Method for enhancing biological leaching of copper in waste circuit board by using magnetite

Abstract

The invention discloses a method for enhancing biological leaching of copper in a waste circuit board by utilizing magnetite. The method comprises the following steps: adding the pre-crushed waste circuit board and magnetite into a 9K culture medium with the pH value of 1.8-2.0 according to a certain mass ratio, inoculating Acidithiobacillus ferrooxidans as a leaching strain, and carrying out a leaching reaction under a constant-temperature oscillation condition. The magnetite is added, so that the leaching of copper in the circuit board is remarkably enhanced, the leaching rate is remarkably improved, and the leaching period is shortened. And compared with the microbiological leaching result without magnetite, the copper leaching rate is improved by 12-32%. By utilizing the difference between the circuit board and the magnetite in particle size, the magnetite can be recycled from the leaching residues through a physical separation means for a new round of leaching. The method is simple in process, the strain is easy to culture, and the method has good environmental friendliness and is suitable for green and efficient recovery of copper in the waste circuit board.

Description

Technical Field

[0001] This invention belongs to the field of solid waste resource utilization, and specifically relates to a method for enhancing the bioleaching of copper from waste circuit boards using magnetite. Background Technology

[0002] Printed circuit boards are an important component of electronic and electrical products. As can be seen from the composition of circuit boards, they are made of metal and non-metal components, with metal accounting for about 40% of the total content. Among all metals, copper accounts for about 20%, making it the most abundant metal.

[0003] Currently, methods for extracting metals from waste circuit boards include thermal treatment, mechanical separation, chemical methods, and biological methods. Thermal treatment, such as incineration, produces toxic dioxins; while pyrolysis can reduce harmful gases, it is costly. Mechanical methods are energy-intensive, and the crushing process easily generates dust pollution. Chemical methods consume large amounts of reagents during the reaction process, producing large quantities of waste acid, and are difficult to treat. In contrast, biological methods have gained attention due to their environmental friendliness and low energy consumption. Biological methods refer to the use of oxidation, adsorption, acid dissolution, and other methods to bioleach metals through microorganisms and their metabolites, and are effective in recovering metals from circuit boards. Commonly used microorganisms for leaching include *Thiobacillus ferrooxidans*, *Thiobacillus thiooxidans*, and *Aspergillus niger*. Among them, *Thiobacillus ferrooxidans* can leach Fe... 2+ Oxidized to Fe 3+ It plays a key role in metal leaching and is therefore widely used.

[0004] However, the addition of the circuit board inhibits microbial growth and reduces its oxidation of Fe. 2+ Furthermore, solid particles may cause physical damage to microorganisms, resulting in low leaching efficiency of metals in circuit boards. Summary of the Invention

[0005] In order to overcome the shortcomings of the prior art, the present invention aims to provide a method for enhancing the bioleaching of copper from waste circuit boards using magnetite, so as to improve the leaching rate of metals, represented by copper, from waste circuit boards at a lower cost.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A method for promoting the bioleaching of copper from waste circuit boards using magnetite includes the following steps:

[0008] (1) Cut and crush the waste circuit boards;

[0009] (2) Grind the magnetite;

[0010] (3) Place the prepared culture medium in an Erlenmeyer flask, adjust the pH value of the culture medium to make it a suitable pH value for the growth of inoculated bacteria, and put it in an autoclave for high temperature and high pressure sterilization.

[0011] (4) Add the crushed waste circuit board and magnetite to the sterilized culture medium and inoculate with leaching microorganisms;

[0012] (5) Place the inoculated system in a vertical constant temperature shaker and incubate for 6-8 days;

[0013] (6) Determine the copper leaching rate during the leaching process.

[0014] The above method requires shearing and crushing the waste circuit boards to a particle size range of 0.180mm to 0.425mm, and grinding the magnetite to a particle size of less than 0.037mm.

