry out a first electrolysis reaction. The electronic waste after gold removal is then taken out, and the anode chamber solution is subjected to solid-liquid separation and dried to obtain gold foil. A mixed solution of sodium chloride, sulfuric acid, copper sulfate and diethylenetriaminepentaacetic acid is used as the second electrolyte, and the electronic waste after gold removal is added to the anode chamber to perform a second electrolysis reaction, and then the sediment in the cathode chamber is collected, passivated, cleaned and dried to obtain copper foil; wherein, In the first electrolyte, the concentration of sulfuric acid is 0.05-0.25 mol / L, and the concentration of copper sulfate pentahydrate is 5-50 mmol / L; In the second electrolyte, the concentration of sodium chloride is 0.4-1.6 mol / L, the concentration of sulfuric acid is 0.05-0.5 mol / L, the concentration of copper sulfate pentahydrate is 20-100 mmol / L, and the concentration of diethylenetriaminepentaacetic acid is 5-30 mmol / L.

2. The method for electrochemical cascade extraction of gold and copper from electronic waste according to claim 1, characterized in that: The electronic waste is printed circuit board type electronic waste.

3. The method for electrochemical cascade extraction of gold and copper from electronic waste according to claim 1, characterized in that: During the first electrolysis reaction, the cathode is one of a titanium plate, a stainless steel plate, and a copper plate; and the diaphragm is an acid-resistant filter mesh with a pore size of 25-75 μm.

4. The method for electrochemical cascade extraction of gold and copper from electronic waste according to claim 1, characterized in that: During the first electrolysis reaction, the voltage is 0.8-2.5 V, the electrolysis time is 6-24 h, the electrolysis temperature is 15-45° C., and the stirring speed of the anode chamber is 100-500 r / min.

5. The electrochemical cascade extraction method for gold and copper from electronic waste according to claim 1, characterized in that: During the second electrolytic reaction, the electronic waste after gold removal is pre-crushed to a particle size of 100-1000 μm, and then cleaned and dried.

6. The method for electrochemical cascade extraction of gold and copper from electronic waste according to claim 1, characterized in that: During the second electrolysis reaction, the diaphragm is an acid-resistant filter mesh with a pore size of 50-100 μm; the anode is one of a graphite plate, titanium-based lead dioxide, an iridium-plated tantalum titanium plate, and an iridium-plated tantalum titanium mesh; and the cathode is one of a titanium plate, a stainless steel plate, and a copper plate.

7. The method for electrochemical cascade extraction of gold and copper from electronic waste according to claim 1, characterized in that: During the second electrolysis reaction, the content of the gold-removed electronic waste in the second electrolyte is 40-200 g / L.

8. The method for electrochemical cascade extraction of gold and copper from electronic waste according to claim 1, characterized in that: During the second electrolysis reaction, the current density is 5-50 mA / cm 2 , electrolysis time is 8-24 h, electrolysis temperature is 15-45℃, and stirring speed of the anode chamber is 200-500 r / min.

9. The method for electrochemical cascade extraction of gold and copper from electronic waste according to claim 1, characterized in that: In the first electrolyte, the concentration of sulfuric acid is 0.1 mol / L, and the concentration of copper sulfate pentahydrate is 30-50 mmol / L; In the second electrolyte, the concentration of sodium chloride is 1.2-1.6 mol / L, the concentration of sulfuric acid is 0.15-0.5 mol / L, the concentration of copper sulfate pentahydrate is 60-100 mmol / L, and the concentration of diethylenetriaminepentaacetic acid is 10-20 mmol / L.

10. The method for electrochemical cascade extraction of gold and copper from electronic waste according to claim 1, characterized in that: Passivation is carried out by soaking in benzotriazole solution; wherein, The concentration of the benzotriazole solution is 2-10 g / L; the soaking temperature is room temperature; and the soaking time is 2-10 min.

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