Gluconobacter oxydans for leaching waste printed circuit board and leaching method thereof

Abstract

The invention discloses gluconobacter oxydans for leaching waste printed circuit boards and a leaching method of the gluconobacter oxydans, and belongs to the technical field of microbial resource recovery treatment, lixivium for leaching extraction comprises the gluconobacter oxydans, metabolites of the gluconobacter oxydans and an H2O2 solution, and the H2O2 solution is added to improve the metal leaching percentage and shorten the leaching time. Compared with traditional chemical and biological leaching, efficient leaching of the metal copper in the waste printed circuit board is achieved under the relatively mild condition, safety is higher, and secondary pollution to the environment can be relieved.

Description

Technical Field

[0001] The invention belongs to the technical field of microbial resource recovery and treatment, and particularly relates to a Gluconobacter oxidans used for leaching waste printed circuit boards and a leaching method thereof. Background Art

[0002] With the rapid development of the electronics industry, the amount of electronic waste has increased dramatically. Among them, waste printed circuit boards, as a common type of electronic waste, contain a large amount of precious metals such as gold, silver, and valuable metals such as copper, iron, and aluminum. Therefore, it is very necessary to recycle them. At present, the commonly used methods for metal recovery from waste printed circuit boards at home and abroad mainly include pyrometallurgy and hydrometallurgy.

[0003] Pyrometallurgy refers to the separation and recovery of metal components in waste printed circuit boards through high-temperature treatment. The process usually includes pretreatment (such as crushing and sorting), pyrolysis and smelting. At high temperatures, organic matter is decomposed and metals are melted, which can effectively separate metals from non-metallic materials. Hydrometallurgy is based on the principle of chemical reaction and uses chemical reagents to leach metals from waste printed circuit boards. Bioleaching is a branch of hydrometallurgy that uses the biochemical action of microorganisms to recover valuable metals from waste printed circuit boards. This method mainly involves the reaction of metabolites (such as acidic substances) produced by microorganisms with metal ions to promote the dissolution of metals from solid matrices into liquid phases, and then through subsequent treatment steps such as precipitation and adsorption, metal enrichment and recovery are achieved. The bioleaching process has mild conditions and has little impact on the environment.

[0004] The process of recycling waste printed circuit boards by pyrometallurgy will produce a large amount of harmful gases, such as dioxins, sulfur oxides and nitrogen oxides, which will seriously pollute the air and endanger human health. At the same time, pyrometallurgy requires high-temperature operation, high energy consumption, and will increase carbon emissions. Hydrometallurgy is divided into chemical methods and microbial methods. The chemical methods mainly use chemical reagents such as strong acids and strong alkalis, while the traditional microbial methods mainly use strong acidophilic bacteria, such as Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans. These methods require additional steps to treat the large amount of acidic and alkaline wastewater generated during the leaching process, otherwise it will seriously threaten the safety of the surrounding water and soil environment. Therefore, it is very necessary to find an environmentally friendly and suitable biological method to recover valuable metals from waste printed circuit boards. Summary of the invention

[0005] In view of the problems in the prior art, the purpose of the present invention is to provide a microorganism for bioleaching waste printed circuit boards, wherein the microorganism is Gluconobacter oxidans, and a method for efficiently recovering valuable metals from waste printed circuit boards using Gluconobacter oxidans is provided.

[0006] The invention provides Gluconobacter oxidans for leaching waste printed circuit boards. The Gluconobacter oxidans is used for leaching and extracting valuable metals in waste printed circuit boards. The Gluconobacter oxidans is an aerobic Gram-negative bacterium with a first-level biosafety level, and mainly metabolizes to produce organic acids such as gluconic acid.

[0007] The Gluconobacter oxidans is used to leach waste printed circuit boards. The leaching solution used for leaching and extraction includes Gluconobacter oxidans and its metabolites and H2O2 solution. The metal leaching percentage is increased and the leaching time is shortened by adding the H2O2 solution.

[0008] The Gluconobacter oxidans is used to leach waste printed circuit boards, and a 30 wt.% H2O2 solution is added, with the addition amount being ≤3.5% v / v.

