A selective leaching method of copper in waste circuit board

Abstract

The present application relates to the technical field of waste metal recycling, and specifically provides a selective leaching method for copper in waste circuit boards, comprising the following steps: mixing pretreated waste circuit board raw materials with a methyl sulfonic acid solution, setting a first reaction temperature and adding a strong oxidizing agent and a metal inhibitor for reaction, continuing the reaction at a second reaction temperature after the reaction is completed, and separating to obtain a copper-rich leaching solution and a leaching residue. The present application realizes efficient and selective leaching of copper by precisely controlling the leaching system, so that the target metal enters the solution phase, and other impurity metals are enriched in the leaching residue in the form of precipitation.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of waste metal recycling, and particularly relates to a selective leaching method of copper in waste circuit boards. BACKGROUND

[0002] Under the dual driving of accelerated technology iteration and upgraded consumption mode, the replacement cycle of electronic products has been significantly shortened, which has triggered the increasing pressure of electronic waste management. Statistics show that the global annual output of electronic waste has broken through the 6000-ton threshold, with an annual growth rate of 3%-5%, and is expected to climb to more than 7400 tons by 2030.

[0003] Waste circuit boards, as one of the main electronic wastes, are rich in high-value metals such as copper and gold, as well as composite materials such as plastics and glass fibers. It is worth noting that the metal content is generally higher than the grade of primary mineral resources. It is particularly important to note that the toxic components such as lead, cadmium, and brominated flame retardants contained in waste circuit boards may cause irreversible pollution of the soil-water system through leaching if improperly disposed, posing a dual threat to the ecological environment and public health.

[0004] The current mainstream recycling technologies for waste circuit boards include physical method, pyrometallurgical method, hydrometallurgical method, and biological method. The physical method realizes the primary separation of metals and non-metals through mechanical crushing, air separation, and other pretreatment processes, with the advantages of simple process and low energy consumption, and is often used as the front-end process for large-scale treatment. However, this technology faces the contradictory relationship between metal dissociation degree and particle size distribution: excessive crushing can increase the exposure rate of metals to improve the recovery rate, but it will produce micron-sized metal-non-metal mixed dust, leading to decreased metal capture efficiency and increased material loss, which seriously affects the economy of the subsequent enrichment process.

[0005] Pyrometallurgical recycling technology has the advantages of large processing capacity and strong process adaptability, and is particularly suitable for industrialized recovery of copper. After pre-roasting to remove organic matter, the obtained metal-rich body can be directly incorporated into the copper smelting system and cooperated with copper concentrate to produce crude copper. Although the pyrometallurgical process is widely used, there are still two major bottlenecks: first, the process relies on fossil fuels as heat source and reducing agent, and the high-temperature cracking of non-metallic components such as epoxy resin leads to the emission of a large amount of greenhouse gases such as carbon dioxide, which conflicts with the low-carbon transformation goal of the smelting industry; second, the generation of toxic by-products such as dioxin and heavy metal vapor requires a complex gas purification system, which not only increases environmental risks but also significantly increases operating costs.

[0006] Emerging technologies such as biometallurgy and supercritical fluid extraction offer new pathways for green recycling. Biometallurgy utilizes the metabolic acid production of microorganisms such as sulfur-oxidizing bacteria to achieve selective metal leaching, but its effectiveness is limited by the stringent environmental parameters required for bacterial activity. While supercritical technology can achieve highly efficient separation, it relies on specific high-pressure and high-temperature operating conditions. Currently, these innovative processes are mostly in the transition stage from laboratory to pilot-scale testing, and key technological bottlenecks still need to be overcome before large-scale industrial application.

[0007] Hydrometallurgical processes include key steps such as leaching, solution purification, and electrolytic refining, with leaching being the core step. Traditional processes often use strong inorganic acid systems such as nitric acid and hydrochloric acid to leach base metals (copper, lead, tin, etc.), while highly toxic systems such as cyanide are specifically used for extracting precious metals (gold, silver, palladium, etc.). This method has advantages such as mild reaction conditions and wide adaptability to raw materials, making it suitable for industrial production and currently the mainstream process for industrial metal recovery.

