Rare earth elements plentiful in ocean sediments

Economically vital metals could be mined from deep sea, Japanese geologists propose

Mud at the bottom of the Pacific Ocean contains surprising concentrations of rare earth elements, 17 chemicals with exotic names like neodymium and europium that are critical to technologies ranging from cell phones and televisions to fluorescent light bulbs and wind turbines.

Hot plumes from hydrothermal vents pulled these materials out of seawater and deposited them on the seafloor, bit by bit, over tens of millions of years. One square patch of metal-rich mud 2.3 kilometers wide might contain enough rare earths to meet most of the global demand for a year, Japanese geologists report July 3 in Nature Geoscience.

“I believe that rare earth resources undersea are much more promising than on-land resources,” says Yasuhiro Kato, a geologist at the University of Tokyo who led the study.

More than 97 percent of the world’s rare earth elements come from mines in China, which has restricted exports in recent years. With prices skyrocketing, shortages are feared — especially in Japan, which lacks minable deposits of these elements.

Kato’s team analyzed seafloor cores taken from 78 sites throughout the Pacific Ocean. Near Hawaii and in the southeast Pacific, concentrations of rare earths were comparable to those found in clays mined in China. Some deposits contained twice as much heavy rare earths such as dysprosium, a component of magnets in hybrid car motors.

“The heavier rare earths tend to be ones that command greater price because of their scarcity,” says Alex King, director of the U.S. Department of Energy’s Ames Laboratory in Iowa.

Deep-sea mining is an old idea, but one that has yet to prove itself in the face of high costs and environmental concerns. Discovered decades ago, chunks of manganese on the ocean floor and deposits of metals such as zinc and copper in the Red Sea have proven impractical to mine.

“I don’t understand how this can be expected to be an economic way to recover rare earth,” says Daniel Cordier, a mineral commodity specialist at the U.S. Geological Survey’s National Minerals Information Center in Reston, Va.

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