[0009] The present invention provides a leaching method for leaching waste printed circuit boards using Gluconobacter oxidans, comprising the following steps: Step 1: Obtaining leached powder of waste printed circuit boards for bioleaching; Step 2: preparing a culture medium for culturing Gluconobacter oxidans; Step 3: culturing the Gluconobacter oxidans in the culture medium of step 2 to obtain an extract; Step 4: adding the leached powder from step 1 to the leaching solution from step 3 to carry out bioleaching of valuable metals.

[0010] The leaching method of using Gluconobacter oxydans to leach waste printed circuit boards, wherein the composition of the culture medium in step 2 is: Anhydrous glucose 17.38 g / L, ammonium chloride 1.25 g / L, potassium dihydrogen phosphate 3.00 g / L, dipotassium hydrogen phosphate 1.25 g / L, magnesium sulfate heptahydrate 0.13 g / L, yeast extract 2.50 g / L, and peptone 2.50 g / L.

[0011] The leaching method for using the Gluconobacter oxidans to leach waste printed circuit boards comprises culturing the Gluconobacter oxidans described in step 3 in a culture medium to a logarithmic growth phase to obtain a leaching solution of the Gluconobacter oxidans and its metabolites.

[0012] The leaching method for using Gluconobacter oxidans to leach waste printed circuit boards comprises adding 30 wt.% H2O2 solution to the leaching solution in step 3 to cooperate with Gluconobacter oxidans to enhance the leaching effect.

[0013] In the leaching system of the above leaching method, after leaching the waste printed circuit board powder for 2 days, the copper leaching rate reached 98.1%.

[0014] The leaching method for using the Gluconobacter oxidans to leach waste printed circuit boards comprises culturing the Gluconobacter oxidans described in step 3 in a culture medium until a stable period, and extracting a filtrate of the metabolites of the Gluconobacter oxidans as a leaching solution.

[0015] In the leaching system of the above leaching method, after leaching the waste printed circuit board powder for 7 days, the copper leaching rate reached 48.7%.

[0016] The experimental methods adopted in the present invention include blank control experiments, a two-step method (i.e., first culturing the microorganisms to the logarithmic growth phase, and then adding waste printed circuit board powder to extract metals) and a spent culture medium method (i.e., first culturing the microorganisms to the stable phase, filtering the bacteria, and then using the metabolites produced by them to extract metals) to verify the leaching effects of different methods.

[0017] The present invention is dedicated to efficiently leaching valuable metals from waste printed circuit boards under relatively mild conditions, and studies synergistic substances that can enhance the metal leaching effect of Gluconobacter oxidans, thereby developing a set of environmentally friendly bioleaching technology. This method uses Gluconobacter oxidans, a bacterium with a first-level biosafety level that is harmless to both the environment and the human body, which greatly reduces the adverse effects on the environment caused by traditional treatment with inorganic acids or alkalis, while ensuring efficient leaching of metal resources in waste printed circuit boards. As an aerobic microorganism, Gluconobacter oxidans is known for producing organic acids and is widely used in food processing industries such as wine brewing and the pharmaceutical industry. However, there is currently no precedent for its application in the bioleaching treatment of waste printed circuit board powder. The present invention not only opens up research in the field of microbial resource recovery methods, but also provides a new solution for the environmentally friendly treatment of electronic waste.

[0018] The bioleaching method proposed in the present invention includes screening out valuable materials from waste printed circuit boards as research samples and pre-treating them; then, by culturing Gluconobacter oxidans, experiments are carried out using a variety of leaching methods including a two-step method and a waste culture medium method, aiming to improve the leaching rate and leaching percentage of metals.

[0019] Compared with the existing method, the present invention has the following beneficial effects: 1. The present invention creatively applies Gluconobacter oxidans to biological leaching, and at the same time supplements with different amounts of H2O2 solution. Compared with the traditional biological leaching method, no strong acidophilic bacteria are used, and no strong acidic wastewater is generated. The leaching percentage of valuable metals in waste printed circuit boards by the bacteria can be increased without generating a large amount of strong acid that is harmful to the environment.

[0020] 2. The present invention adopts different leaching methods. When the waste printed circuit board powder is 10.0 g / L, only Gluconobacter oxydans is used for leaching, and the highest copper leaching percentage within 7 days is 48.7%; when different addition amounts of 30wt.% H2O2 solution are used for coordinated leaching, the copper leaching percentage in all biological leaching systems can reach more than 80% within 2 days.

