Selective leaching method for copper in waste circuit board

Abstract

The invention relates to the technical field of waste metal recovery, and particularly provides a selective leaching method for copper in a waste circuit board, which comprises the following steps: mixing a pretreated waste circuit board raw material with a methanesulfonic acid solution, setting a first reaction temperature, and adding a strong oxidant and a metal inhibitor for reaction, and after the reaction is finished, setting a second reaction temperature to continue the reaction, and after the reaction is finished, separating to obtain a copper-rich leaching solution and leaching residues. According to the method, a leaching system is precisely regulated and controlled, so that target metal enters a solution phase, other impurity metal is enriched in leaching residues in a precipitation form, and efficient selective leaching of copper is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of waste metal recycling, and particularly relates to a method for selectively leaching copper from waste printed circuit boards. Background Art

[0002] Driven by the dual acceleration of technological iteration and the upgrade of consumption patterns, the replacement cycle of electronic products has been significantly shortened, leading to a continuous increase in the pressure of e-waste treatment. Statistical data shows that the annual global output of e-waste has exceeded 60 million tons and maintains an average annual growth rate of 3% - 5%. It is expected that the total amount will climb to more than 74 million tons by 2030.

[0003] As one of the main types of e-waste, waste printed circuit boards 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 in them is generally higher than that of primary mineral resources. It should be emphasized that 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 not properly disposed of, posing a double threat to the ecological environment and public health.

[0004] Current mainstream recycling technologies for waste printed circuit boards include physical methods, pyrometallurgy, hydrometallurgy, and biological methods, etc. The physical method realizes the primary separation of metals and non-metals through pretreatment processes such as mechanical crushing and air classification, and has the advantages of simple process and low energy consumption. It 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: although excessive crushing can improve the metal exposure rate to increase the recovery rate, it will generate micron-sized metal-non-metal mixed dust, resulting in a decrease in metal capture efficiency and an increase in material loss, seriously affecting the economy of subsequent enrichment processes.

[0005] Pyrometallurgical recycling technology has the advantages of large treatment scale and strong process adaptability, and is particularly suitable for the industrial recycling of copper. After pre-roasting to remove organic matter, the obtained metal-rich aggregate can be directly incorporated into the copper smelting system to co-produce blister copper with copper concentrate. Although the pyrometallurgical process is widely used, there are still two core bottlenecks: firstly, the process depends on fossil fuels as heat sources and reducing agents, and the high-temperature cracking of non-metal components such as epoxy resins leads to the emission of a large amount of greenhouse gases such as carbon dioxide, conflicting with the low-carbon transformation goal of the smelting industry; secondly, the generation of toxic by-products such as dioxins and heavy metal vapors requires the configuration of complex gas purification systems, which not only increases environmental risks but also significantly raises operating costs.

[0006] Emerging technologies such as biohydrometallurgy and supercritical fluid extraction provide new paths for green recycling. Biohydrometallurgy uses microorganisms such as sulfur-oxidizing bacteria to metabolize and produce acids to achieve selective leaching of metals, but it is limited by the strict requirements of bacterial activity for environmental parameters; although supercritical technology can achieve efficient separation, it relies on special working conditions of high pressure and high temperature. Currently, most of these innovative processes are in the transition stage from laboratory to pilot scale, and key technical bottlenecks still need to be broken through for large-scale industrial applications.

[0007] Wet processes include key processes such as leaching, solution purification, and electrolytic refining, among which leaching is the core step. Traditional processes mostly 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 cyanides are specifically used for the extraction of precious metals (gold, silver, palladium, etc.). This method has advantages such as mild reaction conditions and wide raw material adaptability, and is suitable for industrial production. It is currently the mainstream process for industrial metal recycling.

[0008] Existing wet processes for treating waste printed circuit boards still have technical problems of poor system selectivity and low leaching efficiency, which greatly limit their industrial application and promotion. Summary of the Invention

[0009] Aiming at the technical problems of poor selectivity and low leaching efficiency of the traditional leaching system in the treatment of waste printed circuit boards mentioned in the background technology, the present invention provides a method for selectively leaching copper from waste printed circuit boards, precisely regulating the leaching system to enable the target metal to enter the solution phase, while other impurity metals are enriched in the leaching residue in the form of precipitates, achieving efficient selective leaching of copper.

