A photograph of the plasma discharge at t = 0 seconds. Taken with a color high-speed camera, this image shows the pulse discharge effect on the metal (Al) layer (blue color) as well as its effect on the plastic layer (orange color).
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CREDIT: Prof. Hamid Hosano USAGE RESTRICTIONS: Reprinted from Waste Management, vol. 89, Tomohiko Yamashita, Takashi Sakugawa, Hidenori Akiyama, Hamid Hosano, Metal-coated plastics recycling by pulsed electric discharge, 57-63, 2019, with permission from Elsevier.
22.07.2019/50/20 - As the number of electronic devices increases worldwide, finding effective ways to recycle electronic waste (e-waste) is becoming increasingly important. Every year around 80 million tons of electronic waste are generated, of which only XNUMX% is recycled. Most of the remaining XNUMX% ends up in a landfill where this can become an environmental problem. The current e-waste recycling process uses mechanical crushers and chemical baths, which are expensive, as well as manual labor which, if not done properly, can create significant health and environmental problems. So researchers at Kumamoto University in Japan have used pulsed energy (pulsed electrical discharges) to develop a cleaner, more efficient recycling method.
It has been shown that pulsed energy in the treatment of various waste from concrete to wastewater is successful. To test whether they are suitable for recycling electronic waste, researchers investigated the effectiveness of separating components contained in one of the most prolific types of electronic waste, CD-ROMs. In previous work they have shown that complete separation of metal and plastic with 30 pulses occurs at about 35 J / pulse (at the current electricity price in Tokyo, this amount of energy costs about 0,4 Yen for recycling 100 CD-ROMs). To investigate the mechanism of material separation with this method, researchers performed further analysis by observing plasma discharge with a high-speed camera, using visualizations to assess the shockwave, and using shadowgraph images to measure fragment motion.
Images in the early stage of electrical discharge showed two different light emissions: blue-white and orange. These indicated an excitation of aluminum or upper protective plastics. After the plasma dissolved, metal and plastic fragments flying away from the CD-ROM sample could be seen.
Schlieren images were taken throughout the process, showing that the main destructive shockwaves developed around the two electrodes. The impact created pressure above 3,5 MPa (about the same pressure that a galloping horse puts on the ground) near the electrode tips, and quickly dropped below 0,8 MPa at 7,1 mm. Both in the streaks and in the silhouettes a material distribution was very clearly observed.
"Due to its ubiquity, e-waste may be one of the most important recycling issues we face today," said study leader Professor Hamid Hosano. "Our project has shown how important shockwaves are when pulse energy is used for material removal and separation when recycling electronic waste. We believe that our data will be important for the development of future recycling projects. "
A schlieren image of the shock wave plastic / metal separation induced by the pulsed electric discharge at 4.35 μ. Fragments of the plastic and metal layers (indicated by the white circles) are clearly seen being blown away from the tips of the electrodes where the electric discharge has occurred. [Image details] CREDIT: Prof. Hamid Hosano USAGE RESTRICTIONS: Reprinted from Waste Management, vol. 89, Tomohiko Yamashita, Takashi Sakugawa, Hidenori Akiyama, Hamid Hosano, Metal-coated plastics recycling by pulsed electric discharge, 57-63, 2019, with permission from Elsevier.
Kumamoto University