[0021] 3. When the added concentration of waste printed circuit board powder was 10.0 g / L, by adding a small amount of 30 wt.% H2O2 solution for synergistic leaching, the copper leaching percentage increased by more than 40% compared with the leaching system without adding H2O2 solution.

[0022] 4. This method does not use inorganic acid during the leaching process, and the pH value is maintained in the range of 3.0-5.0, which is relatively mild. Compared with traditional chemical and biological leaching, it is safer and can reduce secondary pollution to the environment.

[0023] 5. The culture medium components used in the present invention are optimized to better meet the growth requirements of Gluconobacter oxydans, increase the concentration and activity of the bacterial solution, and ensure a more efficient leaching effect.

[0024] 6. The acidic wastewater produced by the bioleaching method of the present invention has little impact on the environment, meets the requirements of green and sustainable development, and helps promote the development of green recycling technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The present invention is a flow chart of a method for leaching waste printed circuit boards using Gluconobacter oxidans. DETAILED DESCRIPTION

[0026] The present invention uses Gluconobacter oxydans to leach waste printed circuit boards, explores different leaching methods, and enhances the leaching effect by adding H2O2 solution. The specific process is shown in the attached figure. Figure 1 shown.

[0027] Example 1 The leaching method of using Gluconobacter oxidans to leach waste printed circuit boards adopts a two-step leaching method, which specifically includes the following steps: Step 1: Obtaining Waste PCB Leaching Powder for Bioleaching The waste printed circuit boards were purchased from the waste market, and the purchased waste printed circuit boards were pretreated as follows: the first step was to dismantle the waste printed circuit boards, and use wire strippers to remove the electronic components (such as resistors, capacitors, inductors, etc.) and plastic parts on the surface of the waste printed circuit boards; the second step was to use pliers to cut the waste printed circuit boards into small square pieces with a length and width of about 1 cm; the third step was to use a universal grinder for preliminary crushing, and the crushed products were passed through a 100-mesh sieve and ball-milled to obtain waste printed circuit board powder. Finally, the obtained waste printed circuit board powder was passed through a 200-mesh sieve to obtain the waste printed circuit board powder for bioleaching; Take 0.01 g of powder, add 4.0 mL of aqua regia (HNO3:HCl = 1:3, v / v), and place it in a crucible on a stainless steel hot plate (220°C) for digestion. After cooling, dilute the volume to 10.0 mL with 1% dilute nitric acid, and use inductively coupled plasma optical emission spectrometry (ICP-OES) to measure the copper concentration in the digestion solution. The copper content in the waste printed circuit board powder was calculated to be 191.9 mg / g.

[0028] Step 2: Prepare the culture medium for growing Gluconobacter oxydans Add 13.9 g of anhydrous glucose, 1.0 g of ammonium chloride, 2.4 g of potassium dihydrogen phosphate, 1.0 g of dipotassium hydrogen phosphate, 0.1 g of magnesium sulfate heptahydrate, 2.0 g of yeast extract, and 2.0 g of peptone to 800 mL of deionized water; then sterilize the prepared culture medium under high pressure at 121 °C for 20 min.

[0029] Step 3: Obtaining the Leachate Add Gluconobacter oxydans to 100 mL of sterile culture medium to make the initial bacterial concentration 1×10 7 CFU / mL, and culture to the logarithmic growth phase to obtain the extract of Gluconobacter oxydans and its metabolites.

[0030] Step 4: Leaching Add 1.0 g of waste printed circuit board powder to a 250 mL conical flask and sterilize it under high pressure (set the temperature to 121 °C and the sterilization time to 20 min). Add 100 mL of leaching solution to the sterilized conical flask, control the solid-liquid ratio to 10.0 g / L, and ensure that the waste printed circuit board powder is completely immersed in the leaching solution mentioned above; The start of the leaching experiment was recorded as 0 h, the leaching temperature was controlled at 30 °C, the stirring speed was 150 rpm, the leaching time was 7 days, and sampling was carried out at 24 h, 48 h, 72 h, 96 h, 120 h, 144 h, and 168 h; After sampling, the pH value and bacterial concentration of the system should be monitored. The pH value fluctuates within the range of 3.0-4.0 and the bacterial concentration is within the range of 5.75×10 7 CFU / mL-2.33×10 8 If the CFU / mL range fluctuates, it is also necessary to filter the filtrate with a 0.22 μm water filter to measure the copper concentration in the filtrate; The filtrate obtained above was diluted with 1% dilute nitric acid, and the copper concentration was measured by ICP-OES and the leaching percentage was calculated. After 7 days, the copper leaching percentage was 25.1%.