[0010] Technical Solution: A method for selectively leaching copper from waste printed circuit boards includes the following steps: mixing the pretreated waste printed circuit board raw materials with a methylsulfonic acid solution, setting a first reaction temperature and adding a strong oxidant and a metal inhibitor for reaction, setting a second reaction temperature after the reaction ends and continuing the reaction, and separating to obtain a copper-rich leaching solution and a leaching residue after the reaction ends.

[0011] Inventive Concept: The inventors of the present application have conducted in-depth research on the problem of difficult selective extraction of copper metal in current waste printed circuit boards. It is found that after introducing strong oxidizing substances to react with the metals in the waste printed circuit boards, high-valent oxides of other metals except copper form insoluble precipitates with methylsulfonic acid, enabling the preliminary separation of copper from other metals. And, by adding a metal inhibitor with a coordinating negative ion and maintaining a relatively low temperature state, it is found that other metal ions can form insoluble compounds and precipitate with the coordinating negative ion while copper oxides still remain in a dissolved state, thereby achieving efficient selective leaching and separation of copper ions.

[0012] Further, the pretreatment includes crushing and grinding, and the particle size of the raw materials < 10 mm.

[0013] Further, 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.

[0014] Further, the first reaction temperature is lower than the second reaction temperature; the first reaction temperature is 30 - 80 °C, and the reaction time is 30 - 120 min; the second reaction temperature is 85 - 120 °C, and the reaction time is 20 - 180 min.

[0015] Further, the strong oxidant includes at least one of a gaseous oxidant and a liquid oxidant; the gaseous oxidant is at least one of chlorine gas and ozone, and the liquid oxidant is at least one of a hydrogen peroxide solution and a nitric acid solution.

[0016] Further, the feeding rate of the gaseous oxidant is 5 - 100 m 3 / h per unit volume of the leaching solution, and the addition amount of the liquid oxidant is 1 - 200 mL per unit volume of the leaching solution.

[0017] Further, the metal inhibitor is an anionic compound capable of forming a complex with the metal, including at least one of phosphates, thiosulfates, oxalates, and citrates; the phosphates, thiosulfates, oxalates, and citrates are salts compatible with methanesulfonic acid, and are selected from at least one of alkali metal salts, alkaline earth metal salts, and ammonium salts.

[0018] Further, the addition amount of the metal inhibitor is 0.1 - 50 g / L.

[0019] Further, the total concentration of non-copper impurity metal ions in the copper-rich leaching solution is < 0.2 g / L, and the concentration of a single non-copper impurity metal ion is < 0.05 g / L.

[0020] Advantages of the present invention: 1. By precisely regulating the leaching system, the target metal enters the solution phase, while other impurity metals are enriched in the leaching residue in the form of precipitation, realizing the efficient selective dissolution of copper, effectively reducing the difficulty of subsequent solution purification, and promoting the staged and gradient recovery of valuable metals. The present invention can simultaneously optimize the leaching energy consumption and control the three-waste emissions, and has both environmental friendliness and economic feasibility.

[0021] 2. The applicant of this application found that the gradient temperature-controlled reaction process can significantly improve the kinetic selectivity of copper leaching. In the low-temperature stage, non-copper metals and the coordination negative ion inhibitor form an insoluble complex through the coordination-precipitation coupling mechanism; while in the high-temperature stage, copper oxide preferentially undergoes a chelation dissolution reaction with methanesulfonic acid, and other metals are retained in the solid phase in the form of insoluble salts due to the difference in thermodynamic stability. This dual-temperature zone synergistic mechanism improves the selectivity of copper leaching.

