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

Abstract

The application discloses a gluconobacter oxydans for leaching waste printed circuit boards and a leaching method thereof, and belongs to the technical field of microbial resource recycling and treatment, wherein a leaching solution for leaching and extraction comprises the gluconobacter oxydans, metabolites of the gluconobacter oxydans and an H2O2 solution, and the percentage of metal leaching and the leaching time are shortened by adding the H2O2 solution. Compared with traditional chemical and biological leaching, the application realizes efficient leaching of copper in the waste printed circuit boards under relatively mild conditions, is more safe, and can reduce secondary pollution to the environment.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of microbial resource recycling and processing, and particularly relates to a Gluconobacter oxydans for leaching waste printed circuit boards and a leaching method thereof. BACKGROUND

[0002] With the rapid development of the electronic industry, the amount of electronic waste has increased dramatically. Waste printed circuit boards, as a common type of electronic waste, contain a large amount of precious metals such as gold and silver, as well as valuable metals such as copper, iron, and aluminum. Therefore, it is necessary to recycle and reuse them. Currently, the commonly used methods for recycling metals from waste printed circuit boards include pyrometallurgy and hydrometallurgy.

[0003] Pyrometallurgy refers to the separation and recovery of metal components in waste printed circuit boards through high-temperature treatment. This process usually includes pretreatment (such as crushing, sorting), pyrolysis, and smelting steps. 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 reactions, using chemical reagents to leach metals from waste printed circuit boards. Bioleaching is a branch of hydrometallurgy, which uses the biochemical action of microorganisms to recover valuable metals from waste printed circuit boards. This method mainly uses the metabolic products (such as acidic substances) produced by microorganisms to react with metal ions, promoting the dissolution of metals from solid substrates into liquid phase, and then through subsequent processing steps such as precipitation, adsorption, etc., to achieve the enrichment and recovery of metals. The bioleaching process has mild conditions and less environmental impact.

[0004] The process of pyrometallurgical recycling of waste printed circuit boards produces a large amount of harmful gases, such as dioxins, sulfur oxides, and nitrogen oxides, which can seriously pollute the air and harm human health. At the same time, pyrometallurgy requires high-temperature operation and has high energy consumption, which increases carbon emissions. Hydrometallurgy is divided into chemical methods and microbial methods, among which the chemical methods mainly use strong acids, strong bases, and other chemical reagents, while the traditional microbial method mainly uses strong acidophilic bacteria such as Acidithiobacillus ferroxidans and Acidithiobacillus thiooxidans. These methods all need 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 necessary to find an environmentally friendly and suitable biological method to recover valuable metals from waste printed circuit boards. SUMMARY

[0005] In view of the problems in the prior art, the present application aims to provide a microorganism bacteria for bioleaching of waste printed circuit boards, which is Gluconobacter oxydans, and a method for efficiently recovering valuable metals from waste printed circuit boards using Gluconobacter oxydans.

[0006] The application provides an oxidizing gluconic acid bacillus for leaching waste printed circuit boards, and the oxidizing gluconic acid bacillus is used for leaching and extracting valuable metals in the waste printed circuit boards.

[0007] The oxidizing gluconic acid bacillus is used for leaching waste printed circuit boards, and a leaching solution for leaching and extraction includes the oxidizing gluconic acid bacillus, metabolites of the oxidizing gluconic acid bacillus and an H2O2 solution, and the percentage of metal leaching and the leaching time are shortened by adding the H2O2 solution.

[0008] The oxidizing gluconic acid bacillus is used for leaching waste printed circuit boards, and 30 wt.% H2O2 solution is added, and the amount of addition is less than or equal to 3.5 % v / v.

[0009] The application provides a leaching method of the oxidizing gluconic acid bacillus for leaching waste printed circuit boards, and the leaching method includes the following steps.

[0010] Step 1: obtaining waste printed circuit board leaching powder for biological leaching;

[0011] Step 2: configuring a culture medium for culturing the oxidizing gluconic acid bacillus;

[0012] Step 3: culturing the oxidizing gluconic acid bacillus in the culture medium in step 2 to obtain a leaching solution;

[0013] Step 4: adding the leaching powder in step 1 into the leaching solution in step 3 to perform biological leaching of valuable metals.

[0014] The leaching method of the oxidizing gluconic acid bacillus for leaching waste printed circuit boards, and components of the culture medium in step 2 are as follows.

