Many useful metals unearthed from U.S. mines are discarded.
When mining operations dig for valuable metals, they often exhume ore containing other metals too. These by-product elements are usually treated as waste, but recovering even small fractions could offset the need to import them, researchers report August 21 in Science. For instance, recovering just 1 percent of rare earth elements from this material could replace imports.
“We’re used to skimming cream off the top,” says Elizabeth Holley, a mining geologist from the Colorado School of Mines in Golden. “We need to be better at recovering more from what we’re using.”
Ore often contains a medley of minerals and metals, but it’s not always profitable or feasible to extract them all. Some mining operations do recover certain by-product metals alongside their target metals: Platinum-palladium mines in Montana, for example, recover nickel and cobalt. But by-products are often discarded into waste sites, where they become more challenging to extract. Meanwhile, the United States spends hundreds of billions of dollars annually to import them.
Mining geologists often try to assess the amount of metal in a mineral deposit, but that doesn’t address the rocks already unearthed but not yet discarded, Holley says. The new study “is the first estimate that exclusively focuses on the rock that is already being mined.”
Holley and her colleagues analyzed production data from permitted mining operations on U.S. federal land as well as data from more than 26,000 ore samples, each analyzed for 70 elements.
“For many of these elements, we would only have to recover 1 percent — or even less than 1 percent — of what’s currently being mined and processed and then discarded” to replace what we’re importing, Holley says. These include rare earth elements for lights, magnets and batteries; gallium for semiconductors; and tellurium for solar energy and metal alloy production.
The researchers also found that recovering less than 10 percent of the lithium, cobalt, iron and aluminum in the discarded ores could replace those imports.
Developing recovery methods would be relatively quick compared with opening new mines, Holley says. “By-product recovery, for many elements, is a low hanging fruit,” she says. “We already have what we need.”