[0022] 3. The inventor of this application found that the metal inhibitor with coordination negative ions has a specific inhibitory effect on non-copper metals in the methanesulfonic acid system. Through selective coordination, this inhibitor promotes the precipitation phase change of dissolved non-copper metal ions, and finally enriches them in the leaching residue in a targeted manner, realizing the efficient separation of copper and non-copper metals. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a statistical chart of the experimental results in Experimental Example 1 of the present invention; Figure 2 It is a statistical chart of the experimental results in Experimental Example 2 of the present invention; Figure 3 It is a statistical chart of the experimental results in Experimental Example 2 of the present invention; Figure 4 It is a physical picture of the copper-rich leaching solution in Embodiment 1 of the present invention; Figure 5 It is an XRD pattern of the raw materials and leaching residue in Embodiment 1 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0024] The specific embodiments of the present invention will be described in detail below with reference to the specific drawings. It should be noted that the technical features described in the following embodiments or the combination of technical features should not be considered isolated, and they can be combined with each other to achieve better technical effects.

[0025] The present invention provides a method for selectively leaching copper from waste printed circuit boards, including the following steps: mixing the pretreated waste printed circuit board raw materials with a methanesulfonic acid solution, setting the first reaction temperature and adding a strong oxidant and a metal inhibitor to react, setting the second reaction temperature to continue the reaction after the reaction ends, and separating to obtain a copper-rich leaching solution and a leaching residue after the reaction ends.

[0026] Among them, the waste printed circuit boards come from various recyclable circuit boards, such as electronic products like computer devices, calculators, game consoles, etc. The recycled waste printed circuit boards need to be pretreated by crushing and grinding to facilitate the full contact between the metal materials in the circuit boards and the reaction solution. The pretreated waste printed circuit board raw materials are granular powders smaller than 10 mm, and preferably granular powders smaller than 5 mm to improve the reaction effect and rate.

[0027] In the present invention, the methanesulfonic acid solution is purchased from Shandong Yukang Chemical Co., Ltd. and has a concentration of 0.5 - 5 mol / L during use, preferably 2 - 4 mol / L. The solid-liquid ratio of the methanesulfonic acid solution usage amount to the waste circuit board raw material is 1:5 - 20, preferably 1:8 - 15.

[0028] In the present invention, the strong oxidant is at least one of a gaseous oxidant and a liquid oxidant, and a liquid oxidant is preferably used for simplifying the reaction device. Among them, the gaseous oxidant is at least one of chlorine gas and ozone, and the feeding rate is 0.1 - 1.5 L / min per liter of leaching solution, preferably 0.5 - 1 L / min. The liquid oxidant is at least one of hydrogen peroxide and nitric acid solution, and the addition amount is 1 - 200 mL added per liter of leaching solution, preferably 10 - 100 mL. The above-mentioned strong oxidants are all commercially available products without special requirements.

[0029] In the present invention, the metal inhibitor is an anionic compound that can form a complex with metals. The metal inhibitor has a specific inhibitory effect on non-copper metals in the methanesulfonic acid system. Through selective coordination, it promotes the precipitation phase change of dissolved non-copper metal ions, and finally enriches them in the leaching residue in a targeted manner, realizing the efficient separation of copper and non-copper metals.

[0030] The metal inhibitor is selected from at least one of phosphates, thiosulfates, oxalates, and citrates, and the addition amount is 0.1 - 50 g / L, preferably 5 - 20 g / L. Phosphates, thiosulfates, oxalates, and citrates are salts compatible with the methanesulfonic acid system and are selected from at least one of alkali metal salts, alkaline earth metal salts, and ammonium salts, and further preferably alkali metal phosphates. The above-mentioned metal inhibitors can all be commercially available products without special regulations.

[0031] The present invention adopts a gradient temperature control reaction process, setting a first reaction temperature and a second reaction temperature, where the first reaction temperature is lower than the second reaction temperature. In this way, in the low-temperature stage of the first reaction, non-copper metals and the coordination negative ion inhibitor form an insoluble complex through a coordination-precipitation coupling mechanism, while in the high-temperature stage of the second reaction, copper oxide preferentially undergoes a chelation dissolution reaction with methanesulfonic acid, and other metals are retained in the solid phase in the form of insoluble salts due to differences in thermodynamic stability. This gradient temperature control reaction process improves the selectivity of copper leaching.

