Tikalon Blog by Dev Gualtieri

Mass Quantities of Rare Earth

July 20, 2011

The coneheads were an entertaining part of the early episodes of Saturday Night Live . The coneheads were a not-very-well-disguised extraterrestrial family living in suburbia . The sketches featured Dan Aykroyd as Beldar, the father, Jane Curtin as Prymaat, the mother, and Laraine Newman as their daughter, Connie. They would deflect questions about their strange behavior, such as giving six-packs of beer as Halloween treats, by explaining that they did not know local customs, since they were from Remulak, a small town in France .

The coneheads had large appetites, probably as compensation for the metabolic heat lost from their large, bald heads. They would eat large quantities of food, an act they described as "consuming mass quantities." I happened to think about the coneheads when I read about a Japanese discovery of mass quantities of rare earth elements on the sea floor .

I wrote about the rare earths in a previous article (Rare Earth Shortage, June 21, 2010). The rare earth elements, which are are scandium , yttrium , and the fifteen lanthanides , are technologically useful in many ways. Advanced materials with rare earth content are used in the permanent magnets used in small motors and actuators, in catalysts , and in photovoltaics .

Their "rare" tag is somewhat of a misnomer, since the least abundant, thulium and lutetium , are more than a hundred times more abundant than gold . The real problem with the rare earths is that 95% are produced in China , which requires a larger share for its own industries.[1] This is worrisome to Japan , which imports large quantities of rare earths.[2]

Portrait by an unknown artist of Jöns Jacob Berzelius , co-discoverer of cerium , one of the rare earth elements.

(Via Wikimedia Commons).

A paper recently posted to Nature Geoscience by researchers at the University of Tokyo , the Japan Agency for Marine-Earth Science and Technology and the Tokyo Institute of Technology , reports on their elemental analysis of more than 2,000 seafloor sediment samples collected at 78 sites in a large part of the Pacific Ocean .[3] One sampled site in particular was so rich in the rare earths that a square kilometer would yield 20% of the current worldwide demand.[3]

As I've reported in a previous article (The Manganese Conspiracy, June 9, 2010), it's not unusual to find some elements to be highly concentrated in ocean deposits. The Japanese researchers find that hydrothermally created minerals , such as iron-oxyhydroxides and phillipsite , are enriched in rare earths. They were able to leach these minerals in acid to produce rare earth rich solutions.[3]

The minerals were found at depths of 11,500-20,000 feet (3,500 to 6,000 meters).[4] The rare earths aren't the only allure of seafloor sediment. A mining company called Nautilus has obtained a license to do seafloor mining of a sulfide mineral near Papua New Guinea . This sulfide is enriched in both copper and gold . There are, of course, growing environmental concerns.[4]

Is all this really worth the trouble, both environmentally and financially? The US has huge deposits of rare earths, but US production was halted because of the past availability of less expensive Chinese material. One interesting point is that the only large refineries for these ores are now located in China. Molycorp Minerals , which mines rare earth ore in the US, sends the ore to China to be refined.[5]

An article in the UK publication, The Register , throws a lot of cold water (pun intended) on the whole ocean mining of rare earths concept.[6] First, the concentrations are just a few thousand ppm , at best,or about a kilogram per metric ton . Second, not only are the deposits at the bottom of the ocean, but most lie below an overlayer of ten meters of other silt. That's a lot of material to move around. There's the further capital expense of the refining operation.

If your back's against the wall, as the case may be for Japan because of its strained political relations with China, it might just be necessary. However, if I were a Japanese businessman, I would invest in mines and refineries in the United States, instead.

The rare earths are chemically very similar to each other, so how are they separated? The current process involves complexing and ion-exchange via an ion-exchange resin . This method was invented by Frank H. Spedding and colleagues at Ames Laboratory .[7] The first claim from their 1957 patent is as follows:[7]

1. A process of separating a plurality of rare earth metal values contained in an aqueous solution from each other, comprising contacting said solution with a nonacidic cation exchange resin whereby said rare earth metal values are adsorbed on said resin; contacting said resin with an aqueous solution of an ethylenediamine tetraacetic acid agent having a pH value of at least 5 for a sufficiently long period of time to allow equilibration, the amount of said ethylenediamine tetraacetic acid agent being less than the stoichiometric amount required to complex all of the rare earths adsorbed on said resin; and separating the resin containing the noncomplexed rare earth values from the solution containing the complexed rare earth values.

Mass Quantities of Rare Earth

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