Research Article pubs.acs.org/journal/ascecg
Environment-Friendly Technology of Recovering Full Resources of Waste Capacitors Jujun Ruan,* Jie Zheng, Lipeng Dong, and Rongliang Qiu* School of Environmental Science and Engineering, Sun Yat-Sen University, 135 Xingang Xi Road, Guangzhou 510275, People’s Republic of China
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S Supporting Information *
ABSTRACT: High quantities of waste printed circuit boards (PCBs) have been produced along with the generation of e-waste in the world. High purity metals were contained in waste PCBs. Recovery of waste PCBs caused serious pollution in China. With the view of environment protection, new technologies have been proposed to recover resources from basal boards of waste PCBs. Besides basal boards, waste PCBs contain many electronic components. However, little recovery technology was reported for electronic components. An environmental-friendly technology was proposed to recover waste capacitors of waste PCBs. The materials comprising waste capacitors were liberated by crushing. Then, ferrous metals (nickel alloy) and nonferrous metals (aluminum) were separated from crushed waste capacitors by magnetic/eddy current separation. Nickel alloy particles and aluminum particles can be sent to smelting plants. The optimized operation parameters of magnetic/eddy current separation were fed at speeds of 0.5 m/s, and the rotation speed of the magnetic field was 4.0 m/s. Nonmetallic materials of waste capacitors were translated to oils (boiling points Lmax(metal) + Lmax(nonmetal)
3. RESULTS AND DISCUSSION 3.1. Crushing of Waste Capacitors. When waste capacitors were crushed into the size of 5 mm, all of the comprised materials were completely liberated (see Figure 5). The particle sizes of the crushed materials ranged from 3 to 5 mm. The mass of aluminum particles ranged from 0.007g to 0.02 g. The mass of the nickel alloy particle ranged from 0.006 to 0.01 g. The mass of rubber particles ranged from 0.021 to 0.053 g. The mass of plastic particles ranged from 0.003 to 0.007 g. The mass of paper particles ranged from 0.001 to 0.003 g. 3.2. Magnetic Separation and Eddy Current Separation of Crushed Waste Capacitors. Results of magnetic separation and eddy current separation are presented in Table 1. Magnetic separation and eddy current separation were performed at the same time by the rotation of the magnetic/
(5)
where Lmax(metal) is the maximum size of the nonferrous metallic particle, and Lmax(nonmetal) is the maximum size of nonmetallic particles. 2.3. Vacuum Pyrolysis of Nonmetallic Materials of Waste Capacitors. Vacuum pyrolysis is a green technology for recovering organic materials from crushed e-waste.24,25 Vacuum pyrolysis was employed to treat nonmetallic materials of crushed waste capacitors. The nonmetallic materials included plastics, rubber, and electrode paper. Vacuum pyrolysis was operated under vacuum conditions. 290
DOI: 10.1021/acssuschemeng.6b01569 ACS Sustainable Chem. Eng. 2017, 5, 287−293
Research Article
ACS Sustainable Chemistry & Engineering
particles in eddy current separation should be 0.01m greater than that of nonmetallic particles. The horizontal movements of aluminum particles and nonmetallic particles were measured in different operation parameters of eddy current separation. The results are presented in Table 1. The minim distance between the horizontal movements of aluminum particles and nonmetallic particles was 0.025 m, which was greater than 0.01m. It showed that aluminum particles could be separated from nonmetallic particles completely by eddy current separation with the different operation parameters. It can be seen from Table 1 that the optimized operation parameters for magnetic/ eddy current separation are feeding speed 0.5 m/s and rotation speed of magnetic field 4 m/s. Table 1 also shows that the horizontal movements of plastic and paper particles were smaller than that of rubber. The reason is that plastic and paper particles had rather small mass and large two-dimensional size. In eddy current separation, air friction could not be neglected. Air friction would bring negative impact on the horizontal movements of plastic and paper particles. At last, the recovered nickel alloy particles and aluminum particles can be sent to smelting plants for producing raw materials. 