A research team from the University of Virginia has found a way to extract lithium from geothermal brines. The team — led by Associate Professors Geoffrey Geise and Gary Koenig, with industry partner PowerTech Water — placed second in the U.S. Department of Energy’s American-Made Geothermal Lithium Extraction Prize in which they developed a prototype of their process, called Targeted Extraction of Lithium with Electroactive Particles for Recovery Technology (TELEPORT).
The DOE commissioned the prize to speed development of direct extraction of lithium from California’s Salton Sea to establish a domestic supply of the element that can be recovered safely and economically. The U.S. currently imports about 99 percent of its supply, according to the DOE.
The TELEPORT process starts by flowing the brine — a primordial brew of mostly unwanted minerals and metals — through tubes packed with a crystalline material that acts like a lithium sponge. Atoms present in the material’s particles contain void space, said Geise.
“The electrochemistry is nearly identical to what happens in a battery. You’re moving ions into the material similarly to the movement of ions into a battery cathode during discharge,” Geise said. “The molecular space within the particles is perfectly sized for lithium ions, and other contaminant ions just don’t fit well.”
“So, we manage to quickly get rid of the ions that are problematic from the brine perspective,” Geise added. “We also greatly reduce the physical space needed for the subsequent purification process, which is economical, and the way that our special sponges work is unique compared to similar approaches because they minimize the need to add acids or other chemicals.”
That last point matters because the leftover brine will be injected back into the ground and could contaminate the wells.
The lithium is released from the sponges as lithium chloride or lithium sulfate in a solution, which is converted in TELEPORT’s next stage to bicarbonate or hydroxide, the desired form of lithium electrolyte for use in batteries.
The conversion is made in an electrolysis cell by pulling the solution across a selective membrane using electricity. This leaves the undesired molecules on one side of the cell and pairs the lithium with bicarbonate — or, in TELEPORT’s case, hydroxide on the other.
The final stage dries the lithium hydroxide that comes out of the membrane process — by now reduced in volume by many orders of magnitude from the original brine — into the powdered crystal material manufacturers need to make a battery cathode.
Here is an exclusive Tech Briefs interview — edited for length and clarity — with Geise and Koenig.
Tech Briefs: What was the biggest technical challenge you faced while developing the TELEPORT method?
Koenig: The trickiest thing is the stability of the brine itself. I think that's still always the challenge. The technology has shown a lot of promise, but it's even still really hard to know what the absolute real, at-the-source brine will do. We follow the recipe, but what actually comes out of the ground can depend on the site. But really knowing exactly what you’re using is probably one of the biggest challenges.
Geise: I’d agree with that. You like to do a lot of the early-stage development of a technology in the lab under relatively controlled circumstances where you're not making things too weird. And in so many other areas that we work in, there are standard protocols for doing that. This one kind of turned some of that up on its head, so it's an added complexity to trying to design these things.
Tech Briefs: Can you explain in simple terms how the conversion stage works?
Geise: Once we grab the lithium out of the brine, we're able to release that into a solution that we control. But when we release that, it's going to be present as some salt that contains some other anion that's not the desired hydroxide. So, we have to somehow take that lithium and marry that up with this hydroxide. And one of the ways that you can do that is to put it into this electrolysis cell. Because the lithium ion is charged, we can use electricity to selectively pull that across a membrane.
And on the side where the lithium ends up, we’re able to also use electrochemistry to generate the hydroxide ion. Essentially, we’re bringing the lithium from over here, the hydroxide’s coming in, we get the two of them to meet up, and that's ultimately how we do the conversion from what we get out of our capture process and get the lithium essentially toward the form that's desirable for the end product.
Tech Briefs: You’ve said that “the final TELEPORT stage dries the lithium hydroxide that comes out of the membrane process by now reduced in volume by many orders of magnitude from the original brine.” How much is it reduced by?
Koenig: The concentration of the lithium in the brine — basically it's the brine just before they re-inject it. So, they pull it out, they generate electricity, and then the idea is to take the stuff just before they re-inject that brine back into the ground. So, the concentration of lithium in that brine relative to the lithium in the stuff that we release from first step is about a 10-times increase in lithium concentration. Then, more importantly, most of the other stuff is gone besides maybe some sodium that still might be hanging around.
Then it’s a little bit tricky to track it as you go down through the membrane and then your final product. Your final lithium hydroxide product is going to be a solid, and the total volume of that solid relative to the volume of the same amount of lithium in the brine that originally went in is multiple orders of magnitude larger. I don't actually know if we've calculated that number.
The volume of brine being processed, which is geothermal for the electricity extraction, is huge. But the lithium concentration is relatively small, but when you multiply it by that volume of fluid, it's relatively big. And then the total amount of hydroxide product is metric tons, but it's still relatively small compared to that initial solution volume that’s going through — if that all tracks.
Geise: I guess from every liter of brine we’re probably only capturing maybe a little bit more than 200mg of lithium depending on the source, maybe 300mg.
Tech Briefs: What are your next steps?
Geise: We’re continuing to work on the technology. From the competition perspective, a lot of that was focused on initial demonstration, under a set of conditions where you could sit there and say, ‘OK, this is showing promise for working.’
As Gary alluded to in terms of one of those technical challenges, we say ‘OK, how resilient is this technology to disturbances in the feed? How much do we have to know about what's coming into the process to make it work?’ You're using a natural feedstock, so it's likely that over time things will change — you need to understand some of those operating principles.