[0008] Existing wet processing methods for treating waste circuit boards still suffer from poor system selectivity and low leaching efficiency, which greatly limits their industrial application and promotion. Summary of the Invention

[0009] In view of the technical problems of poor selectivity and low leaching efficiency in traditional leaching systems for the treatment of waste circuit boards mentioned in the background art, the present invention provides a selective leaching method for copper in waste circuit boards. The leaching system is precisely controlled so that the target metal enters the solution phase, while other impurity metals are enriched in the leaching residue in the form of precipitate, thereby achieving efficient and selective leaching of copper.

[0010] Technical solution:

[0011] A selective leaching method for copper from waste circuit boards includes the following steps: mixing pretreated waste circuit board raw materials with methanesulfonic acid solution, setting a first reaction temperature and adding a strong oxidant and a metal inhibitor to react, setting a second reaction temperature to continue the reaction after the reaction is completed, and separating copper-rich leachate and leaching residue after the reaction is completed.

[0012] Inventive concept:

[0013] The inventors of this application have conducted in-depth research on the difficulty of selectively extracting copper from waste circuit boards. They discovered that by introducing a strong oxidizing agent to react with the metals in the waste circuit boards, the high-valence oxides of other metals besides copper form insoluble precipitates with methanesulfonic acid, achieving preliminary separation of copper from other metals. Furthermore, by adding a metal inhibitor containing coordinating anions and maintaining a relatively low temperature, they found that other metal ions can form insoluble compound precipitates with the coordinating anions, while copper oxides remain dissolved, thus achieving highly efficient and selective leaching and separation of copper ions.

[0014] Furthermore, the pretreatment includes crushing and grinding, wherein the raw material particle size is <10 mm.

[0015] Furthermore, the concentration of the methanesulfonic acid solution is 0.5~5 mol / L, and the solid-liquid ratio of the raw material to the methanesulfonic acid solution is 1:5~20.

[0016] Furthermore, the first reaction temperature is lower than the second reaction temperature; the first reaction temperature is 30~80 ℃, and the reaction time is 30~120 min; the second reaction temperature is 85~120 ℃, and the reaction time is 20~180 min.

[0017] Furthermore, the strong oxidant includes at least one of a gaseous oxidant and a liquid oxidant; the gaseous oxidant is at least one of chlorine and ozone, and the liquid oxidant is at least one of hydrogen peroxide solution and nitric acid solution.

[0018] Furthermore, the gaseous oxidant is introduced at a rate of 5-100 m³ / unit of leaching solution. 3 / h, wherein the amount of liquid oxidant added is 1~200 mL per unit volume of leaching solution.

[0019] Furthermore, the metal inhibitor is an anionic compound capable of forming a complex with a metal, including at least one of phosphate, thiosulfate, oxalate, and citrate; the phosphate, thiosulfate, oxalate, and citrate are salts compatible with methanesulfonic acid, selected from at least one of alkali metal salts, alkaline earth metal salts, and ammonium salts.

[0020] Furthermore, the amount of metal inhibitor added is 0.1~50 g / L.

[0021] Furthermore, the total concentration of non-copper impurity metal ions in the copper-rich leachate is <0.2 g / L, and the concentration of a single non-copper impurity metal ion is <0.05 g / L.

[0022] The beneficial effects of this invention are:

[0023] 1. This invention achieves highly efficient and selective dissolution of copper by precisely controlling the leaching system, allowing the target metal to enter the solution phase while other impurity metals precipitate and accumulate in the leaching residue. This effectively reduces the difficulty of subsequent solution purification and promotes the phased, gradient recovery of valuable metals. This invention simultaneously optimizes leaching energy consumption and controls waste emissions, combining environmental friendliness with economic feasibility.

[0024] 2. The applicants of this application have discovered that gradient temperature-controlled reaction processes can significantly improve the kinetic selectivity of copper leaching. In the low-temperature stage, non-copper metals and coordination anion inhibitors form insoluble complexes through a coordination-precipitation coupling mechanism; while in the high-temperature stage, copper oxides preferentially undergo chelation dissolution reactions with methanesulfonic acid, and other metals are retained in the solid phase as insoluble salts due to differences in thermodynamic stability. This dual-temperature-zone synergistic mechanism improves the leaching selectivity of copper.

