Scientists find new way to recycle REE

As rapidly advancing technology leaves behind printed circuit boards, old computers, obsolete televisions, and other electrical devices, mountains of electronic waste, or e-waste, being stockpiled around the world is becoming a major environmental concern.

Considered the fastest-growing waste stream in the developed world, scientists and policymakers worry that these end-of-life products are spawning environmental contamination and seepage into the world's food chain.

Others, however, are recognizing opportunities to recycle the mushrooming source of high-demand metals and minerals, including rare earths, in the world's growing stockpiles of e-waste.

Electronic waste, however, requires specialized methods of recycling because of the toxic nature of high-tech materials. But current methods of recycling these materials have made disposing of e-waste responsibly an expensive venture for industrialized countries.

As a result, the burden of recycling is being transferred to the developing world, where environmental protections are lax and the necessary technologies to safely extract materials do not exist, according to ScienceDirect.com.

In Third World countries, stockpiles of this potentially toxic trash are even open to the public for scavenging by low-income families and their children. The result is a worsening phenomenon worldwide of environmental contamination and negative health effects, the website said.

The magnet mineral

Extracting at least one critical mineral, the rare earth element neodymium, from e-waste stockpiles around the globe in an environment-friendly way that is both economical and effective just got easier, thanks to a process developed by researchers at Pennsylvania State University.

Rare earths, meanwhile, have become exceedingly critical in advanced industries. Yet, despite the high demand for this suite of technology elements, the world is still experiencing a shortage in ready-to-exploit resources, environmentally friendly processing, and reliable recovery strategies, rendering sustainable REE removal an immediate and unmet challenge worldwide, the researchers said.

Neodymium is a rare earth element that belongs to the lanthanide series and is used to create the strong magnets found in electric vehicle motors, aircraft generators, loudspeakers, hard drives, and in-ear headphones.

With the symbol Nd and atomic number 60, neodymium is not found naturally in metallic form or unmixed with other lanthanides, and it is usually refined for general use. Although neodymium is classed as a rare earth element, it is fairly common – no rarer than cobalt, nickel, or copper, and is widely distributed in the Earth's crust.

Extracting neodymium from e-waste

Led by Amir Sheikhi, assistant professor of chemical engineering and biomedical engineering, the researchers at Penn State developed a new nanotechnology that separates neodymium from other substances using plant cellulose found in paper, cotton, or wood pulp.

In the January 2022 edition of the Chemical Engineering Journal, Sheikhi and co-authors Patricia Wamea, Mica Pitcher, and Joy Muthami describe their innovation in a research article: "Nanoengineering cellulose for the selective removal of neodymium: Towards sustainable rare earth element recovery."

Hairy cellulose nanocrystals, nanoparticles derived from cellulose fibrils, bind selectively to neodymium ions, separating them from other ions, such as iron, calcium, and sodium, according to Sheikhi. The nanoparticles are "hairy" due to cellulose chains attached to their two ends, which perform critical chemical functions.

"We nanoengineered cellulose, the most abundant biopolymer in the world, to develop a sustainable bio-based technology named 'anionic hairy nanocellulose' for the high-capacity and selective removal of neodymium ions, one of the most widely used REE, from aqueous media," Wamea wrote in the research paper.

The anionic hairy nanocellulose comprises fully solubilized dicarboxylated (dissolved dicarboxylic acid salts) cellulose chains and cellulose nanocrystals decorated with dicarboxylated hairs bearing a charge density that is about one order of magnitude higher than conventional cellulose nanocrystals.

The unique colloidal properties of the anionic hairy nanocellulose, particularly the polyanionic hairs, enable the removal of roughly 264 milligrams (give or take 14mg) of neodymium ions per gram of the nano-adsorbent within seconds. The Penn State scientist said this ranks the advanced material among the adsorbents with the highest removal capacity at the shortest contact time that it is aware of.

Combined with the biorenewability of cellulose and a low operating cost, this technique offers a promising sustainable nanotechnology for removing neodymium ions from industrial wastewater, mining tails, e-waste, and neodymium-iron-barium permanent magnet leachates.

Fast, effective process

The researchers negatively charged the hairy layers of the nanoparticles to attract and bind with the positively charged neodymium ions, resulting in particle aggregation into larger pieces that can then be effectively recycled and reused.

"The process is effective in its removal capacity, selectivity and in its speed," Sheikhi observed. "It can separate neodymium in seconds by selectively removing the element from some of the tested impurities."

He also said current rare earth element recycling processes are environmentally detrimental. They often use highly acidic conditions to extract the elements in chemical reactions.

He said the process developed by his team is environmentally friendly due to its use of cellulose, which is an inexpensive renewable resource.

"Using cellulose as the main agent is a sustainable, cost-effective, clean solution," Sheikhi said. "Using this process, the United States will be able to compete with other giants like China to recover rare earth materials and independently produce them."

China is the leading exporter of neodymium, exporting more than 70% of the world's supply of the material.

Neodymium is a rare earth element and one of 50 minerals the U.S. government has designated as being "critical" to its national security.

In addition to e-waste, rare earth elements like neodymium can be extracted from industrial wastewater, mining tails, and permanent magnets that are no longer in use. In the future, Sheikhi said he hopes the cellulose-based adsorption process can be applied to those sources as well. Unlike absorption, where a material takes in a liquid or gas, adsorption enables a material to collect a liquid or gas on its surface.

"This contribution to rare earth recycling will have a strategic and economically-viable impact on several industries," Sheikhi predicted. "The more neodymium we recycle, the more we can manufacture electric and hybrid vehicles and wind turbines, leading to less strain on the environment."