[0032] In the present invention, the first reaction temperature is 30 - 80 °C, further preferably 40 - 50 °C, the reaction time is 30 - 120 min, further preferably 40 - 80 min; the second reaction temperature is 85 - 120 °C, further preferably 85 - 100 °C, and the reaction time is 20 - 180 min, further preferably 30 - 100 min.

[0033] Example 1 This embodiment provides a method for selectively leaching copper from waste printed circuit boards, which includes the following steps: Take 100 g of waste printed circuit boards, crush, grind them, and sieve to obtain raw materials with a size less than 5 mm. Among them, the copper content in the waste printed circuit boards is 14.6%, the tin content is 5.6%, the iron content is 4.8%, the lead content is 3.0%, the nickel content is 1.7%, the silver content is 0.05%, and the gold content is 0.02%. Add the raw materials into a methanesulfonic acid solution with a concentration of 4 mol / L, control the solid-liquid ratio of the raw materials to the methanesulfonic acid solution to be 1:15, then set the first reaction temperature to 50 °C and add 150 mL of hydrogen peroxide and 20 g of sodium phosphate, after reacting for 80 min, set the second reaction temperature to 100 °C and continue to react for 100 min. After the reaction is completed, solid-liquid separation is carried out to obtain a copper-rich leaching solution and leaching residues. The copper-rich leaching solution is as shown in Figure 4 shown, and the XRD pattern of the leaching residues is as shown in Figure 5 shown. Using the ICP-OES combined with XRF method, the concentrations of various metal ions in the leaching solution and the contents of various metal elements in the leaching residues are detected. It can be analyzed that the leaching rate of copper is 98.55%, the copper concentration in the solution is 8.7 g / L, and the concentrations of other metals do not exceed 0.02 g / L.

[0034] Example 2 The difference between this embodiment and Example 1 lies in the different reaction conditions. Specifically: Take 100 g of the same waste printed circuit boards as used in Example 1, crush and grind them to obtain raw materials with a size less than 10 mm, add them into a methanesulfonic acid solution with a concentration of 0.5 mol / L, control the solid-liquid ratio of the raw materials to the methanesulfonic acid solution to be 1:5, then set the first reaction temperature to 30 °C and introduce ozone gas with a gas flow rate of 0.3 L / min and add 0.05 g of sodium oxalate, after reacting for 30 min, set the second reaction temperature to 80 °C and react for 20 min. After the reaction is completed, solid-liquid separation is carried out to obtain a copper-rich leaching solution and leaching residues. Using the ICP-OES combined with XRF method, the concentrations of various metal ions in the leaching solution and the contents of various metal elements in the leaching residues are detected. It can be analyzed that the leaching rate of copper is 92.64%, the copper concentration in the solution is 27.1 g / L, and the concentrations of other metals do not exceed 0.05 g / L.

[0035] Example 3 The difference between this example and Example 1 lies in the waste printed circuit boards and reaction conditions. Specifically, 100 g of waste printed circuit boards were taken, crushed and ground to obtain raw materials with a size less than 10 mm. Among them, the copper content in the waste printed circuit boards was 10.5%, the tin content was 6.7%, the iron content was 7.8%, the lead content was 4.2%, the nickel content was 0.7%, the silver content was 0.02%, and the gold content was 0.01%. It was added to a methylsulfonic acid solution with a concentration of 5 mol / L, and the solid-liquid ratio of the raw materials to the methylsulfonic acid solution was controlled at 1:10. The first reaction temperature was 40 °C, 100 mL of hydrogen peroxide and 10 g of sodium phosphate were added, and after reacting for 60 min, the second reaction temperature was set at 90 °C and the reaction continued for 90 min. After the reaction ended, solid-liquid separation was carried out to obtain a copper-rich leaching solution and a leaching residue. The ICP-OES combined with XRF method was used to detect the concentrations of various metal ions in the leaching solution and the contents of various metal elements in the leaching residue. Analysis showed that the leaching rate of copper 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.

