MetalMiner has long reported on product developments within the metals industry. Years ago, (okay, we’re not that old, 7 years ago), my colleague Stuart Burns discussed several types of rare earth extraction processes that would enable rare earths recycling.
At the time, all 3 processes lacked commercial viability for several reasons – typically because of cost or not yielding pure metals on the back end or both.
Today, a team of researchers at Worcester Polytechnic Institute may have developed both a technically viable means for recycling rare earths – specifically neodymium, dysprosium and praseodymium from the drive units and motors of discarded electric and hybrid cars – as well as a commercially viable one.
Current Recycling Extraction Processes
According to my colleague Stuart, 3 extraction processes (the methods of pulling rare earths apart from other metals) exist:
- Aqueous-based technology: It produces mixed metal oxides or fluorides, which are then as expensive as the original ore to refine.
- Electro-slag refining: Works well for large clean pieces of scrap, but less well for contaminated or fine grit. In addition, the transition metals often get pulled across into the end product, which then requires extensive additional refining to access the REs.
- Liquid Metal Extraction: a process that offers some promise because it can accept multi-metal inputs and distinct metal outputs, but has not been developed commercially for REs. However, it has worked for silver extraction from lead ores, so the basic technology is understood.
The research team at Worcester Polytechnic Institute has developed a methodology that makes aqueous-based technology potentially viable.
In an interview with MetalMiner, WPI Professor Marion Emmert described the process she and her colleagues developed.
“With motors we have a bunch of different materials – magnets, steel and copper, and often we don’t know the alloy of steel,” Emmert said. “The process we’ve developed enables us to separate the rare earth materials selectively from all of the other materials in the motor.”
There are several elements to this process.
“First, we pre-heat the motors to get rid of the magnetism,” Emmert explained. “|Next, we have developed a materials mixture that dissolves the magnet material so you can put the other metals into a regular recycling stream. Next, we add another reagent to the obtained mixture of rare earths plus iron (a dark black solution containing the metals as aqueous salts) that creates a white powder that contains only rare earth oxalates. We are achieving more than an 80% recovery rate because the solutions or mixtures we have developed are very selective.”
Part of the science, according to Emmert, involves the fact that rare earths are inherently reactive with oxygen and water.
Emmert subjects the solution coming out of this process (containing iron hydroxides, boronic acid and traces of rare earth hydroxides) to pyrohydrolysis, a process that is well established in steel pickling. This allows for the recovery of the acid used in the first step, making the process more sustainable and closed loop. The result is solid iron oxides, boron oxides, and traces of rare earth oxides. This solid can then be sold to the iron ore processing industry.
Emmert knows the technology and processes she and her team have developed aren’t as cost effective as mining, say, neodymium. However, as regions such as Europe deploy regulations requiring automakers to build cars with a minimum percentage of recycled products, a fee-based model could work and help automakers and OEMs meet the more stringent regulations.
To learn more about the separation technology, please visit: Engines of Change: WPI Team Recovers Rare Earth Elements From Discarded Motors of Electric and Hybrid Vehicles. Please follow Lisa Reisman on Twitter @LReismanMM