Diversify, replace, recycle
Energy labs and partners come together to ensure supplies of critical energy materials
ORNL materials scientist Orlando Rios works with a high-field processing magnet that uses both radio frequency heating and a strong magnetic field to alter the microstructure of materials to improve their magnetic properties. Photo: Jason Richards
ORNL materials scientist Michael McGuire covers the other end of the thermal spectrum with a liquid helium-cooled physical-properties-measuring system that also employs an intense magnetic field to synthesize and measure the properties of alternative magnetic materials. Photo: Jason Richards
Across the US, energy labs are working to turn a widespread shortage of critical energy materials into a boon for domestic mining and clean energy industries.
The US Department of Energy's new Critical Materials Institute, led by Ames Laboratory, brings together experts from ORNL, Idaho National Laboratory, Lawrence Livermore National Laboratory, seven universities, and seven industrial partners.
ORNL chemist Bruce Moyer, who leads CMI's effort to diversify the supply of critical materials, explains that the institute is focused on ensuring the availability of materials that support clean energy technologies— particularly rare earth elements that are critical to producing electric vehicles, wind turbines, solar energy, batteries and energy-efficient lighting. He notes that DOE's 2011 Critical Materials Strategy identified five rare earth metals (dysprosium, terbium, europium, neodymium and yttrium) whose availability could affect clean energy technology deployment in coming years.
Two of these, dysprosium and neodymium, are particularly critical to the production of the strong magnets used in electric motors. Without them, magnets would be weaker, and products such as electric vehicles and wind turbines would be less efficient and too costly to operate.
Beyond the rare earth elements for magnets, CMI is also addressing supply issues related to phosphors—compounds which often depend on the very scarce rare earth metals europium, terbium and yttrium and are used in energy-efficient lighting. Another CMI focus is on potential shortages of two elements DOE describes as "nearcritical": lithium, because of its importance to battery manufacturing, and tellurium, for the role it plays in solar panel production.
"There are three main ways to approach the challenge of ensuring that we have the materials we need," Moyer says. "One is to diversify the supply. The second way is to find substitutes, and the third way is to develop technologies for recycling. ORNL is most heavily involved in investigating the first two for CMI, though we do have activities taking place in developing recycling technologies as well as in developing new computational tools to accelerate the molecular design of new separation agents."
An innovative example of diversifying the supply of a key material, in this case lithium, can be found in California's Imperial Valley, where six power plants are using superheated geothermal brines from deep underground to generate steam for the production of electricity. The lithium-rich brine would normally then be pumped back into the ground; however, CMI industrial partner Simbol Materials is working with the utility to re-route the brine through a process that extracts lithium before the liquid is recycled. ORNL's chemical separations expertise is helping Simbol increase the efficiency of its extraction process, which is currently being run on a relatively small "pilot" scale.
"We plan to work with Simbol to develop new separation materials, sorbent materials and membranes that are lithium-selective," Moyer says.
Efforts to improve the supply side of the equation for rare earths aim to find new sources, which then could enhance mineral processing efficiency and encourage the development of new uses for the more abundant rare earth metals.
Moyer explains that when ore containing rare earth minerals comes out of the ground, the rare earths make up a very small fraction of the material. The key challenge becomes separating the 1, 5 or 10 percent of the ore that contains rare earth metals from the rest of the rock. Then the resulting "concentrate" can be economically processed to recover and purify the individual rare earth elements.
"One of our most exciting projects combines ORNL's strengths in the dynamics of mineral interfaces and molecular design with Colorado School of Mines' strength in mineral processing to develop new froth flotation agents to concentrate rare earth minerals from ore," Moyer says.
In froth flotation, crushed and ground ore particles are mixed with water and detergentlike molecules called "collectors," which attach themselves very selectively to the surfaces of the desired mineral particles in the mixture— rare earth minerals, in this case. Air is then bubbled through this mixture to create froth.
"We can adjust the chemistry of the flotation agent so the particles we're interested in stick to the bubbles and the others are washed away," Moyer says. "Despite the apparent simplicity of this technique, advancing the technology will require expanding the limits of interfacial science and molecular design."
Moyer and his colleagues are working with the mining chemical company Cytec and the mining company Molycorp to apply this technique to the task of improving Molycorp's mining operations.
"Our first goal is to develop a new flotation agent and process chemistry that will help our partners increase their recovery of the rare earths from the ore," Moyer says. "This project is being led by Colorado School of Mines."
ORNL's flotation agent design team includes experts on characterizing the structure and dynamics of mineral-water interfaces, as well as chemical scientists who are designing new flotation agents that can selectively bind to the surface of the bubbles as well as to the rare-earth-containing particles. Once new agents have been developed, Moyer's team will send them to the Colorado School of Mines for testing. The most effective ones will be passed along to ORNL's partners at Cytec to enable them to produce and test the agents in larger quantities.
"Our hope is that Molycorp will think this process looks attractive and will want to conduct a large-scale test at its facility," Moyer says.
CMI's program to develop alternatives to rare earth materials includes efforts to devise magnetic materials that use fewer rare earth materials, as well as new phosphors that, ideally, don't use any. Brian Sales, an ORNL materials scientist and deputy head of the program, explains that critical materials aren't just a problem for the future; they're part of everyday life. He notes there are a billion or more fluorescent lights in use, and the phosphors in each of them contain a substantial amount of rare earth material.
The institute's search for alternatives to rare earth materials benefits from its interdisciplinary perspective. Materials theorists often work with computational scientists and materials scientists to develop potential solutions. The result is an ongoing cycle of theory, computation and laboratory research. This may seem redundant, but it moves researchers steadily toward their goals.
"As laboratory scientists we take suggestions from theorists and computational simulations all the time," Sales says. "Generally, they can't point us in a specific direction or at a specific combination of materials. Their guidance is more like a compass than a GPS system. That's why this kind of research has to be an iterative process."
Sales suggests that alternatives to rareearth- containing phosphors might be found in the next two or three years. "Of course, it will take a while longer than that before they're implemented by industry," he says.
"We have been very pleased with General Electric's enthusiasm. They will be testing the materials we've come up with at their Cleveland plant. I think substitute materials for phosphors probably have the best chance of making a real impact in the next few years."
Substitute materials for magnets, he suggests, have real possibilities but will probably take a bit longer. "A lot of research organizations have been working on this," Moyer says. "It's a much harder problem, so we'll have to come up with some novel approaches."
CMI is operating on five-year timeline for success. Moyer emphasizes that the institute will measure its success or failure in terms of the impact of its technologies on the supply of critical materials.
"You have to work closely with industrial partners to do this kind of thing," he says. "If industry doesn't use our technology, then it won't have an impact, and it won't do a thing to reduce material criticality. However, if we develop a technology and industry uses it to increase the supply of these materials, then we can say that CMI really made something happen." —Jim Pearce