Source: Phys.org | Dawn Levy, ORNL| August 14, 2019
Rare earth elements are the “secret sauce” of numerous advanced materials for energy, transportation, defense and communications applications. Their largest use for clean energy is in permanent magnets, which retain magnetic properties even in the absence of an inducing field or current.
“We have developed an energy-efficient, cost-effective, environmentally friendly process to recover high-value critical materials,” said co-inventor Ramesh Bhave of DOE’s Oak Ridge National Laboratory, who leads the membrane technologies team in ORNL’s Chemical Sciences Division. “It’s an improvement over traditional processes, which require facilities with a large footprint, high capital and operating costs and a large amount of waste generated.”
Permanent magnets help computer hard drives read and write data, drive motors that move hybrid and electric cars, couple wind turbines with generators to make electricity, and assist smartphones to translate electrical signals into sound.
Through the patented process, magnets are dissolved in nitric acid, and the solution is continuously fed through a module supporting polymer membranes. The membranes contain porous hollow fibers with an extractant that serves as a chemical “traffic cop” of sorts; it creates a selective barrier and lets only rare earth elements pass through. The rare-earth-rich solution collected on the other side is further processed to yield rare earth oxides at purities exceeding 99.5%.
That’s remarkable considering that typically, 70% of a permanent magnet is iron, which is not a rare earth element. “We are essentially able to eliminate iron completely and recover only rare earths,” Bhave said. Extracting desirable elements without co-extracting undesirable ones means less waste is created that will need downstream treatment and disposal.
Supporters of the work include DOE’s Critical Materials Institute, or CMI, for separations research and DOE’s Office of Technology Transitions, or OTT, for process scale-up. ORNL is a founding team member of CMI, a DOE Energy Innovation Hub led by DOE’s Ames Laboratory and managed by the Advanced Manufacturing Office. Bhave’s “mining” of an acidic solution with selective membranes joins other promising CMI technologies for recovering rare earths, including a simple process that crushes and treats magnets and an acid-free alternative.
Industry depends on critical materials, and the scientific community is developing processes to recycle them. However, no commercialized process recycles pure rare earth elements from electronic-waste magnets. That’s a huge missed opportunity considering 2.2 billion personal computers, tablets and mobile phones are expected to ship worldwide in 2019, according to Gartner. “All of these devices have rare earth magnets in them,” Bhave noted.
Bhave’s project, which began in 2013, is a team effort. John Klaehn and Eric Peterson of DOE’s Idaho National Laboratory collaborated in an early phase of the research focused on chemistry, and Ananth Iyer, a professor at Purdue University, later assessed the technical and economic feasibility of scale-up. At ORNL, former postdoctoral fellows Daejin Kim and Vishwanath Deshmane studied separations process development and scale-up, respectively. Bhave’s current ORNL team, comprising Dale Adcock, Pranathi Gangavarapu, Syed Islam, Larry Powell and Priyesh Wagh, focuses on scaling up the process and working with industry partners who will commercialize the technology.