[0015] In step (4) of the above method, the circuit board and a certain proportion of magnetite are added to a 9K culture medium with the following composition: 3.0 g / L (NH4)2SO4, 0.5 g / L K2HPO4, 0.1 g / L KCl, 0.5 g / L MgSO4, and 0.01 g / L Ca(NO3)2, and 20–44.7 g / L FeSO4·7H2O is added as a nutrient. The pH of the leaching system is adjusted to 1.8–2.0 by adding dilute sulfuric acid and other reagents. Acidithiobacillus ferrooxidans is used as the leaching strain. The temperature of the vertical constant temperature shaker is adjusted to 30–35℃, the rotation speed is 160–180 r / min, and the leaching is carried out for 7 days.

[0016] In step (4) of the above method, the mass ratio of magnetite to circuit board is 0.5:1 to 2:1, and the concentration of circuit board in the entire reaction system is 10 g / L.

[0017] In step (4) of the above method, the initial bacterial concentration in the leaching system after inoculation is 1.0 × 10⁻⁶. 7 ~5.0×10 7 per mL.

[0018] The advantages of this invention lie in its simple leaching method, the addition of magnetite which improves the efficiency of copper leaching from circuit boards, reduces the impact of circuit board particles on bacteria, and the fact that magnetite is almost insoluble and can be recycled after leaching for reuse in a new round of leaching. The overall method can more efficiently leach copper from circuit boards, is simple and environmentally friendly, requires low investment and low energy consumption, and is suitable for the efficient recycling of copper from waste circuit boards. Detailed Implementation

[0019] The embodiments of the present invention will be described in detail below with reference to examples.

[0020] This invention provides a low-cost and high-efficiency process for enhancing copper bioleaching from waste circuit boards using magnetite. Furthermore, the magnetite used in the leaching process can be recycled and reused in a new round of leaching, resulting in significant economic benefits and avoiding environmental pollution from waste circuit boards. The specific steps include:

[0021] Step (1) involves shearing and crushing the waste circuit boards into particles ranging from 0.180 mm to 0.425 mm. In this invention, the Cu content in the waste circuit boards is 24.3% by weight.

[0022] Step (2) involves grinding the magnetite to a particle size of less than 0.037 mm. In this invention, the magnetite contains 69.67% Fe and 25.82% O by weight.

[0023] Step (3): Place the prepared culture medium in an Erlenmeyer flask, adjust the pH value of the culture medium to a suitable pH value for the growth of inoculated bacteria, and put it in an autoclave for high temperature and high pressure sterilization.

[0024] Specifically, the present invention selects 9K culture medium, the composition of which is: (NH4)2SO4 3g / L, K2HPO4 0.5g / L, MgSO4·7H2O 0.5g / L, Ca(NO3)2 0.01g / L, KCl 0.1g / L, and adds 20-44.7g / L FeSO4·7H2O as nutrients, and adds dilute sulfuric acid to adjust the pH of the leaching system to 1.8-2.0.

[0025] Step (4): Add the crushed circuit board and magnetite to the sterilized culture medium. The concentration of the circuit board in the whole reaction system is 10 g / L, and the mass ratio of magnetite to circuit board is 0.5:1 to 2:1. Inoculate with leaching microorganisms.

[0026] This invention uses magnetite as an auxiliary material for enhancement to improve leaching efficiency. Magnetite has good electrical conductivity and can pass through Fe... 2+ / Fe 3+ The transfer of electrons is achieved through valence state transformation. Furthermore, magnetite is recyclable and environmentally friendly. This invention proposes using magnetite to enhance the bioleaching of copper in circuit boards, which not only improves the copper recovery rate but also takes into account sustainability and environmental friendliness.

[0027] In this invention, the leaching microorganism is a mesophilic bacterium—Acidithiobacillus ferrooxidans, and the initial bacterial concentration in the leaching system is 1.0 × 10⁻⁶. 7 ~5.0×10 7 per mL.

[0028] Step (5): Place the inoculated system in a vertical constant temperature shaker for incubation. The temperature of the constant temperature shaker is 30-35℃, the rotation speed is 160-180rpm, and the leaching time is 7 days.