[0015] 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.

[0016] The leaching method of the oxidizing gluconic acid bacillus for leaching waste printed circuit boards, and the oxidizing gluconic acid bacillus is cultured in the culture medium to the logarithmic growth phase to obtain a leaching solution of the oxidizing gluconic acid bacillus and metabolites of the oxidizing gluconic acid bacillus.

[0017] The leaching method of the oxidizing gluconic acid bacillus for leaching waste printed circuit boards, and 30 wt.% H2O2 solution is added to the leaching solution in step 3 to enhance the leaching effect in cooperation with the oxidizing gluconic acid bacillus.

[0018] In the leaching system of the leaching method, the leaching rate of copper reaches 98.1% after the waste printed circuit board is leached by the powder for 2 days.

[0019] The leaching method for leaching waste printed circuit boards by the Gluconobacter oxydans in step 3 is used to culture the Gluconobacter oxydans in the culture medium to the stable phase, and the filtrate of the metabolic product of the Gluconobacter oxydans is extracted as the leaching liquid.

[0020] In the leaching system of the leaching method, the leaching rate of copper reaches 48.7% after the waste printed circuit board is leached by the powder for 7 days.

[0021] The experimental method adopted in the present application includes a blank control experiment, a two-step method (i.e., first culturing the microorganism to the logarithmic growth phase, and then adding the waste printed circuit board powder to extract the metal), and a waste culture medium method (i.e., first culturing the microorganism to the stable phase, filtering the bacteria, and then using the metabolic product generated by the bacteria to extract the metal), which verifies the leaching effect of different methods.

[0022] The present application is dedicated to efficiently leaching valuable metals from waste printed circuit boards under relatively mild conditions, and to researching synergistic substances that can improve the metal leaching effect of Gluconobacter oxydans, thereby developing an environmentally friendly biological leaching technology. This method uses Gluconobacter oxydans, a bacterium with a first-class biological safety level, which is harmless to the environment and human body, greatly reducing the adverse effects on the environment caused by traditional inorganic acid or alkali treatment, while ensuring efficient leaching of metal resources in waste printed circuit boards. As an aerobic microorganism, Gluconobacter oxydans is known for producing organic acids and has a wide range of applications in food processing industries such as wine brewing and pharmaceutical industries. However, there is currently no precedent for its application in biological leaching treatment of waste printed circuit board powder. The present application not only opens up research in the field of microbial resource recovery methods, but also provides a new solution for the environmental treatment of electronic waste.

[0023] The biological leaching method proposed in the present application includes screening valuable materials from waste printed circuit boards as research samples and pretreating them; then, by culturing Gluconobacter oxydans, various leaching methods including two-step method and waste culture medium method are used for experiments, aiming to improve the leaching rate and percentage of metals.

[0024] Compared with the existing method, the present application has the following beneficial effects:

[0025] 1. The present invention creatively applies Gluconobacter oxydans to bioleaching, supplemented by adding different amounts of H2O2 solution. Compared with traditional bioleaching methods, this method does not use strong acidophilic bacteria and does not produce strongly acidic wastewater. It can increase the leaching percentage of valuable metals in waste printed circuit boards by the bacteria without producing a large amount of strong acid that is harmful to the environment.

[0026] 2. The present invention adopts different leaching methods. When the waste printed circuit board powder concentration is 10.0 g / L, only Gluconobacter oxydans is used for leaching, and the maximum copper leaching percentage within 7 days is 48.7%. When different addition amounts of 30 wt.% H2O2 solution are used for coordinated leaching, the copper leaching percentage in all biological leaching systems can reach more than 80% within 2 days.

[0027] 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.

[0028] 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.

[0029] 5. The culture medium components used in the present invention have been 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.

[0030] 6. The acidic wastewater generated 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

[0031] Figure 1 The present invention is a flow chart of a method for leaching waste printed circuit boards using Gluconobacter oxidans. DETAILED DESCRIPTION

[0032] 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.