[0025] 3. The inventors of this application have discovered that metal inhibitors with coordinating anions have a specific inhibitory effect on non-copper metals in a methanesulfonic acid system. This inhibitor, through selective coordination, promotes the precipitation phase transition of dissolved non-copper metal ions, ultimately leading to their directional enrichment in the leaching residue, thus achieving efficient separation of copper and non-copper metals. Attached Figure Description

[0026] Figure 1 This is a statistical graph of the experimental results in Experiment Example 1 of this invention;

[0027] Figure 2 This is a statistical graph of the experimental results in Experiment Example 2 of the present invention;

[0028] Figure 3 This is a statistical graph of the experimental results in Experiment Example 2 of the present invention;

[0029] Figure 4 This is a photograph of the copper-rich leaching solution in Example 1 of the present invention;

[0030] Figure 5 The image shows the XRD patterns of the raw materials and leaching residue in Example 1 of this invention. Detailed Implementation

[0031] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be noted that the technical features or combinations of technical features described in the following embodiments should not be considered in isolation, but can be combined with each other to achieve better technical effects.

[0032] This invention provides a selective leaching method for copper from waste circuit boards, comprising the following steps: mixing pretreated waste circuit board raw materials with methanesulfonic acid solution, setting a first reaction temperature and adding a strong oxidant and a metal inhibitor to react, setting a second reaction temperature to continue the reaction after the reaction is completed, and separating copper-rich leachate and leaching residue after the reaction is completed.

[0033] The waste circuit boards come from various recyclable circuit boards, such as those found in computer equipment, calculators, game consoles, and other electronic products. The collected waste circuit boards undergo pre-treatment involving crushing and grinding to ensure sufficient contact between the metal materials in the circuit boards and the reaction solution. The pre-treated waste circuit board raw material is a granular powder smaller than 10mm, but to improve the reaction effect and rate, a granular powder smaller than 5mm is preferred.

[0034] In this invention, the methanesulfonic acid solution was purchased from Shandong Yukang Chemical Co., Ltd., and its concentration was 0.5~5 mol / L, preferably 2~4 mol / L. The solid-liquid ratio of the methanesulfonic acid solution used to the waste circuit board raw material was 1:5~20, preferably 1:8~15.

[0035] In this invention, the strong oxidant is at least one of a gaseous oxidant or a liquid oxidant, with a liquid oxidant preferred for simplifying the reaction apparatus. The gaseous oxidant is at least one of chlorine and ozone, with a flow rate of 0.1–1.5 L / min per liter of leachate, preferably 0.5–1 L / min. The liquid oxidant is at least one of hydrogen peroxide and nitric acid solution, added at a rate of 1–200 mL per liter of leachate, preferably 10–100 mL. All the above-mentioned strong oxidants are commercially available products and have no special requirements.

[0036] In this invention, the metal inhibitor is an anionic compound that can form a complex with a metal. This metal inhibitor has a specific inhibitory effect on non-copper metals in the methanesulfonic acid system. Through selective coordination, it promotes the precipitation phase transition of dissolved non-copper metal ions, which are eventually directionally enriched in the leaching residue, thereby achieving efficient separation of copper and non-copper metals.

[0037] The metal inhibitor is selected from at least one of phosphates, thiosulfates, oxalates, and citrates, and is added in an amount of 0.1–50 g / L, preferably 5–20 g / L. The phosphates, thiosulfates, oxalates, and citrates are methanesulfonic acid-compatible salts, selected from at least one of alkali metal salts, alkaline earth metal salts, and ammonium salts, with alkali metal phosphates being more preferred. All of the above metal inhibitors can be commercially available products, without special requirements.

