About the blog: What Things Are Made Of


The United States relies on imports for dozens of commodities in everyday use. Often enough, that reliance is 100%. In this book I aim to provide awareness of the hidden geology and mineralogy behind common things, and to develop an appreciation for the global resource distribution that underpins our society. While concerns about oil import reliance are in the news every day, our needs for other minerals are comparable and are typically unknown even to technologically aware Americans.

Monday, January 4, 2010

Yes, we have no aluminum (ore)

A friend questioned the quiz answer indicating that the U.S. is 100% dependent on imports for bauxite (photo, right), the only ore of aluminum. He knew that lots of minerals contain aluminum—it’s the third most abundant element in the earth’s crust, after oxygen and silicon. And the rock-forming minerals that contain aluminum are common, ranging from feldspars in granite to clays in fine-grained shale.

So why can’t the U.S. use those aluminum sources, rather than relying 100% on bauxite imports from Jamaica, Guinea, Brazil, Guyana, China, Sierra Leone, and Greece? The simple answer: It’s far too energy-demanding to get the aluminum out of any rock other than bauxite.

Despite aluminum’s abundance, aluminum metal was not isolated until 1825, by Danish chemist Hans Christian Oersted—the discoverer of the close relationship between electricity and magnetic fields. It was an electric current that allowed Oersted to produce impure metallic aluminum, but aluminum remained a rare and expensive curiosity for 60 years.

Charles Hall, a student at Oberlin College (Ohio) devised the first relatively cheap electrolytic aluminum manufacturing process in 1886—and the Aluminum Company of America treasured as “crown jewels” the small metal buttons Hall made.

Aluminum is bound tightly, usually with silicon, in common minerals. Only a few minerals lend themselves to the electrical disruption needed to free aluminum metal from the crystal lattices. Three aluminum hydroxide minerals, gibbsite, boehmite, and diaspore, are in that category, and they are the primary components of the rock bauxite. Bauxite forms by intense chemical weathering of aluminous minerals like feldspar in granite—in fact, Mother Nature does most of the work of producing aluminum, rearranging aluminum atoms to make bauxite’s hydroxides. Metallurgists seeking pure aluminum can process bauxite cheaply, while the aluminum in more common compounds like feldspar and clay is impossible to remove commercially.

In the United States, the only significant bauxite formed 90 million years ago in what is now Arkansas. Those deposits served as important ore sources from 1899 until competition from cheaper foreign markets and recycling ended production in 1990. The U.S. has no primary bauxite production today.

No bauxite doesn’t mean we don’t produce a lot of aluminum. With 30% recycling, together with processed imports, the United States in 2008 was a net aluminum exporter—a dramatic change from 2005 when metallic aluminum was imported (more than 40% of domestic consumption) along with 100% imported bauxite. U.S. aluminum smelters employ 55,000 workers in an industry whose metal production earns $7.9 billion each year.

As Jules Verne wrote, “Aluminum was once a precious metal.” Precious enough to cap the pyramid atop the Washington Monument in 1884, when aluminum’s price was $1 per ounce, the same as silver—at a time when a dollar bought nearly 500 pounds of coal, 150 bricks, or 15 pounds of flour.

Adapted and expanded from What Things Are Made Of, Chapter 4: You Are What You Eat. Bauxite image above from USGS via Wikipedia.

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