Such a difficult production process is one reason why the U.S. no longer mines them. Until the 1990s, the U.S. was the major supplier of rare earths, largely out of one mine in Mountain Pass, Calif., owned by oil company Unocal, now part of Chevron. Unocal shut down that mine—and processing facility—in 2002 because they could not compete with China's purer product that began to flood the market in the 1990s. Unocal "didn't think there would be a need for high-purity products," explains chemist John Burba, chief technology officer for Molycorp, the company hoping to reopen rare earth production at the Mountain Pass Mine.
Plus, the operations were not exactly environmentally friendly. "Back in the 1990s the plant was sending 850 gallons of wastewater per minute down a pipeline into evaporation ponds," Burba notes. "It was a devil's mixture because of the chemistry they employed." In addition, the rare earths at Mountain Pass are mixed with radioactive thorium, requiring special care in handling and disposal.
The whole slew of rare earth elements are a challenge to separate because of their chemical similarity—and they are never found alone. "The challenge with rare earths is they always occur together," GE's Iorio explains. "There are processing costs to separate them out from each other."
Regardless, the Chinese National Offshore Oil Corp. (CNOOC) wanted to purchase Unocal—and its California rare earth asset—in 2005, a move the U.S. military blocked, according to Burba. Now Molycorp wants to restart operations by 2012 using a new process, which will require Molycorp to essentially rebuild the entire operation at a cost of $500 million. The process employs a strong acid and a base to separate the rare earths—the so-called chlor–alkali solvent extraction method—but it still will not produce pure rare earths; rather it will yield oxides of cerium, lanthanum, praseodymium and neodymium.
In essence, Mountain Pass will become a chemical plant, sucking up electricity and steam from an on-site natural gas–fired boiler. In addition, the wastewater of the process will be recycled back to produce the strong acid and base necessary to start the process all over again—hydrochloric acid and sodium hydroxide. "Mining is a very small part of our operation," Burba says, noting that mining the ore containing the rare earths is only 10 percent of his company's cost. "The vast majority of what we do is advanced chemistry."
Of course, there will still be by-products—such as the residual ore, or tailings, from the mining and separation as well as calcium carbonate, magnesium carbonate and magnesium hydroxide from the chemical process, along with that pesky thorium. But the primary salt from the chlor–alkali process is sodium chloride (otherwise known as table salt), which will be recycled back into the process using some of the steam generated on site and use to make new acid and base using a chlor-alkali unit. "It's a big saltwater loop," Burba explains. "Our water consumption is 10 percent or less of what had been done historically at this site."
By next year, the site hopes to produce 2.7 million kilograms of rare earth oxides a year—separating the elements from the ore using a liquid ion-exchange process. By 2015, they hope to be at full production, producing 18 million kilograms of various rare earth oxides a year. "We have greater than 30 years of mining capacity at 40 million pounds per year," Burba says.
But that only represents 6 percent of the present global market, which is still growing. The U.S. Government Accountability Office estimates it will take seven to 15 years to find new rare earth deposits, build the infrastructure to process them, and make them available to manufacturers. "This is not like going out and panning for gold," Burba notes. "This processing requires a huge amount of chemical processing. You have to have good infrastructure."