[0029] Clearly, the addition of magnetite significantly enhances copper leaching from circuit boards, substantially increasing the leaching rate and shortening the leaching cycle. Compared to microbial leaching without magnetite, the copper leaching rate is increased by 12%–32%. Utilizing the particle size difference between circuit boards and magnetite, magnetite can be recovered from the leaching residue through physical separation for use in a new round of leaching. This invention features a simple process, easy-to-cultivate microorganisms, and good environmental friendliness, making it suitable for the green and efficient recovery of copper from waste circuit boards.

[0030] The following examples further illustrate the leaching scheme and effects of the present invention. In each example, *Thiobacillus ferrooxidans* is used as the leaching microorganism.

[0031] Example 1:

[0032] Waste circuit boards with a Cu content of 24.3% were crushed to a size of 0.180 mm–0.425 mm and added together with magnetite crushed to a size of less than 0.037 mm in a 9K culture medium containing microorganisms, with 44.7 g / L FeSO4·7H2O added as a nutrient. The leaching conditions were: circuit board slurry concentration of 10 g / L, magnetite to circuit board mass ratio of 0.5:1, initial pH of 2.0, and initial bacterial concentration in the leachate after inoculation of 2.0 × 10⁻⁶. 7 The copper leaching rate was 85.08%, 17.87% higher than that of the control group, using a vertical constant-temperature shaker at 35℃ and 170r / min for 7 days. A control group without magnetite was also included, with all other conditions being the same. After 7 days of leaching, the copper leaching rate in the circuit board reached 85.08%, which was 17.87% higher than that in the control group.

[0033] Example 2:

[0034] Waste circuit boards with a Cu content of 24.3% were crushed to a size of 0.180 mm–0.425 mm and added together with magnetite crushed to a size of less than 0.037 mm in a 9K culture medium containing microorganisms, with 44.7 g / L FeSO4·7H2O added as a nutrient. The leaching conditions were: circuit board slurry concentration of 10 g / L, magnetite to circuit board mass ratio of 1.5:1, initial pH of 2.0, and initial bacterial concentration in the leachate after inoculation of 2.0 × 10⁻⁶. 7 The copper leaching rate was 96.12%, which was achieved by using a vertical constant-temperature shaker at 35℃ and a rotation speed of 170 r / min for 7 days. After 7 days of leaching, the copper leaching rate in the circuit board reached 96.12%, which was 28.91% higher than that of the control group.

[0035] Example 3:

[0036] Waste circuit boards with a Cu content of 24.3% were crushed to a size of 0.180 mm–0.425 mm and added together with magnetite crushed to a size of less than 0.037 mm in a 9K culture medium containing microorganisms, with 44.7 g / L FeSO4·7H2O added as a nutrient. The leaching conditions were: circuit board slurry concentration of 10 g / L, magnetite to circuit board mass ratio of 2:1, initial pH of 2.0, and initial bacterial concentration in the leachate after inoculation of 2.0 × 10⁻⁶. 7 The copper leaching rate was 99.64% (units / mL), achieved using a vertical constant-temperature shaker at 35℃ and a rotation speed of 170 r / min for 7 days. A control group without magnetite was also included, operating under identical conditions except for the absence of magnetite. After 7 days of leaching, the copper leaching rate in the circuit board reached 99.64%, which was 32.43% higher than that of the control group.

[0037] Example 4:

[0038] Waste circuit boards with a Cu content of 24.3% were crushed to a size of 0.180 mm–0.425 mm and added together with magnetite crushed to a size of less than 0.037 mm in a 9K culture medium containing microorganisms, with 30 g / L FeSO4·7H2O added as a nutrient. The leaching conditions were: circuit board slurry concentration of 10 g / L, magnetite to circuit board mass ratio of 2:1, initial pH of 2.0, and initial bacterial concentration in the leachate after inoculation of 2.0 × 10⁻⁶. 7 The copper leaching rate was 87.88%, 12.47% higher than that of the control group. The leaching was performed in a vertical constant-temperature shaker at 35℃ and 170 r / min for 7 days. A control group without magnetite was also included, with all other conditions identical except for the absence of magnetite. After 7 days of leaching, the copper leaching rate in the circuit board reached 87.88%, which was 12.47% higher than that of the control group.

