There’s no doubt that in coming years, we’re going to need a lot of lithium. The growing market of electric automobiles, plus new household energy storage and large-scale battery farms, and the current lack of any technology better for storage than lithium ion batteries, puts the future of energy storage in the hands of just a few places around the world where the alkali metal is extracted.
Earlier this decade, researchers from the University of Michigan projected the growth in demand for lithium up until the year 2100. It’s a lot—likely somewhere between 12 million and 20 million metric tons—but those same scientists, as well as others, at the USGS and elsewhere, have estimated that global deposits well exceed those numbers. The issue is not the presence of lithium on Earth, then, but being able to get at it. Most of what we use currently comes from just a few sources, mostly in Chile and Australia, which produce 75 percent of the lithium the world uses, and also by Argentina and China, according to USGS research from 2016.
Looking to solve this problem, Stanford geologists went in search of new sources of the metal. They knew it originates in volcanic rock, and so they went to the biggest volcanoes they could find: Supervolcanoes, which appear not as a mountain with a hole in it, but a big, wide, cauldron-shaped caldera where a large-scale eruption happened millions of years ago. There, they saw high concentrations of lithium contained in a type of volcanic clay called hectorite. Geologists already knew generally that lithium came from volcanic rocks, but the team from Stanford was able to measure it in unexpected locations and quantities opening up a wider range of potential sites.
“It turns out you don’t really need super high concentrations of lithium in the magma,” says Gail Mahood, a Stanford geology professor and author of the study, in Nature Communications, about the discovery. “Many of the volcanoes that erupted in the western U.S. would have enough lithium to produce an economic deposit, as long as the eruption is big enough … and as long as [it] created a situation where you could concentrate the lithium that was leached out of the rocks.”
Currently, most of the lithium we use comes from lithium brine—salty groundwater loaded with lithium. Volcanic rocks give up their lithium as rainwater or hot hydrothermal water leaches it out of them. It runs downhill to big, geologic basins where the crust of the Earth actually stretches and sags. When that happens in particularly arid regions, the water evaporates faster than it can accumulate, and you get denser and denser concentrations of lithium. This is why the best lithium deposits so far have been in places like Clayton Valley, Nevada, and Chile’s Atacama Desert. It consolidates in a liquid brine beneath the dry desert surface, which is pumped out of the ground, condensed further in evaporation pools, and extracted from the brine in chemical plants.
LeeAnn Munk, a geologist at the University of Alaska, has been working for years to develop a “geologic recipe” of the conditions under which lithium brine forms, and her team has been the first to describe this ore deposit model—the volcanic action, the tectonic structure, the arid climate, etc. Her work, which often pairs her with the USGS, has focused on brine.
But brine is just one of the ways lithium is found. It’s well known that the metal can be found in solid rock called pegmatite, and in hectorite. Hectorite is not clay like you would use to make a pot, but a dried out, layered, white ashy substance that formed due to hydrothermal action after the volcano erupted. The clay absorbs and affixes lithium that has leached out of the volcanic rock. Because these volcanoes are old—the most notable one, perhaps, is the 16 million-year-old McDermitt Volcanic Field in Kings Valley, Nevada—the land has shifted, and the clay is often found not in a basin but exposed, up on high desert mountain ranges.
“[Mahood and her team] have identified how lithium is held in these high silica volcanic rocks,” says Munk. “It helps further our understanding of where lithium occurs, within the Earth. If we don’t fully understand that then we have a hard time telling how much lithium we have, and how much lithium we can actually extract. They’ve helped advance the understanding of where lithium exists in the crust.”
Other locations identified by Mahood’s group include Sonora, Mexico, the Yellowstone caldera, and Pantelleria, an island in the Mediterranean. Each showed varying concentrations of lithium, which the researchers were able to correlate to the concentration of the more easily-detectable elements rubidium and zirconium, meaning in the future, those can be used as indicators in the search for further lithium.
But there’s more to it than just looking for lithium-rich supervolcano sites. “The issue right now is that there’s really no existing technology at a big enough scale to actually mine the lithium out of the clays that is economical,” says Munk. “It could be something that happens in the future.”
Mahood acknowledges this. “As far as I know, people have not worked out a commercial scale process for removing lithium from hectorite,” she says. “The irony of all of this is, the hectorite is being mined right now, but it’s not actually being mined for the lithium. What they’re mining it for is the hectorite as a clay, and hectorite clays have unusual properties in that they are stable to very high temperatures. So what the deposit at King’s Valley is being mined for now is to make specialty drilling muds that are used in the natural gas and oil industry.”
But to extract lithium from brine is also expensive, particularly in the amount of fresh water it requires, in places where water is scarce. There’s probably plenty of lithium to go around, says Mahood, but you don’t want it all to come from one source. “You want it to come from diversified places in terms of both countries and companies,” she says, “so that you’re never held hostage to the pricing practices of one country.”