[0031] Example 2 The leaching method of using Gluconobacter oxydans to leach waste printed circuit boards adopts a two-step leaching method, adding H2O2 solution (30 wt.%), and specifically includes the following steps: Step 1: Obtaining Waste PCB Leaching Powder for Bioleaching Same as Example 1.

[0032] Step 2: Prepare the culture medium for growing Gluconobacter oxydans Same as Example 1.

[0033] Step 3: Obtaining the Leachate Add Gluconobacter oxydans to 100 mL of sterile culture medium to make the initial bacterial concentration 1×10 7 CFU / mL, cultured to the logarithmic growth phase, obtained Gluconobacter oxydans and its metabolites, added H2O2 solution to obtain the extract; the experiment was divided into three groups, adding 1.0% (v / v), 2.0% (v / v) and 3.5% (v / v) H2O2 solution respectively.

[0034] Step 4: Leaching The experimental operation of each group was the same. 1.0 g of waste printed circuit board powder was added to a 250 mL conical flask and sterilized by high pressure (the setting temperature was 121 °C and the sterilization time was 20 min). 100 mL of leaching solution was added to the sterilized conical flask, and the solid-liquid ratio was controlled to be 10.0 g / L, and it was ensured that the waste printed circuit board powder was completely immersed in the above-mentioned leaching solution. The start of the leaching experiment was recorded as 0 h, the leaching temperature was controlled at 30 °C, the stirring speed was 150 rpm, the leaching time was 2 days, and samples were taken at 2 h, 6 h, 12 h, 24 h, and 48 h; After sampling, the pH value, ORP value and bacterial concentration of the system should be monitored. The pH value fluctuates in the range of 3.0-5.0, the ORP value fluctuates in the range of 200-500, and the bacterial concentration of 1% (v / v) H2O2 solution is 1.06×108 CFU / mL-1.38×10 8 The CFU / mL range fluctuated, and the bacterial concentration of the added 2% (v / v) H2O2 solution was 7.70×10 7 CFU / mL-1.80×10 8 The CFU / mL range fluctuated, and the bacterial concentration of the added 3.5% (v / v) H2O2 solution was 8.75×10 6 CFU / mL-8.35×10 7 If the CFU / mL range fluctuates, it is also necessary to filter the filtrate with a 0.22 μm water filter to measure the copper concentration in the filtrate; The filtrate obtained above was diluted with 1% dilute nitric acid, the copper concentration was measured by ICP-OES and the leaching percentage was calculated. 1% (v / v), 2% (v / v) and 3.5% (v / v) H2O2 solutions were added. After 2 days, the copper leaching percentages were 84.4%, 98.1% and 98.0%, respectively.

[0035] Example 3 The leaching method of using Gluconobacter oxydans to leach waste printed circuit boards adopts a waste culture medium method, and specifically comprises the following steps: Step 1: Obtaining Waste PCB Leaching Powder for Bioleaching Same as Example 1.

[0036] Step 2: Prepare the culture medium for growing Gluconobacter oxydans Same as Example 1.

[0037] Step 3: Obtaining the Leachate Add Gluconobacter oxydans to 100 mL of sterile culture medium to make the initial bacterial concentration 1×10 7 CFU / mL, after culturing to the stable period, the obtained stable period bacterial liquid was divided into 50 mL centrifuge tubes, placed in a centrifuge, and centrifuged at 4500 r / min for 10 min; then, the centrifuged liquid was filtered through a 0.22 μm water system membrane to obtain the filtrate, i.e., the extract.

