To help increase the U.S. supply of rare earth metals, a Lawrence Livermore National Laboratory (LLNL) team has created a new way to recover rare earths using bioengineered bacteria.
Rare earth elements (REEs) are essential for American competitiveness in the clean energy industry because they are used in many devices important to a high-tech economy and national security, including computer components, high-power magnets, wind turbines, mobile phones, solar panels, superconductors, hybrid/electric vehicle batteries, LCD screens, night vision goggles, tunable microwave resonators -- and, at the Laboratory, the National Ignition Facility's neodymium-glass laser amplifiers.
More than 90 percent of the global REE supply comes from China.
"To alleviate supply vulnerability and diversify the global REE supply chain, we’ve developed a new extraction methodology using engineered bacteria that allowed us to tap into low-grade feedstocks," said Yongqin Jiao, lead author of a paper appearing in the journal, Environmental Science & Technology.
"Non-traditional REE resources, such as mine tailings, geothermal brines and coal byproducts, are abundant and offer a potential means to diversify the REE supply chain. However, no current technology exists that is capable of economic extraction of rare earths from them, which creates a big challenge and an opportunity."
A Department of Energy (DOE) report said in 2011 that supply problems associated with five rare earth elements (dysprosium, terbium, europium, neodymium and yttrium) may affect clean energy development in coming years.
Many recent studies have looked at the use of biomass for adsorption of REEs. However, REE adsorption by bioengineered systems has been scarcely documented, and rarely tested with complex natural feedstocks.
But in the new research, the LLNL team recovered rare earth elements from low-grade feedstock (raw material supplied to a machine or processing plant) using engineered bacteria.
Through biosorption experiments conducted with leachates from metal-mine tailings and rare earth deposits, the team showed that functionalization of the cell surface yielded several notable advantages over the non-engineered control. The team saw significant improvements in adsorption efficiency and selectivity for REEs versus other non-rare earth metals.
Microbial mediated surface adsorption (biosorption) represents a potentially cost-effective and ecofriendly approach for metal recovery. Microorganisms exhibit high metal adsorption capacities because of their high surface area per unit weight and the abundance of cell surface functional groups with metal coordination functionality. Additionally, the reversibility and fast kinetics of adsorption enables an efficient metal extraction process, while the ability of cells to withstand multiple adsorption-desorption cycles avoids the need for frequent cell-regeneration, decreasing operational costs. Biosorption also is expected to have a minimal environmental impact relative to traditional extraction techniques.
"Our results demonstrate the technical and economic feasibility of coupling bioengineering with biosorption for REE extraction from low-grade feedstocks," Jiao said.
The rare earths comprise 17 elements in the periodic table -- scandium, yttrium and the 15 lanthanides (lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium). Despite their name, the rare earths (with the exception of promethium) are not all that rare, but are actually found in relatively high concentrations across the globe. However, because of their geochemical properties, they seldom occur in easily exploitable deposits. All REEs occur together and require extensive chemical processing (traditionally) to isolate the individual REEs. Using bacteria in the new research can provide a disruptive alternative to current methods.
The work is part of the Critical Materials Institute, a DOE Innovation Hub led by the DOE’s Ames Laboratory and supported by DOE's Office of Energy Efficiency and Renewable Energy's Advanced Manufacturing Office. CMI seeks ways to eliminate and reduce reliance on rare-earth metals and other materials critical to the success of clean energy technologies.
Other Livermore researchers include Dan Park, Lawrence Scholar Aaron Brewer and colleagues from the University of Washington, Idaho National Laboratory and the University of California, Berkeley.
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