[0033] Example 1

[0034] The leaching method of using Gluconobacter oxydans to leach waste printed circuit boards adopts a two-step leaching method, which specifically includes the following steps:

[0035] Step 1: Obtain waste printed circuit board leaching powder for bioleaching

[0036] The waste printed circuit board was purchased from a waste market. The purchased waste printed circuit board was pretreated as follows: first, the waste printed circuit board was disassembled, and wire strippers were used to remove the surface electronic components (such as resistors, capacitors, inductors, etc.) and plastic parts of the waste printed circuit board; second, the waste printed circuit board was cut into square pieces with a length and width of about 1 cm using a vise; third, a universal crusher was used for preliminary crushing, and the obtained crushed product was ball milled after being passed through a 100-mesh sieve. Finally, the obtained waste printed circuit board powder was passed through a 200-mesh sieve to obtain waste printed circuit board powder for bioleaching;

[0037] Take 0.01 g of the 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 to 10.0 mL with 1% dilute nitric acid. Measure the concentration of copper in the digestion solution using an inductively coupled plasma optical emission spectrometer (ICP-OES). Calculate the copper content in the waste printed circuit board powder to be 191.9 mg / g.

[0038] Step 2: Prepare the culture medium for cultivating Gluconobacter oxydans

[0039] 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 proteose peptone to 800 mL of deionized water. Then sterilize the prepared culture medium at 121°C for 20 min.

[0040] Step 3: Obtain leaching solution

[0041] Add Gluconobacter oxydans to 100 mL of sterilized culture medium to obtain an initial bacterial concentration of 1×10 7 CFU / mL. Cultivate until the logarithmic growth phase to obtain a leaching solution of Gluconobacter oxydans and its metabolites.

[0042] Step 4: Leaching

[0043] Add 1.0 g of waste printed circuit board powder to a 250 mL conical flask and sterilize it at 121°C for 20 min. Add 100 mL of the leaching solution to the sterilized conical flask, control the solid-liquid ratio to be 10.0 g / L, and ensure that the waste printed circuit board powder is completely immersed in the above-mentioned leaching solution;

[0044] The leaching experiment was started at 0 hour, the leaching temperature was controlled at 30 °C, the stirring speed was 150 rpm, the leaching time was 7 days, and the sampling was performed at 24 hours, 48 hours, 72 hours, 96 hours, 120 hours, 144 hours and 168 hours;

[0045] After sampling, the pH value and the change of the bacterial concentration of the system were monitored. The pH value fluctuated in the range of 3.0-4.0, and the bacterial concentration fluctuated in the range of 5.75x10 7 CFU / mL-2.33x10 8 CFU / mL, and the filtrate was obtained by filtering with a 0.22 μm water filter head, and the concentration of copper in the filtrate was measured;

[0046] The filtrate obtained above was diluted with 1 % dilute nitric acid, the concentration of copper was measured by ICP-OES, and the leaching percentage was calculated. The leaching percentage of copper was 25.1 % after 7 days.

[0047] Example 2

[0048] The leaching method of Gluconobacter oxydans for leaching waste printed circuit boards adopts a two-step leaching method, and H2O2 solution (30 wt.%) is added, which specifically includes the following steps:

[0049] Step 1: Obtain waste printed circuit board leaching powder for bioleaching

[0050] The same as Example 1.

[0051] Step 2: Configure culture medium for culturing Gluconobacter oxydans

[0052] The same as Example 1.

[0053] Step 3: Obtain leaching solution

[0054] Gluconobacter oxydans was added to 100 mL sterilized culture medium to obtain an initial bacterial concentration of 1x10 7 CFU / mL, and was cultured to the logarithmic growth phase to obtain Gluconobacter oxydans and its metabolites, and H2O2 solution was added to obtain a leaching solution; three groups of experiments were performed, and 1.0 % (v / v), 2.0 % (v / v) and 3.5 % (v / v) of H2O2 solution were added, respectively.

[0055] Step 4: Leaching

[0056] Each set of experiments was operated identically, 1.0 g of waste printed circuit board powder was added to a 250 mL conical flask, autoclaved (temperature set at 121 °C for 20 min), 100 mL of leaching solution was added to the autoclaved conical flask, the solid-liquid ratio was controlled at 10.0 g / L, and it was ensured that the waste printed circuit board powder was completely immersed in the above-mentioned leaching solution;

[0057] When the leaching experiment started, it 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 sampling was performed at 2 h, 6 h, 12 h, 24 h and 48 h;