[0038] Step 4: Leaching Add 1.0 g of waste printed circuit board powder to a 250 mL conical flask and sterilize it under high pressure (set the temperature to 121 °C and the sterilization time to 20 min). Add 100 mL of leaching solution to the sterilized conical flask, control the solid-liquid ratio to 10.0 g / L, and ensure that the waste printed circuit board powder is completely immersed in the leaching solution mentioned above; The start of the leaching experiment was recorded as 0 h, the leaching temperature was controlled at 30 °C, the stirring speed was 150 rpm, the leaching time was 7 days, and sampling was carried out at 24 h, 48 h, 72 h, 96 h, 120 h, 144 h, and 168 h; After sampling, the pH value of the system should be monitored. The pH value fluctuates between 3.0 and 4.0. It is also necessary to filter the filtrate with a 0.22 μm water filter to measure the copper concentration in the filtrate. The filtrate obtained above was diluted with 1% dilute nitric acid, and the copper concentration was measured by ICP-OES and the leaching percentage was calculated. After 7 days, the copper leaching percentage was 48.7%.

[0039] Example 4 The leaching method of using Gluconobacter oxydans to leach waste printed circuit boards adopts a waste culture medium method and adds H2O2 solution (30 wt.%), which specifically includes the following steps: Step 1: Obtaining Waste PCB Leaching Powder for Bioleaching Same as Example 1.

[0040] Step 2: Prepare the culture medium for growing Gluconobacter oxydans Same as Example 1.

[0041] Step 3: Obtaining the Leachate Add Gluconobacter oxydans to 100 mL of sterile culture medium to make the initial bacterial concentration 1×10 7 CFU / mL, after culturing to the stable period, the obtained stable period bacterial liquid was divided into 50 mL centrifuge tubes, placed in a centrifuge, and centrifuged at 4500 r / min for 10 min; then, the centrifuged liquid was filtered through a 0.22 μm water system membrane to obtain a filtrate, and H2O2 solution was added to obtain an extract; the experiment was divided into three groups, and 1.0% (v / v), 2.0% (v / v) and 3.5% (v / v) H2O2 solutions were added respectively.

[0042] Step 4: Leaching The experimental operation of each group was the same. 1.0 g of waste printed circuit board powder was added to a 250 mL conical flask and sterilized by high pressure (the setting temperature was 121 °C and the sterilization time was 20 min). 100 mL of leaching solution was added to the sterilized conical flask, and the solid-liquid ratio was controlled to be 10.0 g / L, and it was ensured that the waste printed circuit board powder was completely immersed in the above-mentioned leaching solution. The start of the leaching experiment was recorded as 0 h, the leaching temperature was controlled at 30 °C, the stirring speed was 150 rpm, the leaching time was 2 days, and samples were taken at 2 h, 6 h, 12 h, 24 h, and 48 h; After sampling, the changes in the system pH and ORP values ​​should be monitored. The pH value fluctuates in the range of 3.0-5.0, and the ORP value fluctuates in the range of 200-500. It is also necessary to filter the filtrate with a 0.22 μm water filter to measure the copper concentration in the filtrate. The filtrate obtained above was diluted with 1% dilute nitric acid, the copper concentration was measured by ICP-OES and the leaching percentage was calculated. 1% (v / v), 2% (v / v) and 3.5% (v / v) H2O2 solutions were added. After 2 days, the copper leaching percentages were 93.9%, 95.2% and 96.9%, respectively.

[0043] Comparative Example 1 The preparation of the leached powder and the culture medium is the same as in Example 1, except that the leaching steps are as follows: Add 1.0 g of waste printed circuit board powder to a 250 mL conical flask and sterilize it under high pressure (set the temperature to 121 °C and the sterilization time to 20 min). Add 100 mL of sterilization culture medium to the sterilized conical flask and ensure that the waste printed circuit board powder is completely immersed in the above-mentioned leaching solution. The start of the leaching experiment was recorded as 0 h, the leaching temperature was controlled at 30 °C, the stirring speed was 150 rpm, the leaching time was 7 days, and sampling was carried out at 24 h, 48 h, 72 h, 96 h, 120 h, 144 h, and 168 h; After sampling, the pH value of the system should be monitored. The pH value fluctuates between 5.0 and 6.0. It is also necessary to filter the filtrate with a 0.22 μm water filter to measure the copper concentration in the filtrate. The filtrate obtained above was diluted with 1% dilute nitric acid, and the copper concentration was measured by ICP-OES and the leaching percentage was calculated. After 7 days, the copper leaching percentage was 7.1%.

