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Biomedical devices

Biomedical devices

Magnetic fields can turn medical waste into high-value products

05 Jul 2022
A new method for medical waste disposal
Waste disposal: A process based on alternating magnetic fields could help process the mountains of medical waste produced during the coronavirus pandemic. (Courtesy: iStock/Snezhana Kudryavtseva)

Alternating magnetic fields can be used to rapidly convert medical waste, such as plastic syringes, into hydrogen-rich gases and high-quality graphite, scientists in China have found. This catalytic technique is more environmentally friendly and less energy intensive than other waste management strategies, the researchers claim. It might also help us dispose of other types of medical waste such as masks and protective clothing.

The coronavirus pandemic produced mountains of medical waste. According to the World Health Organization (WHO), between March 2020 and November 2021, the UN shipped 87,000 tonnes of personal protective equipment (PPE), like masks and gowns, to countries around the world. But this is only the tip of the iceberg, as it does not cover items purchased outside the UN initiative by governments and members of the public. More than 140 million test kits have also been shipped and the more than eight billion vaccine doses administered globally have produced 144 000 tonnes of waste products, such as syringes, needles and sharps bins.

In the rush to secure PPE and administer vaccines, less attention was paid to waste disposal. But that plastic and biohazardous medical waste is threatening human and environmental health, according to a recent WHO report. Now researchers in China claim to have developed a new catalytic technique that rapidly decomposes disposable syringe plastic, which they say could help.

Incineration is widely used to dispose of plastic waste. While it is quick and simple, it can produce large quantities of carbon dioxide and other toxic gases, and the only useful by-product is heat. Plastic in medical waste is rich in hydrogen and recently researchers have developed a two-stage technique that uses high-temperature pyrolysis followed by catalytic cracking to turn it into hydrogen-rich gases such as hydrogen, ethanol and methane. But, according to Xifeng Zhu from the University of Science and Technology of China and his colleagues, this process is very energy intensive.

To address the challenge of efficiently converting medical waste into hydrogen-rich gases, Zhu turned to magnetic hyperthermia. Magnetic hyperthermia generates localized intense heat by subjecting magnetic nanoparticles to a high-frequency alternating magnetic field. So far, this technique has been primarily used within medicine to heat and destroy cancer cells.

The researchers created a catalyst that would respond to a magnetic field by joining ten bent disposable syringe needles together in a chain-like loop. They then added crushed disposable syringes, which were mainly made from polypropylene, and a heavy fraction of bio-oil as an initiator.

When the team subjected this mix to a high-frequency alternating magnetic field they found that the chain-shaped needles heated up. This heated the bio-oil, which then heated the rest of the system. As the temperature increased, the bio-oil and the plastic syringes decomposed, generating hydrogen, methane and other gases. Iron carbide also formed, along with high radio-frequency-electromagnetic-wave-absorbing carbon, which was deposited on the surface of the chain-shaped needle. This graphite caused the whole system to heat even further, reaching temperatures as high as 1200 °C.

As more and more crushed plastic syringes were added to the reaction, without further bio-oil, the formation of graphite and the yield of hydrogen increased. The researchers claim the process was able to turn more than 75% of the hydrogen in the syringes into hydrogen gas and around 68% of their carbon into graphite.

After ten cycles of adding additional syringes, electron microscopy confirmed the growth of a large amount of flaky carbon. It showed that there were seven layers of graphite sheets deposited on the chain-shaped needles, with a lattice structure that contained few defects.

According to the researchers, this technique simplifies the treatment of medical waste by converting it into hydrogen and high-value graphite in a one step process. The use of a high-frequency alternating magnetic field also minimizes the amount of energy used compared with other catalytic process, as the whole reactor does not need to be heated simultaneously.

The research is described in Cell Reports Physical Science.

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