Innovative Microwave Technique for E-Waste Recycling

SEATTLE (Scrap Monster): The demand for electronics has significantly increased. About 62 million tons of e-waste were produced in 2022, an 82 % increase over 2010. According to projections, this number may increase to 82 million tons by 2030.

Reusable rare elements, metals, and semiconductors are among the valuable materials found in e-waste. However, only 22.3% of e-waste was properly collected and recycled in 2022, while the remaining e-waste, valued at approximately $62 billion, was sent to landfills.

Despite ongoing efforts to improve e-waste recycling, the process remains labor-intensive, and much of the e-waste is exported to underdeveloped countries where hazardous chemical recycling methods are supported by cheap labor.

The new process carbonizes the PVC insulation without damaging the copper wire, making recovery easier and preventing the production of highly harmful byproducts.

The researchers placed two-core VVF power cables with copper wires wrapped in PVC insulation inside a glass reactor and exposed them to 100, 200, and 300 W of microwave radiation. During the pyrolysis process, nitrogen gas was introduced into the reactor to prevent combustion. Portions of various cable lengths (1 cm, 6 cm, 9 cm, 12 cm, and 18 cm) were cut and tested alongside a standard 54 cm VVF cable.

Remarkably, the efficiency of the pyrolysis process varied depending on the cable length in relation to the microwave's wavelength, which was approximately 12.24 cm at a frequency of 2.45 GHz. Cables with lengths that corresponded to specific wavelength fractions showed the best results in the pyrolysis process.

After 60 seconds at 100 W, the 9 cm cables (around 3/4 of the wavelength) and the 18 cm cables (longer than the wavelength) began to pyrolyze. In contrast, shorter cables, such as the 3 cm cable (about 1/4 of the wavelength), required more power (200 W) to initiate pyrolysis. Even at 300 W, no pyrolysis occurred with other lengths, such as 1 cm, 6 cm, and 12 cm (full or nearly complete wavelengths).

Although plastics do not absorb microwaves, the 9 cm and 18 cm cables underwent pyrolysis for several reasons. The copper wires acted as antennas at these lengths, absorbing microwave radiation and generating electric arc discharges to heat the PVC without melting the copper. Additionally, the center and ends of these cables experienced a stronger and more concentrated electric field. With an electric field strength roughly double that of the 3 cm wire, the 9 cm wire heated more quickly and locally. Finally, as the PVC heated and carbonized, its ability to absorb microwaves improved, further accelerating the pyrolysis process.

The rapid dichlorination and carbonization of the PVC insulation during the pyrolysis effectively prevented the production of harmful byproducts, such as tar, dioxins, and polycyclic aromatic hydrocarbons (PAHs).

Since the microwaves were able to heat and break down wires longer than their wavelength, the 54 cm VVF cable was fully pyrolyzed in just 12 minutes under 300 W of radiation, leaving the copper wire intact and undamaged.

Currently, only about 35 % of PVC insulation is recycled. This microwave-assisted pyrolysis method provides a more efficient, less labor-intensive way to recover copper wires from PVC cables, improving the recycling process and addressing the growing issue of e-waste.

With this breakthrough, e-waste recycling could become cleaner, faster, and more sustainable, turning today's waste into valuable resources for the future.

Courtesy: www.azom.com