Researchers at Penn State University developed a new mussel-inspired nanocellulose coating (MINC) that has demonstrated what they call a “remarkable, even surprising” ability to recover rare earth elements from secondary sources, such as industrial wastewater, without using a high amount of energy.
In a paper published in the journal ACS Applied Materials and Interfaces, the scientists explain that mussels have a remarkable ability to adhere to surfaces underwater thanks to the adhesive properties of catechol-based molecules found in mussel proteins. The MINC mirrors this by consisting of ultra-tiny hairy cellulose nanocrystals with uniquely sticky properties.
The novel nanocellulose coating is applied to a substrate via a technique called dopamine-mediated ad-layer formation. A chemical reaction enables it to form a thin layer of molecules on a surface, making it capable of sticking to a broad range of substrates.
“The MINC approach offers a sustainable and eco-friendly alternative to conventional extraction methods, minimizing the environmental footprint and contributing to the long-term availability of critical elements,” Amir Sheikhi, lead author of the paper, said in a media statement.
The researcher and his co-authors focused on applying MINC to extract a particular REE, neodymium.
The “rare” part of rare earth elements is especially true with neodymium, as the lack of ready-to-extract supply of this material forces recovery from secondary sources such as industrial wastewater recycling. According to Sheikhi, this can be both inefficient and energy intensive.
Environmentally friendly approach
“The limited global supply of neodymium and the environmental impact of current extraction methods necessitate the development of eco-friendly and sustainable approaches for REE recovery,” the researcher said, explaining that conventional extraction techniques use significant amounts of toxic chemicals, such as kerosene.
“Prior rare earth extraction methods have utilized adsorbents such as alginate gels, phosphorus sol-gel materials, nanotubes and porous carbon, but these techniques demonstrate limited efficiency,” he pointed out.
The MINC coating is to neodymium what a magnet is to iron, pulling the REE out of water, even when the element is only present in amounts as limited as parts per million.
“The challenge in extracting neodymium lies in achieving efficient and selective removal of it at low concentrations,” Sheikhi said. “The MINC presented in this study offers improved selectivity and capacity for neodymium removal, overcoming limitations of previous methods.”
This selectivity allows MINC to avoid recovering undesired elements like sodium and calcium, which would waste time and energy if they had to be filtered to further refine the neodymium.
“The public and society will benefit from this work through the potential for increased availability of neodymium, a crucial element for not just developing clean energy technologies, but also for creating new medical and electronic devices,” Sheikhi said, noting that he plans to investigate how the MINC method may work to extract other REEs.