[0038] This invention employs a gradient temperature-controlled reaction process, setting a first reaction temperature and a second reaction temperature, wherein the first reaction temperature is lower than the second reaction temperature. In this way, during the low-temperature stage of the first reaction, non-copper metals and coordination anion inhibitors form insoluble complexes through coordination-precipitation coupling mechanisms. During the high-temperature stage of the second reaction, copper oxides preferentially undergo chelation dissolution reactions with methanesulfonic acid, while other metals are retained in the solid phase as insoluble salts due to differences in thermodynamic stability. This gradient temperature-controlled reaction process improves the selectivity of copper leaching.

[0039] In this invention, the first reaction temperature is 30~80 ℃, more preferably 40~50 ℃, and the reaction time is 30~120 min, more preferably 40~80 min; the second reaction temperature is 85~120 ℃, more preferably 85~100 ℃, and the reaction time is 20~180 min, more preferably 30~100 min.

[0040] Example 1

[0041] This embodiment provides a method for selective leaching copper from waste circuit boards, comprising the following steps: 100 g of waste circuit boards are crushed, ground, and sieved to obtain raw materials with a size less than 5 mm. The waste circuit boards contain 14.6% copper, 5.6% tin, 4.8% iron, 3.0% lead, 1.7% nickel, 0.05% silver, and 0.02% gold. A 4 mol / L methanesulfonic acid solution is added to the raw materials, controlling the solid-liquid ratio of the raw materials to the methanesulfonic acid solution to be 1:15. The first reaction temperature is then set to 50 °C, and 150 mL of hydrogen peroxide and 20 g of sodium phosphate are added. After reacting for 80 min, the second reaction temperature is set to 100 °C and the reaction continues for another 100 min. After the reaction, solid-liquid separation is performed to obtain a copper-rich leachate and a leaching residue. The copper-rich leachate is shown in the attached figure. Figure 4 The XRD pattern of the leaching residue is shown in the attached figure. Figure 5 As shown in the figure. The concentrations of various metal ions in the leaching solution and the content of various metal elements in the leaching residue were detected by ICP-OES combined with XRF. The analysis showed that the leaching rate of copper was 98.55%, the copper concentration in the solution was 8.7 g / L, and the concentrations of other metals did not exceed 0.02 g / L.

[0042] Example 2

[0043] The difference between this embodiment and Embodiment 1 lies in the reaction conditions. Specifically, 100 g of waste circuit boards, using the same raw materials as in Embodiment 1, were crushed and ground to obtain raw materials with dimensions less than 10 mm. These materials were then added to a 0.5 mol / L methanesulfonic acid solution, with the solid-liquid ratio of the raw materials to the methanesulfonic acid solution controlled at 1:5. Subsequently, the first reaction temperature was set at 30 °C, and ozone gas with a flow rate of 0.3 L / min was introduced, along with 0.05 g of sodium oxalate. After reacting for 30 min, the second reaction temperature was set at 80 °C for 20 min. After the reaction, solid-liquid separation yielded a copper-rich leaching solution and leaching residue. The concentrations of various metal ions in the leaching solution and the content of various metal elements in the leaching residue were detected using ICP-OES combined with XRF. Analysis showed that the copper leaching rate was 92.64%, the copper concentration in the solution was 27.1 g / L, and the concentrations of other metals did not exceed 0.05 g / L.

[0044] Example 3

[0045] The difference between this embodiment and Embodiment 1 lies in the waste circuit board and the reaction conditions. Specifically: 100 g of waste circuit board was crushed and ground to obtain raw material with a size less than 10 mm. The waste circuit board contained 10.5% copper, 6.7% tin, 7.8% iron, 4.2% lead, 0.7% nickel, 0.02% silver, and 0.01% gold. A 5 mol / L methanesulfonic acid solution was added, controlling the solid-liquid ratio of the raw material to the methanesulfonic acid solution to be 1:10. The first reaction temperature was 40 °C, and 100 mL of hydrogen peroxide and 10 g of sodium phosphate were added. After reacting for 60 min, the second reaction temperature was set to 90 °C, and the reaction continued for another 90 min. After the reaction was completed, solid-liquid separation was performed to obtain copper-rich leachate and leaching residue. The concentrations of various metal ions in the leachate and the content of various metal elements in the leaching residue were detected by ICP-OES combined with XRF. The analysis showed that the copper leaching rate was 96.32%, the copper concentration in the solution was 9.2 g / L, and the concentrations of other metals did not exceed 0.04 g / L.