[0044] Comparative Example 2 The preparation of the leached powder and the culture medium is the same as in Example 1, except that the leaching steps are as follows: Add 1.0 g of waste printed circuit board powder to a 250 mL conical flask and sterilize it under high pressure (set temperature to 121 °C, sterilization time to 20 min), add sterilization culture medium and H2O2 solution (30 wt.%) to the sterilized conical flask, totaling 100 mL, of which the H2O2 solution accounts for 1% (v / v), and ensure that the waste printed circuit board powder is completely immersed in the above leachate; repeat the above operation for two groups, only adjusting the proportion of added H2O2 solution to 2.0% (v / v) and 3.5% (v / v), respectively; The start of the leaching experiment was recorded as 0 h, the leaching temperature was controlled at 30 °C, the stirring speed was 150 rpm, the leaching time was 2 days, and samples were taken at 2 h, 6 h, 12 h, 24 h, and 48 h; After sampling, the changes in the pH value and ORP value of the system should be monitored. The pH value fluctuates in the range of 4.0-6.0, and the ORP value fluctuates in the range of 200-500. It is also necessary to filter the filtrate with a 0.22 μm water filter to obtain the filtrate and measure the copper concentration in the filtrate. The filtrate obtained above was diluted with 1% dilute nitric acid, and the copper concentration was measured by ICP-OES and the leaching percentage was calculated. After 2 days, the copper leaching percentages were 28.2%, 44.5% and 58.2%, respectively.

Claims

1. Gluconobacter oxidans is used to leach waste printed circuit boards, characterized in that: Gluconobacter oxidans is used for leaching and extraction of valuable metals from waste printed circuit boards.

2. The Gluconobacter oxidans used for leaching waste printed circuit boards as claimed in claim 1, characterized in that: The leaching solution used for leaching extraction includes Gluconobacter oxidans and its metabolites and H2O2 solution. The metal leaching percentage is increased and the leaching time is shortened by adding H2O2 solution.

3. The method of using Gluconobacter oxidans to leach waste printed circuit boards as claimed in claim 2, characterized in that: Add 30wt.% H2O2 solution, the addition amount is ≤3.5% v / v.

4. The leaching method for leaching waste printed circuit boards using Gluconobacter oxydans according to claim 1, characterized in that: The following steps are involved: Step 1: Obtaining leached powder of waste printed circuit boards for bioleaching; Step 2: preparing a culture medium for culturing Gluconobacter oxydans; Step 3: culturing the Gluconobacter oxidans in the culture medium of step 2 to obtain an extract; Step 4: adding the leached powder from step 1 to the leaching solution from step 3 to carry out bioleaching of valuable metals.

5. The method for leaching waste printed circuit boards using Gluconobacter oxydans as claimed in claim 4, characterized in that: The components of the culture medium in step 2 are: Anhydrous glucose 17.38 g / L, ammonium chloride 1.25 g / L, potassium dihydrogen phosphate 3.00 g / L, dipotassium hydrogen phosphate 1.25 g / L, magnesium sulfate heptahydrate 0.13 g / L, yeast extract 2.50 g / L, and peptone 2.50 g / L.

6. The method for leaching waste printed circuit boards using Gluconobacter oxydans as claimed in claim 4, characterized in that: The Gluconobacter oxidans described in step 3 is cultured in a culture medium until the logarithmic growth phase, to obtain an extract of the Gluconobacter oxidans and its metabolites.

7. The method for leaching waste printed circuit boards using Gluconobacter oxydans as claimed in claim 6, characterized in that: In step 3, 30 wt.% H2O2 solution is added to the leaching solution to cooperate with Gluconobacter oxidans to enhance the leaching effect.

8. The method for leaching waste printed circuit boards using Gluconobacter oxydans as claimed in claim 7, characterized in that: In this leaching system, after leaching the waste printed circuit board powder for 2 days, the copper leaching rate reached 98.1%.

9. The method for leaching waste printed circuit boards using Gluconobacter oxydans as claimed in claim 4, characterized in that: The Gluconobacter oxidans described in step 3 is cultured in a culture medium until a stable period, and a filtrate of the metabolites of the Gluconobacter oxidans is extracted as an extract.

10. The method for leaching waste printed circuit boards using Gluconobacter oxydans as claimed in claim 9, characterized in that: In this leaching system, after leaching the waste printed circuit board powder for 7 days, the copper leaching rate reached 48.7%.

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