3.3. Vacuum Pyrolysis of Nonmetallic Components. After magnetic/eddy current separation, the nonmetallic particles were sent to a vacuum pyrolysis furnace to obtain oil fuels. In the pyrolysis process of nonmetallic materials of waste capacitors, the vacuum degree of the furnace was decreased into 0.1 Pa. Then, the temperature of the furance began to increase. The temperature increase of the vacuum pyrolysis process is presented in Figure 6a. At the beginning, the heating rate was 5 °C/min until the temperature reached 300 °C from room temperature. The temperature was kept at 300 °C about 10 min in order to make the alundum tube evenly heated and have long-life. Then, the temperature was increased to 800 °C with the heating rate 5 °C/min. When the pyrolysis process was finished, the temperature in section T1 was decreased to 300 °C with the cooling rate 5 °C/min by the temperature controlling system. Afterward, the temperature decreased to room temperature by the method of natural cooling. The variation of air pressure in the vacuum pyrolysis process of nonmetallic materials of a waste capacitor is presented in Figure 6b. When the heating time reached 70 min (heating time 60 min and kept constant temperature 10 min) and the temperature reached 300 °C, the air pressure increased to 0.28 Pa, and a wave peak appeared before the
Figure 5. Crushed materials of waste capacitors.
eddy current separator. Because of the magnetic characteristic, nickel alloys were attached to the magnetic drum and then were detached into Tank A by the striping of the conveyor. The rotation speed of the magnetic field provided little influence on magnetic separation. Magnetic separation results indicate that high feeding speed brought negative impact on the separation rate. The reason was that feeding speed caused a high centrifugal effect to destroy the action of magnetic force. When the feeding speed was 0.5 m/s, the separation rate of magnetic separation reached 100%. It meant that the nickel alloy could be separated from the crushed waste capacitor completely. When the feeding speed increased to 1.0 m/s, the separation rate decreased to 99.7%. When the feeding speed continued to grow up to 2.0 m/s, the separation rate declined to 98.9%. During magnetic separation, eddy current separation was also performed with the rotation of the magnetic field. Aluminum particles subjected to eddy current force and were separated from nonmetallic particles. The largest size of aluminum particles and nonmetallic particles in crushed waste capacitors was 5 mm. Thus, Lmax(metal) + Lmax(nonmetal) was 0.01 m. It meant that if the aluminum particle wanted to be separated from nonmetallic particles, the horizontal movement of aluminum
Table 1. Results of Magnetic Separation and Eddy Current Separation eddy current separation feeding speed (v, m/s)
rotation speed of magnetic field (ω, m/s)
Dm, (m)
Dn(rubber) (m)
Dn(plastic) (m)
Dn(paper) (m)
Dmin (m)
separation rate of magnetic separation
0.5
1.0 2.0 3.0 4.0 1.0 2.0 3.0 4.0 1.0 2.0 3.0 4.0
0.287 0.294 0.302 0.307 0.494 0.501 0.506 0.518 0.882 0.885 0.886 0.889
0.214
0.103
0.095
100%
0.429
0.286
0.197
0.857
0.442
0.275
0.073 0.080 0.088 0.093 0.065 0.072 0.077 0.089 0.025 0.028 0.029 0.032
1.0
2.0
291
99.7%
98.9%
DOI: 10.1021/acssuschemeng.6b01569 ACS Sustainable Chem. Eng. 2017, 5, 287−293
Research Article
ACS Sustainable Chemistry & Engineering
Figure 6. Temperatures and pressures of the vacuum pyrolysis process of nonmetallic materials of waste capacitors.