[0036] Comparative Example 1 The difference between this comparative example and Example 1 lies in that oxygen was used for the reaction instead of a strong oxidizing substance, the oxygen flow rate was 1 L / min, and other steps and reaction conditions were the same as those in Example 1. The ICP-OES combined with XRF method was used to detect the concentrations of various metal ions in the leaching solution and the contents of various metal elements in the leaching residue. Analysis showed that the leaching rate of copper was 78.5%, the copper concentration in the solution was 7.6 g / L, and the highest-concentration other metal element in the solution was tin, reaching 2.4 g / L.

[0037] Comparative Example 2 The difference between this comparison and Example 1 lies in that the reaction was carried out without adding a coordination negative ion metal inhibitor, and other steps and reaction conditions were the same as those in Example 1. The ICP-OES combined with XRF method was used to detect the concentrations of various metal ions in the leaching solution and the contents of various metal elements in the leaching residue. Analysis showed that the leaching rate of copper was 98.73%, the copper concentration in the solution was 9.2 g / L, and the highest-concentration other metal element in the solution was tin, reaching 1.7 g / L.

[0038] Comparative Example 3 The difference between this comparative example and Example 1 is that the reaction is not carried out using the gradient temperature control process. The reaction temperature is set at 50 °C and the time is 180 min. Other steps and reaction conditions are the same as those in Example 1. After the reaction is completed, solid-liquid separation is carried out to obtain the leaching solution and the leaching residue. The ICP-OES combined with XRF method is used to detect the concentrations of various metal ions in the leaching solution and the contents of various metal elements in the leaching residue. Analysis shows that the leaching rate of copper is 98.25%, the concentration of copper in the solution is 9.2 g / L, and the highest concentration of other metal elements in the solution is tin, reaching 0.5 g / L.

[0039] Comparative Example 4 The difference between this comparative example and Example 1 is that neither the coordination negative ion metal inhibitor is added for the reaction nor the gradient temperature control process is adopted. The reaction temperature is set at 50 °C and the time is 180 min. Other steps and reaction conditions are the same as those in Example 1. After the reaction is completed, solid-liquid separation is carried out to obtain the leaching solution and the leaching residue. The ICP-OES combined with XRF method is used to detect the concentrations of various metal ions in the leaching solution and the contents of various metal elements in the leaching residue. Analysis shows that the leaching rate of copper is 98.01%, the concentration of copper in the solution is 9.1 g / L, and the highest concentration of other metal elements in the solution is tin, reaching 2.1 g / L.

[0040] Experimental Example 1 Experimental purpose: To explore the effect of the concentration of the metal inhibitor on the selective leaching of copper Experimental method: According to the reaction steps and reaction conditions of Example 1, five groups of experiments with the metal inhibitor dosages of 0, 5 g / L, 10 g / L, 20 g / L, and 50 g / L are set. Finally, the highest concentration of other metal elements except copper in the solution is represented by the elemental content analysis, and the results are as follows Figure 1 shown.

[0041] Analysis of experimental results: As the dosage of the metal inhibitor increases, the concentrations of other metal elements except copper in the solution show a trend of first decreasing significantly and then gradually stabilizing. When no metal inhibitor is used, a small amount of tin reacts with the leaching agent and dissolves into the solution, and it is difficult to precipitate, and the concentration exceeds 1.6 g / L. When the dosage of the metal inhibitor reaches 20 g / L, the tin in the solution basically completely reacts with it to form insoluble or slightly soluble compounds and then precipitates. At this time, the concentration of tin in the solution is close to 0. It is worth mentioning that as the concentration of the metal inhibitor gradually increases, the leaching rate of copper shows a trend of first increasing and then decreasing. This is because the excessive addition of the metal inhibitor changes the physical properties of the solution, increases the viscosity of the solution, reduces the fluidity, and makes it more difficult for copper to be leached.