[0058] After sampling, the changes in pH value, ORP value and bacterial concentration of the system were monitored, the pH value fluctuated in the range of 3.0-5.0, the ORP value fluctuated in the range of 200-500, the bacterial concentration fluctuated in the range of 1.06x10 8 CFU / mL-1.38x10 8 CFU / mL, the bacterial concentration fluctuated in the range of 7.70x10 7 CFU / mL-1.80x10 8 CFU / mL, the bacterial concentration fluctuated in the range of 8.75x10 6 CFU / mL-8.35x10 7 CFU / mL, and the filtrate was obtained by filtering with a 0.22 pm water filter, and the concentration of copper in the filtrate was measured;

[0059] The filtrate obtained above was diluted with 1 % dilute nitric acid, the concentration of copper was measured using ICP-OES and the leaching percentage was calculated, the leaching percentage of copper after 2 days was 84.4 %, 98.1 % and 98.0 % respectively by adding 1 % (v / v), 2 % (v / v) and 3.5 % (v / v) H2O2 solution.

[0060] Example 3

[0061] The leaching method for leaching waste printed circuit boards by using Gluconobacter oxydans, using waste medium leaching, specifically comprising the following steps:

[0062] Step 1: Obtain waste printed circuit board leaching powder for biological leaching

[0063] The same as Example 1.

[0064] Step 2: Configure the culture medium for culturing Gluconobacter oxydans

[0065] Example 1.

[0066] Step 3: Obtaining the leachate

[0067] Gluconobacter oxydans was added to 100 mL of sterilized medium to achieve an initial bacterial concentration of 1 x 10 7 CFU / mL, and after culturing to the stationary phase, the resulting stationary phase bacterial solution was aliquoted into 50 mL centrifuge tubes and placed in a centrifuge at a speed of 4500 r / min for 10 min. Subsequently, the centrifuged liquid was filtered through a 0.22 μm water-based membrane to obtain the filtrate, i.e., the leachate.

[0068] Step 4: Leaching

[0069] In a 250 mL conical flask, 1.0 g of waste printed circuit board powder was autoclaved (set to a temperature of 121 °C and an autoclaving time of 20 min), and 100 mL of leachate was added to the autoclaved conical flask, with the solid-liquid ratio controlled at 10.0 g / L and ensuring that the waste printed circuit board powder was completely immersed in the above-mentioned leachate;

[0070] When the leaching experiment began, it was recorded as 0 hours, the leaching temperature was controlled at 30 °C, the stirring speed was 150 rpm, and the leaching time was 7 days, with sampling performed at 24 hours, 48 hours, 72 hours, 96 hours, 120 hours, 144 hours, and 168 hours;

[0071] After sampling, the change in the pH value of the system was monitored, with the pH value fluctuating within the range of 3.0-4.0, and the filtrate was obtained by filtering through a 0.22 μm water-based filter head, and the concentration of copper in the filtrate was measured;

[0072] The filtrate obtained above was diluted using 1 % dilute nitric acid, the concentration of copper was measured using ICP-OES, and the leaching percentage was calculated, with the leaching percentage of copper being 48.7 % after 7 days.

[0073] Example 4

[0074] The leaching method for leaching waste printed circuit boards using Gluconobacter oxydans used waste medium leaching, with the addition of H2O2 solution (30 wt.%), and included the following steps:

[0075] Step 1: Obtaining waste printed circuit board leaching powder for bioleaching

[0076] Example 1.

[0077] Step 2: Preparing the culture medium for culturing Gluconobacter oxydans

[0078] Example 1.

[0079] Step 3: Obtaining the Leachate

[0080] 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. Subsequently, the centrifuged liquid was filtered through a 0.22 μm aqueous 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.

[0081] Step 4: Leaching

[0082] Each experimental group followed the same procedure. 1.0 g of waste printed circuit board powder was added to a 250 mL Erlenmeyer flask and sterilized under high pressure (set temperature at 121°C for 20 min). 100 mL of the extract was then added to the sterilized Erlenmeyer flask, maintaining a solid-liquid ratio of 10.0 g / L and ensuring that the waste printed circuit board powder was completely immersed in the extract.

[0083] The start of the leaching experiment was marked as hour 0, 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 hours, 6 hours, 12 hours, 24 hours, and 48 hours;

[0084] After sampling, the changes in the system pH and ORP values ​​should be monitored. The pH value fluctuates within the range of 3.0-5.0, and the ORP value fluctuates within 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.

[0085] 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.

