Scientists use microwave radiation to recover copper from old VVF power cables – pv magazine International

November 28, 2024
Patrick Jowett

Scientists from Sophia University in Japan and the Università di Pavia in Italy have developed a microwave-induced pyrolysis method for recycling VVF power cables.

The research work “Recycling electrical waste power cables using microwave-induced pyrolysis – process properties and easy recovery of copper metal“, published in the magazine RSC advances, says Electrical cables, which are made of copper or aluminum wires, represent a significant waste problem despite their high recyclability. She adds that the recycling rate for PVC insulation is currently only about 35%, with the majority ending up in landfills.

“VVF cables are widely used as power cables in homes and buildings and have high reuse value in e-waste,” said Satoshi Horikoshi, one of the study’s lead authors. “Our method is suitable for recycling and reusing metal-containing electronic waste and does not require any pretreatment to separate the plastics from the metals.”

The method developed by the researchers is to lay VVF power cables in one Glass reactor where they are exposed to microwave radiation. Pyrolysis carbonizes the PVC insulation, exposing the copper wire and making it easy to recover.

In the study, researchers tested a standard 54cm VVF cable and cut pieces of different cable lengths of 1cm, 6cm, 9cm, 12cm and 18cm. They were then exposed to microwave radiation of 100, 200 and 300 W.

The team found that the effectiveness of pyrolysis varied with cable length relative to the wavelength of the microwave, which was about 12.24 cm at a frequency of 2.45 GHz.

Pyrolysis was most effective on cables whose length corresponded to certain fractions of the wavelength. The 9 cm cables (equivalent to about 3/4 wavelength) and the 18 cm cables (longer than the wavelength) began to pyrolyze after 60 seconds at 100 W. The 3 cm cable (equivalent to about 1/4 wavelength) started pyrolysis at 200 W.

Other lengths of 1 cm, 6 cm, and 12 cm, representing full or near-full wavelengths, showed no pyrolysis at 300 W.

Since the microwave demonstrated the ability to heat and break wires longer than the wavelength, the 54 cm VVF cable was demonstrated to be completely pyrolyzed under 300 W radiation in 12 minutes, leaving the copper wire intact and remained undamaged.

This was achieved without the production or use of toxic chemicals. The researchers explain that the PVC insulation underwent rapid dichlorination and carbonization during pyrolysis, preventing the formation of harmful byproducts such as tar, polycyclic aromatic hydrocarbons and dioxins.

“Microwave-induced pyrolysis has clearly been shown to be suitable for recycling/recovery of e-waste containing metals and does not require any pretreatment to separate the plastics from the metals,” the researchers said.

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