The Rare Earths
By Larry Larason
You’ve probably heard of “Peak Oil.” That’s the idea that we’ve used more than half of the world’s petroleum and now production is beginning a steady decline. Well, we seem to have averted that, at least temporarily, by horizontal drilling and fracking. But it’s only one of several doomsday scenarios in the wind. Such predictions go back at least to 1798 when Thomas Malthus published his essays proposing that human populations were increasing beyond the ability of agriculture to produce food to feed them. He foresaw famine and disease in the near future. I remember, in the 1960s and ’70s, books like the Club of Rome’s Limits to Growth, about how the world was running out of stuff, and Paul R. Ehrlich’s The Population Bomb, which echoed Malthus in many ways. None of the dire predictions in those books came to pass . . . yet.”]”I’m sure that there have been many more similar doomsday predictions but I don’t want to try to look up all of them. One of the most recent was brought about by some squabbles with China. Here’s a simplified version of the story. The Mountain Pass Mine in California had been a major supplier of rare earths elements until a mine in China began production and, with its low labor costs, undercut the prices of the American supplier. Mountain Pass was also facing some environmental problems, so it shut down in 2002, giving China a near monopoly. In 2010 China set up export quotas for rare earths, then later, stopped exporting rare earths to Japan over a dispute about fishing grounds. This caused a bit of panic in world markets, because rare earths have become so critical in high tech applications. The China scare prompted Molycorp to reopen the Mountain Pass Mine last year, and American mining companies are exploring for new deposits to assure than we have our own sources of rare earths.
So what are the rare earth elements? In the periodic table of elements you generally find them in a separate row, below and detached from the rest of the table. They range from lanthanum [La] to lutetium [Lu], with atomic numbers from 57 to 71. Scandium [Sc] and yttrium [Y] are generally included in the group, although they appear in column 3 of the table and have atomic numbers of 27 and 39, respectively. That’s a total of 17 elements. At the time most of them were discovered they were known to occur in only one place in the world – at a porcelain mine near Ytterby, Sweden. [That’s pronounced it-er-bee.] Seven of the 17 rare earths were discovered in rocks from Ytterby and several named for the locale: ytterbium [Yb], yttrium [Y], terbium [Tb] and erbium [Er]. Now we know that they are not so rare – cerium [Ce], for example, is more common in the Earth’s crust than copper – and chemists prefer to call them lanthanides, although the term “rare earths” is still a synonym.
Although we know they are not that rare, they seldom occur in deposits concentrated enough for economical mining. Also, they usually occur together. They are all chemically similar and, thus, are difficult to separate and purify. Some isotopes are mildly radioactive. Some deposits are “contaminated” with strongly radioactive thorium, so the ore is considered undesirable for mining.
So why are the lanthanides so important? Here are just some of the uses. Without europium in the phosphors on your television screen the reds would not be as vivid and without terbium the greens would be tepid. Rechargeable batteries depend on rare earths. Every Toyota Prius on the road has about 20 pounds of lanthanum in the batteries, although because of price increases for that element, Toyota is looking for substitutes. Scandium [Sc] is used to strengthen bicycle frames and aluminum bats. Various lanthanides are used in X-ray machines, catalytic converters, lasers, fiber optics, and LED light bulbs.
Probably the most important role for lanthanides is in the field of magnetism. To me, magnetism is spooky. Science can tell us how it works, but not necessarily why. Still, we use it everyday and rely on it in many of our devices. For example, you can’t have speakers for announcing ball games or hearing someone on your cell phone without magnets.
Somewhere around the house I still have an alnico magnet that my dad picked up sometime in the 1950s, probably as a curiosity. Plucking it off a steel panel is almost a two-handed operation. The name comes from the alloy of aluminum, nickel, cobalt, and iron. Until recently it was the strongest permanent magnet compound known. It’s hard to imagine that today’s rare earths magnets are five time stronger!
In a cell phone the magnet for the speaker needs to be small enough to fit in the chassis of the pocket sized phone. Only lanthanide magnets have enough power at that size. Similarly, for wind turbines you need powerful magnets to generate more electricity, but they can’t weigh too much or you would have to build a stronger, more expensive pylon to support the turbine. Again, lanthanides come to the rescue. Some of the larger turbines contain up to 700 pounds of neodymium [Nd].
So are we going to run out of lanthanides? The supply is skimpy and the demand is rising along with the prices, but reserves are still in the ground. And, for some good news: New Mexico has lanthanides. Six mining districts in our state have produced ores in the past, and a report from the New Mexico Bureau of Geology and Mineral Resources in the summer of 2011 stated that several mining companies were exploring deposits around the region. Exploration and permitting procedures may take many years, but we might have a lanthanide mine in New Mexico sometime in the next decade or two.
You may not have heard of the lanthanides before, but they are already important and new uses are being discovered all the time. They are almost sure to be increasingly in the news.
I sort of made fun of doomsday stories, but I’m not really unconcerned. Global climate change, for example, has me worried; last summer was miserable. The National Climatic Data Center recently said that July of 2012 was 3.2 degrees warmer than the average for the entire twentieth century. I also feel that our huge population is straining our resources. Don’t get complacent; one of the doomsday scenarios is going to bite us at some point in the future.