[0039] Example 5:

[0040] Waste circuit boards with a Cu content of 24.3% were crushed to a size of 0.180 mm–0.425 mm and added together with magnetite crushed to a size of less than 0.037 mm in a 9K culture medium containing microorganisms, with 20 g / L FeSO4·7H2O added as a nutrient. The leaching conditions were: circuit board slurry concentration of 10 g / L, magnetite to circuit board mass ratio of 2:1, initial pH of 2.0, and initial bacterial concentration in the leachate after inoculation of 2.0 × 10⁻⁶. 7 The copper leaching rate was 84.79% (units / mL), achieved using a vertical constant-temperature shaker at 35℃ and a rotation speed of 170 r / min for 7 days. A control group without magnetite was also included, operating under identical conditions except for the absence of magnetite. After 7 days of leaching, the copper leaching rate in the circuit board reached 84.79%, which was 12.78% higher than that of the control group.

[0041] Example 6:

[0042] Based on the difference in particle size between circuit boards and magnetite, the magnetite that participated in the leaching process can be separated from the leaching residue and reused for leaching. Waste circuit boards with a Cu content of 24.3% were crushed to 0.180 mm–0.425 mm and fed together with the magnetite screened from the leaching residue into a 9K culture medium containing microorganisms, with 44.7 g / L FeSO4·7H2O added as a nutrient. The leaching conditions were: circuit board slurry concentration of 10 g / L, magnetite to circuit board mass ratio of 2:1, initial pH of 2.0, and initial bacterial concentration in the leachate after inoculation of 2.0 × 10⁻⁶. 7 The copper leaching rate was 97.12%, achieved using a vertical constant-temperature shaker at 35℃ and a rotation speed of 170 r / min for 7 days. After 7 days of leaching, the copper leaching rate in the circuit board reached 97.12%, which was only 2.52% lower than the leaching rate under the same conditions when magnetite was leached for the first time. This indicates that leaching magnetite again can still achieve relatively good results.

Claims

1. A method for enhancing the bioleaching of copper from waste circuit boards using magnetite, characterized in that, Crushed waste circuit boards and magnetite are added to the sterilized culture medium, and leaching microorganisms are inoculated. Copper leaching is completed after 6-8 days.

2. The method for enhancing copper bioleaching from waste circuit boards using magnetite according to claim 1, characterized in that, After being sheared and crushed, the waste circuit boards have a particle size of 0.180mm to 0.425mm; the magnetite is ground into particles with a particle size of less than 0.037mm.

3. The method for enhancing copper bioleaching from waste circuit boards using magnetite according to claim 1 or 2, characterized in that, The mass ratio of magnetite to crushed waste circuit boards is 0.5:1 to 2:1, and the concentration of circuit boards in the entire reaction system is 10 g / L.

4. The method for enhancing copper bioleaching from waste circuit boards using magnetite according to claim 1, characterized in that, The leaching microorganism is Acidithiobacillus ferrooxidans.

5. The method for enhancing copper bioleaching from waste circuit boards using magnetite according to claim 4, characterized in that, The culture medium is 9K medium, which consists of 3.0 g / L (NH4)2SO4, 0.5 g / L K2HPO4, 0.1 g / L KCl, 0.5 g / L MgSO4, 0.01 g / L Ca(NO3)2, and 20–44.7 g / L FeSO4·7H2O as nutrients.

6. The method for enhancing copper bioleaching from waste circuit boards using magnetite according to claim 1, 4, or 5, characterized in that, In the leaching system, the initial bacterial concentration was 1.0 × 10⁻⁶. 7 ~5.0×10 7 Cells / mL, initial pH value 1.8–2.

0.

7. The method for enhancing copper bioleaching from waste circuit boards using magnetite according to claim 1, characterized in that, The inoculated leaching system was placed in a vertical constant temperature shaker for incubation at a temperature of 30–35°C and a rotation speed of 160–180 r / min.

8. The method for enhancing copper bioleaching from waste circuit boards using magnetite according to claim 1, characterized in that, After leaching is completed, the magnetite is recovered and reused in a new round of leaching.