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A Japanese-Italian research team claims to have developed a simple and convenient method for recovering copper wires from PVC cables that involves the use of microwave radiation and avoids the generation or use of toxic chemicals.
Scientists from Sophia University (Japan) and the University of Pavia (Italy) have developed a microwave-induced pyrolysis method to recycle VVF electrical cables (initials for a type of vinyl-insulated flat cable).
The research paper, “ Recycling of e-waste power cables using microwave-induced pyrolysis – process characteristics and facile recovery of copper metal”, published in the journal RSC Advances , states that power cables, composed of copper or aluminium wires, constitute a major waste problem despite being highly recyclable. It adds that the recycling rate of PVC insulation material is currently only 35%, with most of it ending up in landfills.
“VVF cables are commonly used as electrical cables in homes and buildings and have a high reuse value among e-waste,” said Satoshi Horikoshi, one of the lead authors of the study. “Our method is suitable for recycling and recovering metal-containing e-waste and does not require any pretreatment to separate plastics from metals.”
The method developed by the researchers consists of placing VVF electrical cables in a glass reactor where they are subjected to microwave radiation. Pyrolysis carbonises the PVC insulation, leaving the copper wire exposed and allowing it to be easily recovered.
In the study, the researchers tested a standard 54 cm VVF cable and cut pieces of cable of different lengths, 1 cm, 6 cm, 9 cm, 12 cm and 18 cm. They then exposed them to microwave radiation of 100, 200 and 300 W.
The team found that the efficiency of pyrolysis varied with the length of the wire relative to the microwave wavelength, which was about 12.24 cm at a frequency of 2.45 GHz.
Pyrolysis was most effective for wires whose lengths matched specific fractions of the wavelength. Wires measuring 9 cm, equivalent to about 3/4 of the wavelength, and 18 cm, longer than the wavelength, began pyrolyzing after 60 seconds at 100 W. The 3 cm wire, equivalent to about 1/4 of the wavelength, began pyrolysis at 200 W.
Other lengths of 1 cm, 6 cm and 12 cm, which represented integer or nearly integer wavelengths, showed no pyrolysis at 300 W.
With microwaves demonstrating the ability to heat and break wires longer than the wavelength, the 54CM VVF cable was completely pyrolyzed in 12 minutes under 300W radiation, leaving the copper wire intact and undamaged.
This was achieved without generating or using toxic chemicals. The researchers explain that during pyrolysis, the PVC insulation underwent rapid dichlorination and carbonisation, which prevented the formation of harmful by-products such as tar, polycyclic aromatic hydrocarbons and dioxins.
"Clearly, microwave-induced pyrolysis has been shown to be suitable for recycling/recovery of metal-containing e-waste and does not require any pretreatment to separate plastics from metals," the researchers say. |