[0042] Experimental Example 2 Experimental purpose: To explore the effect of the reaction temperature on the selective leaching of copper Experimental method: According to the reaction steps and reaction conditions of Example 1, set the first reaction temperatures to 30 °C, 40 °C, 50 °C, 60 °C, 70 °C, and 80 °C respectively, fix the second reaction temperature at 100 °C, and set up six groups of experiments. Finally, represent the highest concentration of other metal elements except copper in the solution through elemental content analysis. The results are as shown in the appendix Figure 2 as follows.

[0043] In addition, determine the first reaction temperature to be 50 °C, and the second reaction temperatures to be 80 °C, 90 °C, 100 °C, 110 °C, and 120 °C respectively. Set up five groups of experiments. Finally, represent the highest concentration of other metal elements except copper in the solution through elemental content analysis. The results are as shown in the appendix Figure 3 as follows.

[0044] Analysis of experimental results: Changing the first reaction temperature has a certain impact on both the leaching rate of copper and the concentration of other metal elements except copper in the solution. As the first reaction temperature increases, the concentration of other metal elements except copper in the solution shows a trend of first decreasing, then remaining stable, and then increasing. The leaching rate of copper also shows a trend of first increasing and then decreasing. This is because the increase in temperature causes the decomposition rate of hydrogen peroxide oxidant to increase, and the amount of metal oxidized and leached decreases. Changing the second reaction temperature has not much impact on the leaching rate of copper and the concentration of other metal elements except copper in the solution, but the concentration of impurity ions still shows a trend of decreasing and gradually stabilizing.

[0045] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and can be implemented in other specific forms without departing from the spirit or basic characteristics of the present invention. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. In addition, it should be understood that although this specification is described according to the implementation manners, it does not only include one technical solution. This narrative manner of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in the embodiments can also be appropriately combined to form other implementation manners that can be understood by those skilled in the art.

Claims

1. A method for selectively leaching copper from waste printed circuit boards, characterized in that, It includes the following steps: Mix the pretreated waste circuit board raw materials with a methanesulfonic acid solution, set the first reaction temperature, add a strong oxidant and a metal inhibitor for reaction, and after the reaction ends, set the second reaction temperature to continue the reaction. After the reaction ends, separate to obtain a copper-rich leaching solution and leaching residues.

2. The selective leaching method of copper in waste printed circuit boards according to claim 1, characterized in that, The pretreatment includes crushing and grinding, and the particle size of the raw materials is < 10 mm.

3. The selective leaching method of 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 materials to the methanesulfonic acid solution is 1:5 - 20.

4. A method for selectively leaching copper from waste printed 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 °C, and the reaction time is 30 - 120 min; the second reaction temperature is 85 - 120 °C, and the reaction time is 20 - 180 min.

5. The selective leaching method of copper in waste printed 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 gas and ozone, and the liquid oxidant is at least one of a hydrogen peroxide solution and a nitric acid solution.

6. The preparation method of the selective leaching method of copper in waste circuit boards according to claim 5, characterized in that, The feeding rate of the gaseous oxidant is 0.1 - 1.5 L / min per liter of the leaching solution by volume, and the addition amount of the liquid oxidant is 1 - 200 mL per unit volume of the leaching solution.

7. The preparation method of the method for selectively leaching copper in waste circuit boards according to claim 1, characterized in that, The metal inhibitor is an anionic compound capable of forming a complex with a metal, including at least one of phosphates, thiosulfates, oxalates, and citrates; the phosphates, thiosulfates, oxalates, and citrates are salts compatible with methanesulfonic acid, selected from at least one of alkali metal salts, alkaline earth metal salts, and ammonium salts.

8. The preparation method of the selective leaching method of copper in waste printed circuit boards according to claim 7, characterized in that, The addition amount of the metal inhibitor is 0.1 - 50 g / L.

9. The preparation method of the selective leaching method of copper in waste circuit boards according to claim 1, characterized in that The total concentration of non-copper impurity metal ions in the copper-rich leaching solution is < 0.2 g / L, and the individual concentration of non-copper impurity metal ions is < 0.05 g / L.

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