heating time was 50 min. During this period, paper was the main pyrolysis material, and the plastics began to liquefy. When the heating time lasted to 75 min and the temperature reached about 350 °C, the plastics and rubber began to pyrolyze, and a lot of oil gases were generated. The air pressure reached 1.4 Pa immediately. Under the operation of a vacuum pump, the oil gases were pumped to section T2 and T3, and oil gases were condensed and liquefied to oil. Thus, with the increasing of temperature, nonmetallic materials were pyrolyzed into oil gases and condensed to oil in sections T2 and T3. The air pressure in the furnace fluctuated, and the highest air pressure could reach 1.9 Pa. When the heating time reached 160 min and the temperature was 800 °C, the air pressure decreased dramatically, and fewer and fewer gases were generated during pyrolysis. The oil gases were pumped into sections T2 and section T3 and liquefied to oil, and the air pressure constantly decreased to 0.1 Pa (initial pressure). It meant the pyrolysis process of the nonmetallic materials was finished. Then, we collected liquid oil in the crucible of section T3 (see Figure 4) and some residual carbon in the crucible of section T1 (see Figure 4). There was little oil presented in the crucible of section T2 (see Figure 4). It indicated that there was no oil, whose boiling point was between 100 and 200 °C, generated in the vacuum pyrolysis of nonmetallic materials of a waste capacitor. We employed the method of FT-IR to analyze the functional group contained in the collected oil. The results were placed in Figure 7. The most intense absorption peaks appeared at 2851 cm−1−2920 cm−1. Compared to the spectrogram of the infrared spectra analysis,26 it indicated that abundant alkane existed in the oil. At the wavenumbers of 1732, 1376, and 1460 cm−1, absorption peaks appeared. These were the flexural vibrating frequencies of C−H bonds. Meanwhile, absorption peaks appeared at the wavenumber of 1282 cm−1. It meant that a lot of Si-CH3 groups were present in the pyrolysis oil. The absorption peaks around the wavenumber 698 cm−1 showed that a certain amount of C−Cl groups existed in the pyrolysis oil. In future work, maybe the pyrolysis oil should be further treated in order to obtain pure organic products by the method of supercritical fluid extraction. The utilization of residual carbon needs to be developed. It may be used as adsorbing material to reduce the pollutants in water, soil, and air. Meanwhile, small molecule organic gases generated in the vacuum pyrolysis process should be investigated, although their proportions were rather low.
Figure 7. Analysis of the FT-IR of the pyrolysis oil of nonmetallic materials of waste capacitors.
4. CONCLUSION In this study, an environmental-friendly technology was proposed to recover waste capacitors of waste PCBs. It consisted of crushing, magnetic/eddy current separation, and vacuum pyrolysis. The materials comprising waste capacitors were liberated by crushing, and then, ferrous metals (nickel alloy) and nonferrous metals (aluminum) were separated from crushed waste capacitors by magnetic/eddy current separation. Nickel alloy and aluminum particles could be sent to smelting plants for producing raw materials. Feeding speed would bring negative impact on separation rates of magnetic separation and eddy current separation. The optimized operation parameters of magnetic/eddy current separation were a feeding speed of 0.5 m/s and a rotation speed of the magnetic field of 4.0 m/s. The nonmetallic materials of waste capacitors were treated by the method of vacuum pyrolysis and were translated to oils. The oils had boiling points less than 100 °C. The oils were rich in alkane, Si-CH3 groups, and C−Cl groups. The oils need to be refined for pure organic products in future work.
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ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acssuschemeng.6b01569. 292
DOI: 10.1021/acssuschemeng.6b01569 ACS Sustainable Chem. Eng. 2017, 5, 287−293
Research Article
ACS Sustainable Chemistry & Engineering
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Shearing machine for crushing the waste capacitors and configurations of the employed eddy current separator and vacuum furnace (PDF)
AUTHOR INFORMATION
Corresponding Authors
*(J.R.) Tel: +86 20 84113620. Fax: +86 20 84113620. E-mail:
[email protected]. *(R.Q.) E-mail:
[email protected]. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China (51308488), the Science and Technology Programs of Guangdong province (2015B020237005, 2016A020221014), and the Natural Science Foundation of Jiangsu province (BK20130449). We are grateful to the reviewers who helped us improve the article with their many pertinent comments and suggestions.
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DOI: 10.1021/acssuschemeng.6b01569 ACS Sustainable Chem. Eng. 2017, 5, 287−293
