Tomatoes, corncobs and other organic materials have been used to capture rare earth elements from electronic waste, offering a potential alternative to environmentally damaging mining practices.
Researchers from Penn State university in Pennsylvania used micro- and nanoparticles created from the organic materials to capture neodymium from aqueous solutions.
“Waste products like corncobs, wood pulp, cotton and tomato peels often end up in landfills or in compost,” said assistant professor Amir Sheikhi, a corresponding author of a paper on the work. “We wanted to transform these waste products into micro- or nanoscale particles capable of extracting rare earth elements from electronic waste.”
Rare earth metals are used to manufacture strong magnets used in motors for electric and hybrid cars, loudspeakers, headphones, computers, wind turbines, TV screens and more. Mining these metals is challenging and environmentally costly, Sheikhi said, as large land areas are required to mine even small amounts of the metals. Some efforts have turned to recycling the metals from electronic waste like old computers or circuit boards.
The challenge lies in efficiently separating the metals from refuse, Sheikhi said.
“Using the organic materials as a platform, we created highly functional micro- and nanoparticles that can attach to metals like neodymium and separate them from the fluid that surrounds them,” Sheikhi said. “Via electrostatic interactions, the negatively-charged micro- and nano-scale materials bind to positively-charged neodymium ions, separating them.”
To prepare the experiment, Sheikhi’s team ground up tomato peel and corncobs and cut wood pulp and cotton paper into small, thin pieces and soaked them in water. They then chemically reacted the materials in a controlled fashion to disintegrate them into three distinct categories of functional materials – microproducts, nanoparticles and solubilised biopolymers. Adding the microproducts or nanoparticles to neodymium solutions triggered the separation process, resulting in the capture of neodymium samples.
In the most recent paper, Sheikhi improved upon the separation process demonstrated in previous work and extracted larger sample sizes of neodymium from less concentrated solutions.
The researchers plan to extend the separation mechanism into real-world scenarios and partner with interested industries to further test the process.
“In the near future, we want to test our process on realistic industrial samples,” Sheikhi said. “We also hope to tune the selectivity of the materials toward other rare earth elements and precious metals, like gold and silver, to be able to separate those from waste products as well.”
The work will be published in the November issue of Chemical Engineering Journal.
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