[0086] Comparative Example 1

[0087] The preparation of the leached powder and culture medium is the same as in Example 1, except for the following differences in the leaching steps:

[0088] In a 250 mL conical flask, 1.0 g of waste printed circuit board powder was added, and autoclaved (temperature set at 121 °C, sterilization time for 20 min), 100 mL of sterilized medium was added to the sterilized conical flask, and the waste printed circuit board powder was completely immersed in the above leaching solution;

[0089] The leaching experiment was started at 0 hour, the leaching temperature was controlled at 30 °C, the stirring speed was 150 rpm, the leaching time was 7 days, and the sampling was carried out at 24 hours, 48 hours, 72 hours, 96 hours, 120 hours, 144 hours and 168 hours;

[0090] After sampling, the change of pH value of the system was monitored, the pH value fluctuated in the range of 5.0-6.0, and the filtrate was obtained by filtering with a 0.22 μm water filter, and the concentration of copper in the filtrate was measured;

[0091] The filtrate obtained above was diluted with 1 % dilute nitric acid, the concentration of copper was measured by ICP-OES, and the leaching percentage was calculated, and the leaching percentage of copper was 7.1 % after 7 days.

[0092] Comparative Example 2

[0093] The leaching powder and medium preparation were the same as in Example 1, and the difference in the leaching step was as follows:

[0094] In a 250 mL conical flask, 1.0 g of waste printed circuit board powder was added, and autoclaved (temperature set at 121 °C, sterilization time for 20 min), 100 mL of sterilized medium and H2O2 solution (30 wt.%) were added to the sterilized conical flask, and the waste printed circuit board powder was completely immersed in the above leaching solution; two groups of the above operation were repeated, and only the proportion of H2O2 solution was adjusted, which was 2.0 % (v / v) and 3.5 % (v / v) respectively;

[0095] The leaching experiment was started at 0 hour, the leaching temperature was controlled at 30 °C, the stirring speed was 150 rpm, the leaching time was 2 days, and the sampling was carried out at 2 hours, 6 hours, 12 hours, 24 hours and 48 hours;

[0096] After sampling, the change of pH value and ORP value of the system was monitored, the pH value fluctuated in the range of 4.0-6.0, and the ORP value fluctuated in the range of 200-500, and the filtrate was obtained by filtering with a 0.22 μm water filter, and the concentration of copper in the filtrate was measured;

[0097] The filtrates thus obtained were diluted with 1 % dilute nitric acid and the concentration of copper was measured using ICP-OES and the percentage leaching was calculated, which was 28.2 %, 44.5 % and 58.2 % respectively for copper after 2 days.

Claims

1. A leaching method for leaching waste printed circuit boards using Gluconobacter oxydans, characterized by, The method comprises the following steps: Step 1: obtaining waste printed circuit board leaching powder for bioleaching; Step 2: configuring a culture medium for culturing Gluconobacter oxydans; Step 3: culturing Gluconobacter oxydans in the culture medium of step 2 to the logarithmic growth phase, obtaining a Gluconobacter oxydans and metabolic product leaching solution, adding a 30 wt.% H2O2 solution in an amount of 2.0% to 3.5% v / v to enhance the leaching effect in cooperation with Gluconobacter oxydans; Step 4: adding the leaching powder of step 1 into the leaching solution of step 3 for valuable metal bioleaching.

2. The leaching method for leaching waste printed circuit boards using the Gluconobacter oxydans according to claim 1, wherein The culture medium in step 2 comprises: 17.38 g / L of anhydrous glucose, 1.25 g / L of ammonium chloride, 3.00 g / L of potassium dihydrogen phosphate, 1.25 g / L of dipotassium hydrogen phosphate, 0.13 g / L of magnesium sulfate heptahydrate, 2.50 g / L of yeast extract, and 2.50 g / L of peptone.

3. The leaching method for leaching waste printed circuit boards using the Gluconobacter oxydans according to claim 1, wherein, In the leaching system, after the waste printed circuit board leaching powder is leached for 2 days, the leaching rate of copper reaches 98.1%.

4. The leaching method for leaching waste printed circuit boards using the Gluconobacter oxydans according to claim 1, wherein, The Gluconobacter oxydans in step 3 is cultured in the culture medium to the stationary phase, and the filtrate of the metabolic products of Gluconobacter oxydans is extracted as a leaching solution.

5. The leaching method for leaching waste printed circuit boards using the Gluconobacter oxydans according to claim 4, characterized by, In the leaching system, after the waste printed circuit board leaching powder is leached for 7 days, the leaching rate of copper reaches 48.7%.

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