United States. Penn State researchers develop a new mussel-inspired nanocellulose coating (MINC) to recover rare earth elements (REEs) from secondary sources, such as industrial wastewater, without using a large amount of energy.
The researchers found inspiration under the sea: the stickiness of the mussel, mimicking natural glue.
REEs play a key role in clean energy, vital for the production of lightweight, efficient batteries and essential components of wind turbines. In contrast, conventional extraction of these elements raises environmental concerns ranging from habitat destruction to water and air pollution and the large amount of energy required to extract and process these elements.
Mussels have a remarkable ability to adhere to underwater surfaces due to the adhesive properties of catechol-based molecules found in mussel proteins. The MINC reflects this by consisting of ultra-small hairy cellulose nanocrystals with exceptionally sticky properties.
MINC is applied to a substrate using a technique called dopamine-mediated advertising layer formation. A chemical reaction allows MINC to form a thin layer of molecules on a surface, making it capable of adhering to a wide range of substrates.
"The MINC approach offers a sustainable and environmentally friendly alternative to conventional extraction methods, minimizing the environmental footprint and contributing to the long-term availability of critical elements," said Amir Sheikhi, assistant professor of chemical engineering and biomedical engineering.
The researchers focused on applying MINC to extract a particular REE, neodymium. The U.S. Department of Energy listed neodymium as a critical material due to supply shortages and its high impact on emerging sustainable technologies such as electric car batteries and magnets used in power systems for electric vehicles and wind turbines.
However, the "rare" part of rare earths is especially true with neodymium, as the lack of a ready-to-extract supply of this critical element forces it to be extracted from secondary sources, such as industrial wastewater recycling. According to Sheikhi, this can be inefficient and energy-intensive.
"The limited global supply of neodymium and the environmental impact of current extraction methods require the development of eco-friendly and sustainable approaches to REE recovery," Sheikhi continued, explaining that conventional extraction techniques use significant amounts of toxic chemicals, such as kerosene, to purify the target element.
"Previous rare earth extraction methods have used adsorbents such as alginate gels, phosphorus sol-gel materials, nanotubes and porous carbon, but these techniques demonstrate limited efficiency," Sheikhi said.
The MINC coating is to neodymium what a magnet is to iron, pulling REE out of water, even when the element is only present in quantities as limited as parts per million.