[0046] Comparative Example 1

[0047] The difference between this comparative example and Example 1 is that oxygen was used instead of a strong oxidizing agent for the reaction, with an oxygen flow rate of 1 L / min. Other steps and reaction conditions were the same as in Example 1. The concentrations of various metal ions in the leaching solution and the content of various metal elements in the leaching residue were detected using ICP-OES combined with XRF. Analysis showed that the copper leaching rate was 78.5%, the copper concentration in the solution was 7.6 g / L, and the highest concentration of other metal elements in the solution was tin, reaching 2.4 g / L.

[0048] Comparative Example 2

[0049] The difference between this comparative study and Example 1 is that no coordination anion metal inhibitor was added during the reaction; all other steps and reaction conditions were the same as in Example 1. The concentrations of each metal ion in the leaching solution and the content of each metal element in the leaching residue were detected using ICP-OES combined with XRF. Analysis showed that the copper leaching rate was 98.73%, the copper concentration in the solution was 9.2 g / L, and the highest concentration of other metal element in the solution was tin, reaching 1.7 g / L.

[0050] Comparative Example 3

[0051] The difference between this comparative study and Example 1 is that a gradient temperature control process was not used for the reaction. The reaction temperature was set at 50°C and the time was 180 min. Other steps and reaction conditions were the same as in Example 1. After the reaction, solid-liquid separation was performed to obtain leaching solution and leaching residue. The concentrations of each metal ion in the leaching solution and the content of each metal element in the leaching residue were detected using ICP-OES combined with XRF. The analysis showed that the copper leaching rate was 98.25%, the copper concentration in the solution was 9.2 g / L, and the highest concentration of other metal element in the solution was tin, reaching 0.5 g / L.

[0052] Comparative Example 4

[0053] The difference between this comparative study and Example 1 is that neither the addition of a coordination anion metal inhibitor nor the use of a gradient temperature control process was employed. The reaction temperature was set at 50 °C and the reaction time at 180 min, while the other steps and reaction conditions remained the same as in Example 1. After the reaction, solid-liquid separation was performed to obtain the leachate and leaching residue. The concentrations of each metal ion in the leachate and the content of each metal element in the leaching residue were detected using ICP-OES combined with XRF. Analysis showed that the copper leaching rate was 98.01%, the copper concentration in the solution was 9.1 g / L, and the highest concentration of other metal element in the solution was tin, reaching 2.1 g / L.

[0054] Experimental Example 1

[0055] Experimental objective: To investigate the effect of metal inhibitor concentration on the selective leaching of copper.

[0056] Experimental Methods: Following the reaction steps and conditions of Example 1, five groups of experiments were conducted with metal inhibitor dosages of 0, 5 g / L, 10 g / L, 20 g / L, and 50 g / L. Elemental analysis was used to determine the highest concentrations of all metals except copper in the solution. The results are shown in the appendix. Figure 1 As shown.

[0057] Experimental Results Analysis: With increasing dosage of metal inhibitors, the concentrations of other metal elements in the solution, except for copper, initially decreased significantly, then gradually stabilized. Without metal inhibitors, a small amount of tin reacted with the leaching agent and dissolved into the solution, but it was difficult to precipitate, with a concentration exceeding 1.6 g / L. When the metal inhibitor dosage reached 20 g / L, almost all the tin in the solution reacted with the leaching agent to form insoluble or slightly soluble compounds, which then precipitated, at which point the tin concentration in the solution approached 0. It is worth noting that with gradually increasing metal inhibitor concentrations, the copper leaching rate initially increased and then decreased. This is because excessive metal inhibitors altered the physical properties of the solution, increasing viscosity and reducing fluidity, making copper more difficult to leach.

[0058] Experiment Example 2

[0059] Experimental objective: To investigate the effect of reaction temperature on the selective leaching of copper.

