Consumer electronics are advancing faster and becoming more affordable by the year, but as exciting as that is for users, it's bad news for the environment. Discarded electronics (or e-waste) brimming with valuable and toxic components is building up in landfills around the world, and it's notoriously tricky to recycle. Now, researchers at Rice University and the Indian Institute of Science have a new way to tackle the e-waste issue: freeze it, grind it into "nanodust" and then sort it out.
In a world where it's tempting to upgrade to a new phone every year or two, e-waste is becoming one of our most pressing environmental concerns. A report released by the United Nations found that, in 2014, less than one sixth of the 42 megatonnes of e-waste produced worldwide was properly recycled or reused, with most ending up in landfills and incinerators. That's wasting huge amounts of valuable and useful metals like iron, gold, silver, copper and aluminum, and leaching toxins like mercury, cadmium and chromium into the environment.
Other projects in progress are trying to tackle the problem by developing biodegradable electronics made out of wood or other plant extracts. For now, though, current methods of recovering those key components often involves chemical treatments.
"In every case, the cycle is one way, and burning or using chemicals takes a lot of energy while still leaving waste," says Chandra Sekhar Tiwary, lead author of the study. "We propose a system that breaks all of the components – metals, oxides and polymers – into homogenous powders and makes them easy to reuse."
Rather than heating things up, which tends to make different elements and materials blend together, the team goes to the other extreme, using liquid nitrogen to cool the waste to a steady 154 K (-119° C, -182° F). At temperatures this low, the materials are much easier to smash up and separate, in a device the team calls a "cryo-mill."
"We take advantage of the physics," says Tiwary. "When you heat things, they are more likely to combine. But in low temperatures, they don't like to mix. The materials' basic properties – their elastic modulus, thermal conductivity and coefficient of thermal expansion – all change. They allow everything to separate really well."
To test their technique, the team threw the printed circuit boards of computer mice into the cryo-mill, which is made up of a container of argon gas and a steel ball. With the liquid nitrogen keeping the components at a constant, ultra-low temperature, the device is shaken so the steel ball grinds the e-waste down over about three hours.
The end result is a powder with particles measuring between 20 and 100 nm each. That nanodust is then bathed in water to separate the polymer, metal and oxide particles from each other, allowing them to be reused with virtually no waste.
The research was published in the journal Materials Today.
Source: Rice University
Update (March 27, 2017): This article originally stated that "less than one sixth of the 42 million megatonnes of e-waste produced worldwide was properly recycled or reused". This was incorrect and should have said "42 megatonnes" – we apologize for the error, which has now been corrected.
