Source:Popular Mechanics
The viability of a renewable energy future relies on the ready supply of REEs, or rare-earth elements. There are 17 REEs in the periodic table and, though the name suggests otherwise, they are actually plentiful in the earth’s crust. The challenge is that these elements are not often concentrated in ore deposits, which makes them expensive and unreliable as an extractable resource for domestic use or export. This in part explains the shortage of these materials being extracted in the United States.
Two of these rare-earth elements, neodymium (Nd) and dysprosium (Dy), are crucial for the development of solar and wind technologies and electric vehicles, not to mention hard drives, television screens, and modern electronics like the one you may be holding in your hand right now. Yet according to Renewables Consulting Group (RCG), “the use of REEs has faced criticism due to price volatility and political issues surrounding the supply chain.” Add to that the millions of tons of acidic pollution generated by conventional extraction methods, and the renewable energy industry doesn’t look so green anymore.
Enter Paul J. Antonick and Zhichao Hu, members of the thermodynamics team at the Rutgers University School of Engineering, who contest that instead of using harsh chemicals to extract rare-earth elements, mineral and organic acids made by naturally occurring bacteria called Gluconobacter oxydanscould do the job instead.
The researchers used these natural acids along with a bio-acid mixture, or biolixiviant, to extract six rare-earth elements from synthetic phosphogypsum. The results, published in The Journal of Chemical Thermodynamics, showed that “the biolixiviant was more efficient at rare earth element extraction than gluconic acid and phosphoric acid but less efficient than sulfuric acid.”
Phosphogypsum is a waste by-product of phosphoric acid production. A Futurity article about the study states that “Each year, the U.S. mines an estimated 250 million tons of phosphate rock to produce phosphoric acid for fertilizers.” That’s a huge supply of phosphogypsum, representing roughly 100,000 tons of rare-earth elements ready for extraction. Currently, about 126,000 tons of REEs are produced worldwide. Tapping this resource at home would catapult U.S. production closer to China levels, which now account for 90 percent of the market share.
Researchers will soon test their bacteria-based extraction process on industrial phosphogypsum, which is more complex than lab-controlled samples. This is good news for large wind turbine manufacturers that rely on magnet generators made from neodymium and dysprosium, among other rare-earth elements like praseodymium (Pr) and terbium (Tb). Altogether, the use of REEs could result in the more efficient and reliable operation of renewable technologies.
Given the increase in demand for rare-earth metals, the question of how to recycle products made from them is also being considered. “With so many hundreds of thousands of tons of rare earth oxide being produced and manufactured into products each year,” says RCG’s Kerri Hart, “having recycling methods in place is a valuable contribution to keeping the costs of the materials low and maximizing the use of the rare earth elements.”