Nano-enabled Recovery of Scarce Metals: From benchtop to startup
In these days of social distancing, everyday electronic devices such as cell phones and laptops are more crucial than ever. But many of these devices, ubiquitous as they are, contain materials that are difficult to come by, called scarce rare earth and specialty elements (RESEs). For example, audio equipment such as speakers, headphones and microphones, frequently contain neodymium magnets. 1 Every iPhone contains eight different rare-earth metals and some smart phones have as many as seventeen rare-earth metals. 2
image by Terence Wright
However, there is a problem, and it’s serious: for many RESE’s, current demand is outstripping the available supply rates. 3 The situation could soon become even worse, because many wind and solar energy technologies also rely on RESEs. 3 To make the problem even more dire, less than 5% of RESEs are currently recycled. 4 Most likely, your last cell phone is buried in a landfill! This is clearly not sustainable and a significant effort is being directed towards ways to improve both the technology and the community infrastructure to improve this situation.
The insides of your smartphone include multiple rare materials One of the most popular methods of recycling metals is electrowinning . 5-7 This process begins by digesting used products such as electronics with a strong acid, creating a mixture of metal ions in what is commonly referred to as an electronic waste (e-waste) stream. Metals are then recovered from the e-waste by causing the dissolved metal ions to deposit as solid metal atoms onto a negatively charged stainless steel or aluminum sheet.
Zinc electrowinning plant. (Image from Yang et al. 2017, 8 courtesy of Open Access)
This technique works quite well for many bulk metals such as nickel and zinc, 9,10 but the requirement for large and smooth sheets of aluminum or stainless steel mean that a typical electrowinning operation requires a significant amount of space (think of a huge warehouse) to be economically viable. Unfortunately, this conventional approach, called electrodeposition, is impractical for the recovery of many RESEs because of their comparatively low concentrations in most e-waste streams (much less than 1%). 3
Enter nanotechnology! A company called Nth Cycle ( www.nthcycle.com ) was started in 2017 to address the recovery of RESEs from e-waste. The founders were three environmental engineers: Desiree Plata (an Assistant Professor in the Chemical and Environmental Engineering Department at Yale), Megan O’Connor (Dr. Plata’s graduate student at the time), and Chad Vecitis (an Assistant Professor at Harvard at the time). They recognized that carbon nanotubes have unique properties, most notably their high surface area, conductivity and chemical stability that could help extract metals from e-waste using electrodeposition. In contrast to traditional electrowinning, the...