[0060] Experimental Methods: Following the reaction steps and conditions of Example 1, the first reaction temperatures were set at 30 ℃, 40 ℃, 50 ℃, 60 ℃, 70 ℃, and 80 ℃, while the second reaction temperature was fixed at 100 ℃. Six sets of experiments were conducted. Finally, elemental analysis was used to determine the highest concentrations of metals other than copper in the solution. The results are shown in the appendix. Figure 2 As shown.

[0061] In addition, the first reaction temperature was determined to be 50 ℃, and the second reaction temperatures were set at 80 ℃, 90 ℃, 100 ℃, 110 ℃, and 120 ℃, respectively. Five sets of experiments were set up, and the highest concentrations of other metallic elements besides copper in the solution were finally determined by elemental analysis. The results are shown in the appendix. Figure 3 As shown.

[0062] Analysis of experimental results: Changing the first reaction temperature has a certain impact on the leaching rate of copper and the concentration of other metal elements in the solution besides copper. With increasing first reaction temperature, the concentration of other metal elements in the solution first decreases, then stabilizes, and then increases again. The leaching rate of copper also shows a trend of first increasing and then decreasing. This is because the increase in temperature increases the decomposition rate of hydrogen peroxide oxidant, thus reducing the amount of metal leached out by oxidation. Changing the second reaction temperature has little effect on the leaching rate of copper and the concentration of other metal elements in the solution, but the concentration of impurity ions still shows a decreasing and gradually stabilizing trend.

[0063] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered exemplary and not restrictive in all respects. Furthermore, it should be understood that although this specification describes embodiments, it does not encompass only one technical solution. This descriptive method is merely for clarity, and those skilled in the art should consider the specification as a whole. The technical solutions in the embodiments can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for selectively leaching copper from waste circuit boards, characterized in that, Includes the following steps: The pretreated waste circuit board raw materials were mixed with methanesulfonic acid solution, a first reaction temperature was set and a strong oxidant and a metal inhibitor were added to react. After the reaction was completed, a second reaction temperature was set to continue the reaction. After the reaction was completed, copper-rich leachate and leaching residue were separated. The metal inhibitor is an anionic compound that can form a complex with a metal, including at least one of phosphate, thiosulfate, oxalate, and citrate. The amount of metal inhibitor added is 0.1~50 g / L.

2. The selective leaching method for copper from waste circuit boards according to claim 1, characterized in that, The pretreatment includes crushing and grinding, and the raw material has a particle size of <10 mm.

3. The selective leaching method for copper in waste circuit boards according to claim 1, characterized in that, The concentration of the methanesulfonic acid solution is 0.5~5 mol / L, and the solid-liquid ratio of the raw material to the methanesulfonic acid solution is 1:5~20.

4. The selective leaching method for copper from waste circuit boards according to claim 1, characterized in that, The first reaction temperature is lower than the second reaction temperature; the first reaction temperature is 30~80 ℃ and the reaction time is 30~120 min; the second reaction temperature is 85~120 ℃ and the reaction time is 20~180 min.

5. The selective leaching method for copper from waste circuit boards according to claim 1, characterized in that, The strong oxidant includes at least one of a gaseous oxidant and a liquid oxidant; the gaseous oxidant is at least one of chlorine and ozone, and the liquid oxidant is at least one of hydrogen peroxide solution and nitric acid solution.

6. The selective leaching method for copper from waste circuit boards according to claim 5, characterized in that, The gaseous oxidant is introduced at a rate of 0.1 to 1.5 L / min per liter of leachate, and the liquid oxidant is added at a rate of 1 to 200 mL per liter of leachate.

7. The selective leaching method for copper from waste circuit boards according to claim 1, characterized in that, The phosphate, thiosulfate, oxalate, and citrate are salts compatible with methanesulfonic acid and are selected from at least one of alkali metal salts, alkaline earth metal salts, and ammonium salts.

8. The selective leaching method for copper from waste circuit boards according to claim 1, characterized in that, The total concentration of non-copper impurity metal ions in the copper-rich leachate is <0.2 g / L, and the concentration of a single non-copper impurity metal ion is <0.05 g / L.

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