Published on August 2nd, 2013 | By: Eileen De Guire0
Is there praseodymium in them thar hills?Published on August 2nd, 2013 | By: Eileen De Guire
The hunt for rare earth sources includes finding new sources, reclaiming mine tailings, and extracting them from discarded electronics. Here, Ames Laboratory researchers apply physical metallurgy principles to extracting rare earths from recycled components. Credit: Ames Lab.
When it comes to mining rare earth minerals, there is no “low hanging” fruit. Their name, “rare earths” belies the truth—they are not so much rare as they are mighty difficult to get at.
According to a United States Geological Survey fact sheet from 2002, “abundant” REs, such as lanthanum and cerium, are as plentiful in the Earth’s crust as are common industrial metals such as chromium, nickel, copper, zinc, molybdenum, tin, tungsten, and lead. The fact sheet notes that the two least abundant of the RE elements—thulium and lutetium—are almost 200 times more common than gold. (Strictly speaking, REs comprise the 15 elements in the lanthanide series of the periodic table. However, scandium and yttrium are generally included in the RE category because they tend to be found in the same deposits and have some similar chemical properties.)
The problem is that REs tend not to concentrate in easy-to-mine deposits. (You’re not likely to hear “There’s praseodymium in them thar hills, boys!”—reminiscent of the legendary call-to-action for 19th century gold rush miners.) The vast majority of rare earth ores come from China, but political and economic factors, combined with escalating demand, have led to supply and cost instability. Last year, a large deposit of neodymium was discovered in Brazil, and in the United States, Molycorp is reactivating its Mountain Pass mining and ore processing operations.
In an ironic twist, gold rush miners may well have mined rare earths a century-and-a-half ago in their quest to get to the glittering gold veins embedded in the rock.
Last week an Associated Press story hit the internet about USGS research on the mine tailings from abandoned gold, silver, and copper mines. It is well known that USGS and the Department of Energy have made RE recovery and recycling research priorities. Also, increasingly more research resources are supporting the search for alternatives to rare earth components based on non-RE compositions.
According to the story, the USGS Central Mineral and Environmental Resources Science Center (Denver, Colo.) is working with scientists at the University of Nevada–Reno and the Colorado School of Mines to evaluate abandoned mine tailings. Ultimately, the goal is to compile a database to identify where there might be a “mother lode” of mine tailings for RE extraction.
The USGS team uses laser ablation technology combined with plasma mass spectrometry to analyze rock chemistries. Alan Koenig, the USGS scientist leading the tailings project, says in a USGS news story, “I get to shoot rocks with lasers to discover new (or old) information about rare metals contained within the rock. We can tease out from the rock not only what it’s made of, but we can discover a story about how it formed.” The laser ablation approach has the advantage of determining rock chemistry directly and avoids time-consuming or acid-based extraction methods.
However, even if mine tailings prove to have significant RE content, that still leaves the problem of extracting the metals, as MetalMiner blogger Stuart Burns observes. He writes that it takes “extensive high-technology refining facilities that can turn a 3% compound in the rock into a 100% pure oxide useable by industry.” And extraction and refining, he points out, are key to the economic viability of Molycorp’s Mountain Pass facility (shown in the image above).
Meanwhile, rare earth deposits have been discovered in the Bokan Mountain region of Alaska where uranium used to be mined. The discovery is significant because of the unusual abundance of the heavier REs, which are not only harder to find but more useful for technology. USGS geologists hope their studies of the geology of Bokan Mountain will teach them what to look for when hunting for other potential RE deposits.
Besides finding more naturally occurring RE sources, DOE’s newly established Critical Materials Institute in Ames, Iowa, is coordinating research into alternatives to rare earths, as well as recycling technologies. CMI just released its first report, which outlines the institute’s four strategic thrusts: diversifying supply, developing substitutes, improving reuse and recycling, and crosscutting research. (This last item includes enabling science, sustainability, supply chain, and economic analysis.)
This video describes one approach Ames Lab scientists are trying for recycling rare earths. Similar to the problem of ore beneficiation, extracting the RE from the discarded component is the crux of the problem.
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